Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects of Sustainable Forest Management

*Emilio Vilanova*

### **Abstract**

More than four decades of cumulative silvicultural experience in Venezuelan forests represents a significant progress towards sustainable forest management in the tropics. Here, based on an extensive literature review, expert opinions and discussions with forestry stakeholders in the country, we offer a broad overview of the history and current state of silvicultural practices in Venezuela's natural production forests. Despite important research advances, several factors including institutional and policy limitations, along with the lack of sound technical guidelines have hampered a more positive influence of silvicultural research for sustainable forest management across the country's managed forests. On an industrial scale, after an often poorly planned selective logging, and despite increasing evidences against for, a strong prominence of assisted natural regeneration (i.e., enrichment planting) characterized the post-logging management compared to other approaches. With very few exceptions, using artificial regeneration did not produced the expected outcomes in terms of tree growth, expected timber yield and survival. Finally, amidst the current political and economic upheaval in Venezuela, a broad range of lessons and policy recommendations is proposed including the strengthening of research on silvicultural options for multiple use of forests and for climate change mitigation and adaptation.

**Keywords:** enrichment planting, forest policy, minimum harvest diameter, research, tropical forests, Venezuela

#### **1. Introduction**

Forests in their multiple forms and types are the dominant terrestrial ecosystems on Earth, covering about one third of the globe's land area [1]. Forests represent a fundamental component of world's carbon cycle, are the habitat for biodiversity and are important for the provision of a myriad of services from which people depends for their livelihoods. Distributed over different

environmental and latitudinal gradients, forest ecosystems account for at least 75% of global terrestrial productivity (GPP) [2], with tropical forests (TFs) being disproportionally relevant compared to other forests-types in the temperate or boreal regions. For example, TFs store 200–300 Pg C, about a third as much as is held in the atmosphere [3, 4].

Globally, recent estimates indicate that the forest area under management plans, mostly for timber production, has increased since 2000 reaching close to 2.05 billion ha in 2020 [5]. However, this proportion remains largely unbalanced when compared across regions, and for example less than 20% of the total forested area of South America has some type of long-term management plan [5], while high rates of deforestation and degradation continue to threaten the stability of forests, particularly in the tropics [5–7]. In terms of forest management, more than 400 million hectares (ha) of natural tropical forests have been designated as production forests [8–10]. Moreover, nearly 40% of sawn wood traded annually in tropical regions has an origin in natural forests [11], often under a "selective logging" approach in which large trees of a relatively low number of tree species are harvested in rotation cycles of 30 years on average [9, 12, 13]. The dynamics driving how tropical forests respond, and ultimately recover to this type of intervention is a function of several ecological and socioeconomic factors. Yet, the characteristics of the logging practices (i.e. intensity of harvest, conventional vs. reduced impact logging), the elapsed time before the next harvest, and the post-harvest interventions are all silvicultural decisions particularly relevant to facilitate the speed of the recovery and the features of the future forest [14, 15]. Thus, throughout this entire process, silviculture plays an important role by ideally outlining the 'best' system and a set of specific practices to facilitate long-term forest management.

As an applied discipline, silviculture traditionally has aimed at controlling the establishment, composition, structure, growth, and the role of trees within a forest to create a more predictable production system [16, 17]. While objectives of forest management have changed globally in the last two decades with an increasing relevance for conservation of biological diversity, carbon storage, and other ecosystem services, the design, planning and application of silvicultural practices is still very much oriented towards timber production that often reduce structural and biological complexity, and has become a prevalent driver of change in many tropical managed forests [18–21]. From the outset, tropical silviculture faces the challenge of reconciling timber production as a primary goal with long-term conservation of forest ecosystems, so thresholds of extraction intensity coupled with silvicultural treatments needs to be compatible with the maintenance of biodiversity and other ecosystem services, as well as the financial viability for all the actors involved [9]. Accomplishing this goal, while difficult, seems more feasible than a few decades ago, given that the levels of ecological knowledge of tropical forests has increased enormously in the last 20 years, which means that there has never been a sounder scientific basis from which to guide forest management in the tropics [22].

This chapter discusses the history of silvicultural practices in natural forests of Venezuela, a country with one of the longest history of forest management in the tropics [23, 24] (**Figure 1**). First, an outline of the context of Venezuelan forestry is presented, including an overview of forest extension, forest types and the characteristics of forest management in the country. A review of the main silvicultural systems historically applied with considerations of their effectiveness and impacts is shown to finalize the analysis with a general proposal of recommendations to improve how forests in Venezuela could be sustainably managed in the twenty-first century.

**3**

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects…*

*DOI: http://dx.doi.org/10.5772/intechopen.93279*

**Figure 1.**

*State. Photo: Lawrence Vincent.*

**2. A general description of Venezuela's forest cover**

Venezuela has a total land area of about 916,445 km2

area covered by different types of forests [25, 26]. The variation in forest cover in Venezuela in the last three decades has followed a similar trend as in many tropical countries with a notorious peak in forest loss during the early 1990s and a slightly declining trend in deforestation rates towards the end of the twentieth century [6]. Over a longer time period, Pacheco et al. [25] found that between 1920 and 2008 Venezuela had, on average, an annual rate of forest loss of 0.30% per year, with a net decrease of 26.4% in the national forest cover for the entire period. It is around the beginning of the 1950s that a sharp increase in deforestation especially in the Western Plains ecoregion occurred, an area that remained as one of the national hotspots of deforestation for a long time [27]. With the somewhat historical unbalanced distribution of Venezuelan population, largely concentrated to the northern portion of the country, from the 36% of forest cover that was estimated to exist in this region by the mid twentieth century, some estimates place this number to as low as 10% in recent decades [24, 28], leaving the vast region of the Guiana Shield

*(a) Early forest exploration in Turén Forest Reserve, Portuguesa state, Venezuela, circa 1965. Photo: Courtesy of Giorgio Tonella; (b) forestry students in early 1970s doing forest inventory in Caparo Forest Reserve, Barinas* 

to the south of the Orinoco river as the main forested area in the country.

According to recent estimates from the Food and Agriculture Organization of the United Nations (FAO) [29] 287,500 ha, on average, were lost every year in Venezuela between 1990 and 2000 (−0.6% year−1), with a decrease in forest cover during the 2000–2010 decade of about 164,600 ha per year (−0.3% year−1). Updated statistics from public available data in Global Forest Watch (**Figure 2**) (www.globalforestwatch.org) that uses information from the study of Hansen et al. [6] indicates that from 2001 to 2018, Venezuela lost 1.95 million ha of forests (average of 108,333 ha per year), while only gained 191,000 ha of tree cover. In recent years, the spike in deforestation to the southern region in the Guiana Shield has been mostly driven by illegal gold mining [24, 28, 30]. Forests of the Western plains have been mostly cleared for agricultural purposes with current standing forests in this region being located mostly within protected areas and other inaccessible areas [24, 30], while agriculture also appeared to be a main driver of forest loss in the Andean region [31]. In Venezuela, the effects of deforestation and forest degradation in terms of carbon released have not been officially quantified. Lack of standardized methods for monitoring forest cover, the undermining of institutional capacities, and a

with 45–50% of this

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects… DOI: http://dx.doi.org/10.5772/intechopen.93279*

**Figure 1.**

*Silviculture*

much as is held in the atmosphere [3, 4].

to facilitate long-term forest management.

environmental and latitudinal gradients, forest ecosystems account for at least 75% of global terrestrial productivity (GPP) [2], with tropical forests (TFs) being disproportionally relevant compared to other forests-types in the temperate or boreal regions. For example, TFs store 200–300 Pg C, about a third as

Globally, recent estimates indicate that the forest area under management plans, mostly for timber production, has increased since 2000 reaching close to 2.05 billion ha in 2020 [5]. However, this proportion remains largely unbalanced when compared across regions, and for example less than 20% of the total forested area of South America has some type of long-term management plan [5], while high rates of deforestation and degradation continue to threaten the stability of forests, particularly in the tropics [5–7]. In terms of forest management, more than 400 million hectares (ha) of natural tropical forests have been designated as production forests [8–10]. Moreover, nearly 40% of sawn wood traded annually in tropical regions has an origin in natural forests [11], often under a "selective logging" approach in which large trees of a relatively low number of tree species are harvested in rotation cycles of 30 years on average [9, 12, 13]. The dynamics driving how tropical forests respond, and ultimately recover to this type of intervention is a function of several ecological and socioeconomic factors. Yet, the characteristics of the logging practices (i.e. intensity of harvest, conventional vs. reduced impact logging), the elapsed time before the next harvest, and the post-harvest interventions are all silvicultural decisions particularly relevant to facilitate the speed of the recovery and the features of the future forest [14, 15]. Thus, throughout this entire process, silviculture plays an important role by ideally outlining the 'best' system and a set of specific practices

As an applied discipline, silviculture traditionally has aimed at controlling the establishment, composition, structure, growth, and the role of trees within a forest to create a more predictable production system [16, 17]. While objectives of forest management have changed globally in the last two decades with an increasing relevance for conservation of biological diversity, carbon storage, and other ecosystem services, the design, planning and application of silvicultural practices is still very much oriented towards timber production that often reduce structural and biological complexity, and has become a prevalent driver of change in many tropical managed forests [18–21]. From the outset, tropical silviculture faces the challenge of reconciling timber production as a primary goal with long-term conservation of forest ecosystems, so thresholds of extraction intensity coupled with silvicultural treatments needs to be compatible with the maintenance of biodiversity and other ecosystem services, as well as the financial viability for all the actors involved [9]. Accomplishing this goal, while difficult, seems more feasible than a few decades ago, given that the levels of ecological knowledge of tropical forests has increased enormously in the last 20 years, which means that there has never been a sounder scientific basis from which to guide forest management in the

This chapter discusses the history of silvicultural practices in natural forests of Venezuela, a country with one of the longest history of forest management in the tropics [23, 24] (**Figure 1**). First, an outline of the context of Venezuelan forestry is presented, including an overview of forest extension, forest types and the characteristics of forest management in the country. A review of the main silvicultural systems historically applied with considerations of their effectiveness and impacts is shown to finalize the analysis with a general proposal of recommendations to improve how forests in Venezuela could be sustainably managed in the twenty-first

**2**

century.

tropics [22].

*(a) Early forest exploration in Turén Forest Reserve, Portuguesa state, Venezuela, circa 1965. Photo: Courtesy of Giorgio Tonella; (b) forestry students in early 1970s doing forest inventory in Caparo Forest Reserve, Barinas State. Photo: Lawrence Vincent.*

#### **2. A general description of Venezuela's forest cover**

Venezuela has a total land area of about 916,445 km2 with 45–50% of this area covered by different types of forests [25, 26]. The variation in forest cover in Venezuela in the last three decades has followed a similar trend as in many tropical countries with a notorious peak in forest loss during the early 1990s and a slightly declining trend in deforestation rates towards the end of the twentieth century [6]. Over a longer time period, Pacheco et al. [25] found that between 1920 and 2008 Venezuela had, on average, an annual rate of forest loss of 0.30% per year, with a net decrease of 26.4% in the national forest cover for the entire period. It is around the beginning of the 1950s that a sharp increase in deforestation especially in the Western Plains ecoregion occurred, an area that remained as one of the national hotspots of deforestation for a long time [27]. With the somewhat historical unbalanced distribution of Venezuelan population, largely concentrated to the northern portion of the country, from the 36% of forest cover that was estimated to exist in this region by the mid twentieth century, some estimates place this number to as low as 10% in recent decades [24, 28], leaving the vast region of the Guiana Shield to the south of the Orinoco river as the main forested area in the country.

According to recent estimates from the Food and Agriculture Organization of the United Nations (FAO) [29] 287,500 ha, on average, were lost every year in Venezuela between 1990 and 2000 (−0.6% year−1), with a decrease in forest cover during the 2000–2010 decade of about 164,600 ha per year (−0.3% year−1). Updated statistics from public available data in Global Forest Watch (**Figure 2**) (www.globalforestwatch.org) that uses information from the study of Hansen et al. [6] indicates that from 2001 to 2018, Venezuela lost 1.95 million ha of forests (average of 108,333 ha per year), while only gained 191,000 ha of tree cover. In recent years, the spike in deforestation to the southern region in the Guiana Shield has been mostly driven by illegal gold mining [24, 28, 30]. Forests of the Western plains have been mostly cleared for agricultural purposes with current standing forests in this region being located mostly within protected areas and other inaccessible areas [24, 30], while agriculture also appeared to be a main driver of forest loss in the Andean region [31].

In Venezuela, the effects of deforestation and forest degradation in terms of carbon released have not been officially quantified. Lack of standardized methods for monitoring forest cover, the undermining of institutional capacities, and a

#### **Figure 2.**

*Total annual forest cover loss (in thousands of hectares per year) in Venezuela for the 2001–2018 period using different proportions of forest canopy cover. Each category includes a linear trend. The figure was built using public data available from the global forest watch (www.globalforestwatch.org).*

dramatic decline in professional training, among other factors, helps explaining this situation. However, reviewing the literature in this topic we find few studies that have shown that carbon emissions due to deforestation and forest degradation in Venezuela can be significant. Most of these studies have been conducted at global or pantropical scales and includes a reference for Venezuela. For example, Harris et al. [32] estimated that, between 2000 and 2005, about 9 Tg C year−1 (units are 1012 grams of carbon per year) were lost due to deforestation in Venezuela. This estimation might have represented between 9 and 28% of national emissions during the last decade [30]. Additionally, Pearson et al. [33] found for the 2005–2010 period that close to 10% of Venezuelan carbon emissions came from forest degradation, including selective logging, wood fuel harvest, fires and grazing as the main factors.

#### **3. Environmental setting and forest-types in Venezuela**

Located in the northern portion of South America, slightly above the equator, like much of the tropical region, Venezuela is largely subjected to the influence of the intertropical convergence zone (ITCZ), which affects rainfall patterns and results in the existence of wet and dry seasons in comparison to the cold and warm seasons of higher latitudes. ITCZ's position, structure, and migration influence the oceanatmosphere and land-atmosphere interactions on a local scale, the circulation of the tropical oceans on a basin scale, and a number of features of the Earth's climate on a global scale [34]. Land form and relief, or the physiographical features in the land in Venezuela, largely expressed by the existence of three major mountain systems and different types of plains and savannas are a major driver of the seasonal and geographical patterns in rainfall in Venezuela at local and regional scales [35]. At least two major gradients in the distribution of precipitation in the country have been described: one from the Northeastern Atlantic to the Andes in the west, and a second one from the Caribbean Sea to the southern Amazonian flatlands. Annual precipitation in Venezuela ranges from less than 400 mm per year in some of the

**5**

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects…*

driest portions of the country up to about 4500 mm year−1, which along with its seasonal distribution influence the type and characteristics of the vegetation [35]. From the standpoint of temperature, though much less variable than precipitation, there are important differences at regional scales, mostly as a response of elevation and latitude. With an elevation range from sea level up to close to 5000 m in the peaks of the Andean mountains, temperature varies accordingly [36]. Consequently, a highly diverse vegetation can be found across the country, where up to 18 different types have been identified with lowland evergreen forests largely dominating the nation's landscapes [35]. Other important formations include the cloud forests restricted to a rather narrow elevation gradient in different mountainous areas of the country, palm-dominated and swamp forests in the Orinoco Delta, mangroves, riparian and semi-deciduous forests across much of the savanna and the plains, and different expressions of shrub-like vegetation, grasslands and savannas. In fact, savannas might account for close to 25% of the country's land area with major continuous savannas located in the central Orinoco Plains (*Llanos*) limited by the Andean and Coastal Mountains to the west and north, respectively, and with a second large savanna in the Guiana Plateau (*Gran Sabana*) in the southeast of the country [37].

Venezuela is a tropical country having made one of the longest and continuous effort towards natural forest management (NFM), especially under long-term concession tracts in Tropical America. During the 1970s, the introduction of a forest concession system represented a significant advancement towards NFM at a regional level [24, 38, 39]. The first private concessions were allocated in 1970 and were probably the first known attempt to formally develop long-term management plans in the tropics, including silvicultural practices as a core component. By 1992, almost 3.2 million ha were allocated in more than 30 forest management units (FMUs) and had management plans approved by the national government [40]. In 1995, the national government planned a significant increase in the area under forestry concessions to 10 million ha over 5 years but the country's adoption of new policies and the rising criticism to forest management strategies prevented this from happening [24]. This process led to a significant decline in timber production coming from FMUs. For instance, in 1987 almost 40% of the national round wood production came from natural managed forests [40], while this proportion dropped to only 7% 20 years later [41], shifting the demand for timber products essentially to plantations. Albeit the lack of good quality indicators that has characterized the last decade in terms of forest statistics nationwide, the last available official data from 2018 indicates that only 2.5% of the wood legally consumed in the country came from FMUs in an estimated area of 246,313 ha of forests with formal management plans [42] (**Table 1**). Several analyses of the forest management model applied in Venezuela have highlighted critical limitations in multiple aspects of the management process, including planning deficiencies, inadequate policies, and overall an insufficient application of sustainable management guidelines during forest operations. While some of the reasons behind this situation may fall outside the specific realms of forest management activities, there is consensus that forest management practices have not contributed to guarantee the long-term permanence of production forests nationwide [40, 43–45]. In a 2011 pantropical assessment led by the International Tropical Timber Organization (ITTO) [8], after almost four decades of NFM in

*DOI: http://dx.doi.org/10.5772/intechopen.93279*

**4. Management of natural forests in Venezuela**

**4.1 General overview**

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects… DOI: http://dx.doi.org/10.5772/intechopen.93279*

driest portions of the country up to about 4500 mm year−1, which along with its seasonal distribution influence the type and characteristics of the vegetation [35].

From the standpoint of temperature, though much less variable than precipitation, there are important differences at regional scales, mostly as a response of elevation and latitude. With an elevation range from sea level up to close to 5000 m in the peaks of the Andean mountains, temperature varies accordingly [36]. Consequently, a highly diverse vegetation can be found across the country, where up to 18 different types have been identified with lowland evergreen forests largely dominating the nation's landscapes [35]. Other important formations include the cloud forests restricted to a rather narrow elevation gradient in different mountainous areas of the country, palm-dominated and swamp forests in the Orinoco Delta, mangroves, riparian and semi-deciduous forests across much of the savanna and the plains, and different expressions of shrub-like vegetation, grasslands and savannas. In fact, savannas might account for close to 25% of the country's land area with major continuous savannas located in the central Orinoco Plains (*Llanos*) limited by the Andean and Coastal Mountains to the west and north, respectively, and with a second large savanna in the Guiana Plateau (*Gran Sabana*) in the southeast of the country [37].

#### **4. Management of natural forests in Venezuela**

#### **4.1 General overview**

*Silviculture*

**Figure 2.**

dramatic decline in professional training, among other factors, helps explaining this situation. However, reviewing the literature in this topic we find few studies that have shown that carbon emissions due to deforestation and forest degradation in Venezuela can be significant. Most of these studies have been conducted at global or pantropical scales and includes a reference for Venezuela. For example, Harris et al. [32] estimated that, between 2000 and 2005, about 9 Tg C year−1 (units are 1012 grams of carbon per year) were lost due to deforestation in Venezuela. This estimation might have represented between 9 and 28% of national emissions during the last decade [30]. Additionally, Pearson et al. [33] found for the 2005–2010 period that close to 10% of Venezuelan carbon emissions came from forest degradation, including selective logging, wood fuel harvest, fires and grazing as the main factors.

*Total annual forest cover loss (in thousands of hectares per year) in Venezuela for the 2001–2018 period using different proportions of forest canopy cover. Each category includes a linear trend. The figure was built using* 

Located in the northern portion of South America, slightly above the equator, like much of the tropical region, Venezuela is largely subjected to the influence of the intertropical convergence zone (ITCZ), which affects rainfall patterns and results in the existence of wet and dry seasons in comparison to the cold and warm seasons of higher latitudes. ITCZ's position, structure, and migration influence the oceanatmosphere and land-atmosphere interactions on a local scale, the circulation of the tropical oceans on a basin scale, and a number of features of the Earth's climate on a global scale [34]. Land form and relief, or the physiographical features in the land in Venezuela, largely expressed by the existence of three major mountain systems and different types of plains and savannas are a major driver of the seasonal and geographical patterns in rainfall in Venezuela at local and regional scales [35]. At least two major gradients in the distribution of precipitation in the country have been described: one from the Northeastern Atlantic to the Andes in the west, and a second one from the Caribbean Sea to the southern Amazonian flatlands. Annual precipitation in Venezuela ranges from less than 400 mm per year in some of the

**3. Environmental setting and forest-types in Venezuela**

*public data available from the global forest watch (www.globalforestwatch.org).*

**4**

Venezuela is a tropical country having made one of the longest and continuous effort towards natural forest management (NFM), especially under long-term concession tracts in Tropical America. During the 1970s, the introduction of a forest concession system represented a significant advancement towards NFM at a regional level [24, 38, 39]. The first private concessions were allocated in 1970 and were probably the first known attempt to formally develop long-term management plans in the tropics, including silvicultural practices as a core component. By 1992, almost 3.2 million ha were allocated in more than 30 forest management units (FMUs) and had management plans approved by the national government [40]. In 1995, the national government planned a significant increase in the area under forestry concessions to 10 million ha over 5 years but the country's adoption of new policies and the rising criticism to forest management strategies prevented this from happening [24]. This process led to a significant decline in timber production coming from FMUs. For instance, in 1987 almost 40% of the national round wood production came from natural managed forests [40], while this proportion dropped to only 7% 20 years later [41], shifting the demand for timber products essentially to plantations. Albeit the lack of good quality indicators that has characterized the last decade in terms of forest statistics nationwide, the last available official data from 2018 indicates that only 2.5% of the wood legally consumed in the country came from FMUs in an estimated area of 246,313 ha of forests with formal management plans [42] (**Table 1**).

Several analyses of the forest management model applied in Venezuela have highlighted critical limitations in multiple aspects of the management process, including planning deficiencies, inadequate policies, and overall an insufficient application of sustainable management guidelines during forest operations. While some of the reasons behind this situation may fall outside the specific realms of forest management activities, there is consensus that forest management practices have not contributed to guarantee the long-term permanence of production forests nationwide [40, 43–45]. In a 2011 pantropical assessment led by the International Tropical Timber Organization (ITTO) [8], after almost four decades of NFM in


*a Modified from the last available official forest statistic report from 2018 [42]. Production forests are classified as category VI as per the International Union of Conservation of Nature (IUCN) guidelines to label protected areas with sustainable use of natural resources.*

*b Venezuela has a complex system of natural protected areas (NPAs). These are managed for specific purposes according to special laws and were designated as "*áreas de administración especial*" – ABRAE (Areas under Special Administration), which includes up to 25 different categories including National Parks, Natural monuments, wildlife refuge, among others. More info on Venezuela's protected areas can be found elsewhere (e.g. [24, 28]). c Includes overlapping in some protected areas which implies the net area protected is lower.*

*d Relative proportion is given based on the total forest production area of 11,183,202 ha.*

*e Planted forests are not part of the ABRAE system. This area is based on 2014 data from the official government report [46] submitted to the 2015 Global Forest Resource Assessment program from FAO (http://www.fao.org/ forest-resources-assessment/en/). Includes timber production from forest plantations mainly of exotics species such as Caribbean Pine (*Pinus caribaea*), Eucalyptus (*Eucalyptus sp*.) and Teak (*Tectona grandis*).*

#### **Table 1.**

*General overview of the forest sector in Venezuela.*

Venezuela, of the approximately 12 million ha of production forests, a very low proportion of close to 0.03% was considered as being sustainably managed. Moreover, Venezuela is one of the few tropical countries with no certified forest management operations in natural forests. In addition, although a modest progress has been made to establish a more inclusive approach to include local communities in the application and benefits of forest management, the few community-based cases that did exist have resulted in deforestation and degradation of forests [44, 47]. Also, there is no detailed information on the distribution of formal and informal employment in the Venezuelan forestry sector to quantify the social impact generated by this activity. Available data indicates that forestry's contribution to national gross domestic product (GDP) was between 0.5 and 1% in 2005 according to Carrero and Andrade [48], but historical economic trends suggest that this proportion is likely to have considerably reduced in recent years.

In recent years, with the enactment of the new *Forests and Forest Management Law* in 2008, later revised in 2013, a policy shift began with regards to how forest management should be planned and applied in Venezuela. Perhaps, the most novel aspect of this process was the creation in 2010 of a public government-based forest company (*Empresa Nacional Forestal* – National Forest Company). Broadly, the general objective is to promote the *"…sustainable production of forest goods and services, through the planning and management of the forest heritage (…) aimed at promoting the direct participation of local communities and other organizations*…" [49]. In practice,

**7**

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects…*

along with government agencies, this company currently oversees the guidelines for developing new forest management plans while slowly substituted the model of private concessions previously in place. At present, the company supervises the management for all production forests in the country and has an active management operation in the Imataca Forest Reserve in Eastern Venezuela. In addition, with the support of FAO, a 5-year project started in 2016 aiming at connecting multiple components (e.g. Reduced Impact Logging, ecological restoration, silviculture, research) to support the development of sustainable forest management guidelines

The impacts of this initiative are yet to be assessed.

**4.2 Historical perspective of silvicultural practices in Venezuela's production** 

With the beginning of major development projects in the second half of the twentieth century, it became clear that a significant area of forests in the country represented, on one hand, environments of high ecological value that had to be preserved and that is how the main foundations of the national system of protected areas (ABRAE) were laid. On the other, some of these areas also showed characteristics that made them important resources for the development of local and regional economies across the country and a significant component for a forest-based

As in many tropical countries, the beginnings of forestry in Venezuela were influenced by practices extrapolated mostly from experiences applied in European temperate forests [20, 50, 51], especially on topics related to methods to promote the regeneration of the harvested forest. In its early days, the forestry practice in Venezuela was grounded on the conceptual premise of the so-called "experimental management" through two variations upon different intensities in the prescription of silvicultural treatments [52]. This concept of experimental management was based on the need to manage production forests, even under conditions of lack of enough sound scientific information being available. Thus, conducting forest management as an "experiment" implied the existence of a set of guidelines in which there is a research program in place to test various silvicultural alternatives while

In practice, this approach was later defined as a combination between active and passive management approaches [24, 54], and was influential during the early days of forest policy and management in the Forest Reserves of the Western Plains region (i.e. Ticoporo, Caparo, San Camilo – **Figure 3**). From the theoretical stand point, passive management meant that forests were managed via seemingly very low intensity treatments, on the assumption of natural and spontaneous production without silvicultural treatments, while timber harvest was properly regulated in intensity and environmental impacts [52, 54]. Generally speaking, this approach and its guidelines fit well with sustainable forest management practices that have been promoted based on reduced impact logging (RIL) in many tropical regions [45, 55–57]. However, as has been widely documented (e.g. [23, 24, 43, 44, 58]), its implementation was poorly executed often with negative environmental effects [45, 59, 60]. Secondly, the active management approach was characterized for concentrating intensive practices over relatively small areas. The main objective was the "improvement" of the forest composition mostly through directing the intervention towards species with high commercial value and with low natural abundance or that were completely absent in the forest stand. These practices ranged from relatively low-intensity practices (e.g. assisted natural

management is simultaneously applied on a commercial scale [53].

<sup>1</sup> http://www.fao.org/venezuela/programas-y-proyectos/lista-de-proyectos/es/

<sup>2</sup> http://sigot.geoportalsb.gob.ve/abrae\_web/index.php

*DOI: http://dx.doi.org/10.5772/intechopen.93279*

at national scale.1

**forests**

productive sector (**Figure 3**).2

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects… DOI: http://dx.doi.org/10.5772/intechopen.93279*

along with government agencies, this company currently oversees the guidelines for developing new forest management plans while slowly substituted the model of private concessions previously in place. At present, the company supervises the management for all production forests in the country and has an active management operation in the Imataca Forest Reserve in Eastern Venezuela. In addition, with the support of FAO, a 5-year project started in 2016 aiming at connecting multiple components (e.g. Reduced Impact Logging, ecological restoration, silviculture, research) to support the development of sustainable forest management guidelines at national scale.1 The impacts of this initiative are yet to be assessed.

#### **4.2 Historical perspective of silvicultural practices in Venezuela's production forests**

With the beginning of major development projects in the second half of the twentieth century, it became clear that a significant area of forests in the country represented, on one hand, environments of high ecological value that had to be preserved and that is how the main foundations of the national system of protected areas (ABRAE) were laid. On the other, some of these areas also showed characteristics that made them important resources for the development of local and regional economies across the country and a significant component for a forest-based productive sector (**Figure 3**).2

As in many tropical countries, the beginnings of forestry in Venezuela were influenced by practices extrapolated mostly from experiences applied in European temperate forests [20, 50, 51], especially on topics related to methods to promote the regeneration of the harvested forest. In its early days, the forestry practice in Venezuela was grounded on the conceptual premise of the so-called "experimental management" through two variations upon different intensities in the prescription of silvicultural treatments [52]. This concept of experimental management was based on the need to manage production forests, even under conditions of lack of enough sound scientific information being available. Thus, conducting forest management as an "experiment" implied the existence of a set of guidelines in which there is a research program in place to test various silvicultural alternatives while management is simultaneously applied on a commercial scale [53].

In practice, this approach was later defined as a combination between active and passive management approaches [24, 54], and was influential during the early days of forest policy and management in the Forest Reserves of the Western Plains region (i.e. Ticoporo, Caparo, San Camilo – **Figure 3**). From the theoretical stand point, passive management meant that forests were managed via seemingly very low intensity treatments, on the assumption of natural and spontaneous production without silvicultural treatments, while timber harvest was properly regulated in intensity and environmental impacts [52, 54]. Generally speaking, this approach and its guidelines fit well with sustainable forest management practices that have been promoted based on reduced impact logging (RIL) in many tropical regions [45, 55–57]. However, as has been widely documented (e.g. [23, 24, 43, 44, 58]), its implementation was poorly executed often with negative environmental effects [45, 59, 60]. Secondly, the active management approach was characterized for concentrating intensive practices over relatively small areas. The main objective was the "improvement" of the forest composition mostly through directing the intervention towards species with high commercial value and with low natural abundance or that were completely absent in the forest stand. These practices ranged from relatively low-intensity practices (e.g. assisted natural

*Silviculture*

**Descriptiona Total area** 

Wood production Volume (m3

National roundwood production in 2017 (m3

)

)

*General overview of the forest sector in Venezuela.*

*with sustainable use of natural resources.*

Reserves in 2017 (m3

Reserves in 2017 (m3

*a*

*b*

*c*

*d*

*e*

**Table 1.**

National roundwood production outside Forest

National roundwood production inside Forest

Areas under special administration (n = 382)b 67,883,078c — Natural forest production areas 11,183,202 16.5% Forest reserves (n = 10) 6,742,047 9.9% Forest lots (n = 4) 967,093 1.4% Forest areas under protection (n = 43) 3,473,702 5.2% Area with approved forest management plans 246,313 2.2%d Area of forest plantations for wood productione 557,324 —

)

*Modified from the last available official forest statistic report from 2018 [42]. Production forests are classified as category VI as per the International Union of Conservation of Nature (IUCN) guidelines to label protected areas* 

*Venezuela has a complex system of natural protected areas (NPAs). These are managed for specific purposes according to special laws and were designated as "*áreas de administración especial*" – ABRAE (Areas under Special Administration), which includes up to 25 different categories including National Parks, Natural monuments, wildlife refuge, among others. More info on Venezuela's protected areas can be found elsewhere (e.g. [24, 28]).*

*Planted forests are not part of the ABRAE system. This area is based on 2014 data from the official government report [46] submitted to the 2015 Global Forest Resource Assessment program from FAO (http://www.fao.org/ forest-resources-assessment/en/). Includes timber production from forest plantations mainly of exotics species such as* 

*Includes overlapping in some protected areas which implies the net area protected is lower.*

*Caribbean Pine (*Pinus caribaea*), Eucalyptus (*Eucalyptus sp*.) and Teak (*Tectona grandis*).*

*Relative proportion is given based on the total forest production area of 11,183,202 ha.*

**(ha)**

<sup>e</sup> 496,748 —

484,429 97.5%

12,319 2.5%

**Relative proportion of the total area (%)**

) Relative proportion of total volume (%)

**6**

Venezuela, of the approximately 12 million ha of production forests, a very low proportion of close to 0.03% was considered as being sustainably managed. Moreover, Venezuela is one of the few tropical countries with no certified forest management operations in natural forests. In addition, although a modest progress has been made to establish a more inclusive approach to include local communities in the application and benefits of forest management, the few community-based cases that did exist have resulted in deforestation and degradation of forests [44, 47]. Also, there is no detailed information on the distribution of formal and informal employment in the Venezuelan forestry sector to quantify the social impact generated by this activity. Available data indicates that forestry's contribution to national gross domestic product (GDP) was between 0.5 and 1% in 2005 according to Carrero and Andrade [48], but historical economic trends suggest that this

In recent years, with the enactment of the new *Forests and Forest Management Law* in 2008, later revised in 2013, a policy shift began with regards to how forest management should be planned and applied in Venezuela. Perhaps, the most novel aspect of this process was the creation in 2010 of a public government-based forest company (*Empresa Nacional Forestal* – National Forest Company). Broadly, the general objective is to promote the *"…sustainable production of forest goods and services, through the planning and management of the forest heritage (…) aimed at promoting the direct participation of local communities and other organizations*…" [49]. In practice,

proportion is likely to have considerably reduced in recent years.

<sup>1</sup> http://www.fao.org/venezuela/programas-y-proyectos/lista-de-proyectos/es/

<sup>2</sup> http://sigot.geoportalsb.gob.ve/abrae\_web/index.php

#### **Figure 3.**

*General distribution of natural production forests in Venezuela. There are legal differences in terms of how forest reserves and lots are administered, but along with the group of 39 Forest areas under protection these are all public-managed areas. In 2018,* El Caura *Forest Reserve in the Guiana Shield region, with more than 5 million ha officially became the 44th National Park. Therefore, the total area shown in Table 2 excludes this reserve. Map elaborated by Carlos Pacheco based on publicly available data of Venezuela's protected areas.*

regeneration) to more intensive options including a total forest conversion of the selectively logged forest to fast-growing plantations mostly with exotic species [23, 52, 54].

Although no specific rules were set to determine how each approach should be spatially applied, Vincent [61] proposed that the selection and designation of the active management areas should be carried out in each annual compartment or, preferably, by sets of compartments only in the "best" sites (i.e. high productivity, mostly flat with relatively good drained soils). For instance, in the units of the Western Plains where this approach was implemented, active management was executed in close to 10% of the total managed area. The rest of the annual compartment, typically in areas on average of about 2000 ha in 25–30 years cutting cycles, was managed under the passive approach using selective logging upon a group of previously set minimum harvesting diameters (MHDs) for commercial timber species, and the marking and mapping of future commercial trees including those designated for seed production.

As has been documented in different analysis focusing on the tropics (e.g. [21, 22]), silvicultural practices applied in the management of Venezuela's production forests had the fundamental objective of solving the "problem" of a relatively low regeneration of many commercial species and, when possible, to secure sustained volumes of timber within cutting cycles typically of 25–30 years, although 40-year cycles were common in management plans for less productive forests of the Guiana Shield. Many of these practices have been strongly criticized [23, 24, 44, 62], because they frequently ignored the importance of pre-harvest planning operations and the complex ecology and dynamics of tropical forests. Thus, these practices generally neither increased the productivity of the system nor contributed to its sustainability [24].

**9**

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects…*

Forest Reserve in the Western Plains region, a great deal of effort was put into the understanding of the basic ecology of many forest species with timber value. Looking for effective and efficient systems, not only basic information on the ecology of the species was collected (i.e. phenology, reproduction, dispersal strategies, growth), but also a large number of these potential species was part of multiple experiments in which different planting and management conditions were tested, including open-field trials and enrichment planting in strips with different variations [63]. This is probably one of the most successful aspects of the Research Program, that is producing a baseline of applicable information on the ecology and management of several species in the Western Plains. The use of teak (*Tectona grandis*), an exotic species deserves a special mention as this species optimally acclimatized and resulted in highly productive stands specially in well-drained sites [24]. Teak plantations were often established in open field conditions in deforested areas, but several logging companies used teak after full conversion of logged forests as part of their "active" management plans [23]. Since 1970, and fundamentally since the creation of the Graduate Center for Forest and Environmental Studies (CEFAP) in 1968, a large cumulative experience in tropical silviculture exist, but with a limited application at the operational and commercial scales. Much of this experience is sustained on a research program that included multiple silvicultural trials and experiments that, for reasons analyzed later in this chapter, were not fully applied on a larger scale. As documented by Putz and Ruslandi [56] for the tropical region, between plantation conversion and single-tree selection using RIL, there is a wide variety of silvicultural interventions that tropical foresters can apply but these are rarely used outside of experimental plots. Silvicultural methods such as shelterwoods, group selection and others all have received considerable attention from research, but with a few exceptions, most have not been formally adopted at industrial or commercial scales. In the next

sections, some of the most prominent silvicultural practices are described.

An extensive literature review was conducted to compile and characterize the most common silvicultural systems used in Venezuela's production forests (**Table 2**). This process included peer-reviewed studies, but most of all was based on the analysis of numerous official reports from the national forest agencies, a review of different management plans from private companies and the results from surveys distributed widely among different stakeholders linked to forest management in Venezuela. The reader will find that the topic of plantation forestry has been purposely ignored (but see [24] for more information), while others such as the use of non-timber forest products (NTFP) and its management lacked of sufficient information to offer a comprehensive analysis. Nevertheless, the following section is by far the most updated review of the history and characteristics of silvicultural practices applied in natural

Probably the oldest and most widespread management system applied in the tropics. After a pre-harvest inventory, a minimum harvest diameter is established to determine mature commercial trees and is the basis of the polycyclic management, a selection approach where, in theory, the objective is to control overexploitation of the forests by harvesting a relatively low number of commercial trees [64]. It is essentially a system based on natural forest production where the only direct intervention is selective harvesting repeated within moderately short cutting cycles [65]. It is a highly selective

**4.3 Common silvicultural systems and practices**

production forests in Venezuela.

*4.3.1 Minimum harvest diameters (MHDs)*

Within the Forest Management Research Program that began in 1970 in the Caparo

*DOI: http://dx.doi.org/10.5772/intechopen.93279*

#### *Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects… DOI: http://dx.doi.org/10.5772/intechopen.93279*

Within the Forest Management Research Program that began in 1970 in the Caparo Forest Reserve in the Western Plains region, a great deal of effort was put into the understanding of the basic ecology of many forest species with timber value. Looking for effective and efficient systems, not only basic information on the ecology of the species was collected (i.e. phenology, reproduction, dispersal strategies, growth), but also a large number of these potential species was part of multiple experiments in which different planting and management conditions were tested, including open-field trials and enrichment planting in strips with different variations [63]. This is probably one of the most successful aspects of the Research Program, that is producing a baseline of applicable information on the ecology and management of several species in the Western Plains. The use of teak (*Tectona grandis*), an exotic species deserves a special mention as this species optimally acclimatized and resulted in highly productive stands specially in well-drained sites [24]. Teak plantations were often established in open field conditions in deforested areas, but several logging companies used teak after full conversion of logged forests as part of their "active" management plans [23].

Since 1970, and fundamentally since the creation of the Graduate Center for Forest and Environmental Studies (CEFAP) in 1968, a large cumulative experience in tropical silviculture exist, but with a limited application at the operational and commercial scales. Much of this experience is sustained on a research program that included multiple silvicultural trials and experiments that, for reasons analyzed later in this chapter, were not fully applied on a larger scale. As documented by Putz and Ruslandi [56] for the tropical region, between plantation conversion and single-tree selection using RIL, there is a wide variety of silvicultural interventions that tropical foresters can apply but these are rarely used outside of experimental plots. Silvicultural methods such as shelterwoods, group selection and others all have received considerable attention from research, but with a few exceptions, most have not been formally adopted at industrial or commercial scales. In the next sections, some of the most prominent silvicultural practices are described.

#### **4.3 Common silvicultural systems and practices**

An extensive literature review was conducted to compile and characterize the most common silvicultural systems used in Venezuela's production forests (**Table 2**). This process included peer-reviewed studies, but most of all was based on the analysis of numerous official reports from the national forest agencies, a review of different management plans from private companies and the results from surveys distributed widely among different stakeholders linked to forest management in Venezuela. The reader will find that the topic of plantation forestry has been purposely ignored (but see [24] for more information), while others such as the use of non-timber forest products (NTFP) and its management lacked of sufficient information to offer a comprehensive analysis. Nevertheless, the following section is by far the most updated review of the history and characteristics of silvicultural practices applied in natural production forests in Venezuela.

#### *4.3.1 Minimum harvest diameters (MHDs)*

Probably the oldest and most widespread management system applied in the tropics. After a pre-harvest inventory, a minimum harvest diameter is established to determine mature commercial trees and is the basis of the polycyclic management, a selection approach where, in theory, the objective is to control overexploitation of the forests by harvesting a relatively low number of commercial trees [64]. It is essentially a system based on natural forest production where the only direct intervention is selective harvesting repeated within moderately short cutting cycles [65]. It is a highly selective

*Silviculture*

**Figure 3.**

**8**

regeneration) to more intensive options including a total forest conversion of the selectively logged forest to fast-growing plantations mostly with exotic species [23, 52, 54]. Although no specific rules were set to determine how each approach should be spatially applied, Vincent [61] proposed that the selection and designation of the active management areas should be carried out in each annual compartment or, preferably, by sets of compartments only in the "best" sites (i.e. high productivity, mostly flat with relatively good drained soils). For instance, in the units of the Western Plains where this approach was implemented, active management was executed in close to 10% of the total managed area. The rest of the annual compartment, typically in areas on average of about 2000 ha in 25–30 years cutting cycles, was managed under the passive approach using selective logging upon a group of previously set minimum harvesting diameters (MHDs) for commercial timber species, and the marking and mapping of future commercial trees including those designated for seed production. As has been documented in different analysis focusing on the tropics (e.g. [21, 22]), silvicultural practices applied in the management of Venezuela's production forests had the fundamental objective of solving the "problem" of a relatively low regeneration of many commercial species and, when possible, to secure sustained volumes of timber within cutting cycles typically of 25–30 years, although 40-year cycles were common in management plans for less productive forests of the Guiana Shield. Many of these practices have been strongly criticized [23, 24, 44, 62], because they frequently ignored the importance of pre-harvest planning operations and the complex ecology and dynamics of tropical forests. Thus, these practices generally neither increased the

*General distribution of natural production forests in Venezuela. There are legal differences in terms of how forest reserves and lots are administered, but along with the group of 39 Forest areas under protection these are all public-managed areas. In 2018,* El Caura *Forest Reserve in the Guiana Shield region, with more than 5 million ha officially became the 44th National Park. Therefore, the total area shown in Table 2 excludes this reserve. Map elaborated by Carlos Pacheco based on publicly available data of Venezuela's protected areas.*

productivity of the system nor contributed to its sustainability [24].


**11**

*4.3.2 Post-logging silvicultural treatments*

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects…*

• Its application is justified on the basis of the maintenance of enough crop trees to ensure a sustainable harvest under polycyclic schemes; • Typically accompanied by intermediate treatments to reduce competition on crop tress.

**Silvicultural systema Reasons for its implementation Region or area of the country** 

**where it is applied or may be applicable and main species** 

• Widely applied in the forest management of the Western Plains and today in the Guiana

• If logging is the unique treatment, it is often not considered a formal silvicultural system.

**used**

Shield.

management system in terms of the spectrum of commercial species and the relatively low number of trees logged that is common in many tropical managed forests (1–20 trees per ha -[67]). Under these conditions, it was expected that with a proper planning with minimum standards for cutting and transportation activities, the impacts on the forest stand would be low and facilitate a consistent flow of timber in the next cutting cycles [20, 51, 64]. This system was the fundamental basis of the first forest harvesting permits granted in Venezuela more than 40 years ago [23], and remained relatively unaltered even at times when research evidences made clear that major modifications to this approach were urgent in support of long-term sustainable management [44, 68–70]. Most frequently, these MHDs are set by national authorities, and depending on the species groups and their commercial value, values are typically within the range of 30 up to 70 cm or more in diameter at breast height (DBH) [64]. However, these limits are mostly set to accommodate processing technologies and market demands, rather than the biology and persistence of the harvested species, limiting the possibility to provide ecologically sustainable forest management [71]. Remarkably high numbers of species that are common in many tropical differ in growth requirements, growth rates, marketability, ecological roles and other relevant traits. Thus, simple silvicultural guidelines such as fixed MHDs or cutting cycles are unlikely to be satisfactory [13]. In Venezuela's case, the lack of sound ecological information on growth patterns of commercial species, density and structure, along with limited long-term information has been highlighted as a major limitation [23, 24, 69, 72]. A relatively new official regulation related to MHDs enacted in 2009 [73] aimed at solving, at least partly, the lack of data on species growth by expanding the information on the number of species with MHDs. However, if no improvement is made to the overall process of forest planning, including the urgent implementation of reduced impact logging, and a rethinking of cutting cycles the negative perception towards timber harvest is likely to persist (**Figure 4**).

*Silvicultural systems applied or potentially applicable in Venezuela's production forests.*

*This grouping of silvicultural systems is presented based on practical experiences, results of applied research or based on the analysis of the ecological conditions of forests that would make a particular system applicable. In all cases,* 

In many tropical managed forests, a group of standard practices are often applied after selective logging to reduce competition for future harvestable trees. These intermediate treatments might include *refining*, that is, the elimination of undesirable tree species or sick or damaged material, to the extent only that the

*DOI: http://dx.doi.org/10.5772/intechopen.93279*

*Table adapted from [65] with inputs from [64, 66].*

*wood production is the overall major objective.*

**Minimum Harvest Diameter (MHDs):** the most widely applied system and is based only in natural forest production and is considered a "passive" approach (see Section 4.3.1 for further details).

*a*

**Table 2.**


*Table adapted from [65] with inputs from [64, 66].*

*a This grouping of silvicultural systems is presented based on practical experiences, results of applied research or based on the analysis of the ecological conditions of forests that would make a particular system applicable. In all cases, wood production is the overall major objective.*

#### **Table 2.**

*Silviculture*

**Direct transformation (clearcutting)**: system that involves the complete replacement at once of the logged uneven-aged forest by another regular and homogeneous stand, established by even-aged plantation and usually with fast growing species.

**Enrichment in transversal strips**: system of indirect transformation by introducing artificial regeneration *via* strip planting after selective logging mostly to increase commercial stocking of stands. Aims at maintaining the uneven-aged condition of the forest (**Figure 5**).

**Modified selection thinning**: system that seeks to transform a stand with an irregular structure and heterogeneous composition (e.g. 40–70 species/ha) to a more regular and less diverse stand (e.g. 20–30 species/ha).

**Strip clearcuttings**: regeneration system applied to natural tropical forests to transform their heterogeneous structure to a more regular and less diverse

structure.

**Enhanced natural regeneration in strips:** indirect transformation system to promote the establishment of the natural regeneration of valuable species (usually scarce) in previously open strips.

**Silvicultural systema Reasons for its implementation Region or area of the country** 

• Forests poor in abundance of commercially valuable species (young or mature; logged or unlogged); • As a market need, to produce wood for homogeneous products; • Hardly applied today for environ-

• Young or mature forests poor in abundance of commercial species; • Rich or relatively rich forests in which commercial species have limited natural regeneration; • Introduction of one or more species at special demand of an ecological, industrial or market nature;

• Suitable for the permanent treatment of mature natural forests where most of the species are shade tolerant with good natural

• System suitable for forests located on land with moderate to strong slopes prone to erosion that also

• It has been suggested for primary or secondary forests (young or mature) where commercial species are predominately shade-intolerant species with abundant low-weight

• It could be used for relatively regular and homogeneous forests where natural regeneration is high

• Mature forests relatively rich in commercial species with limited natural regeneration to ensure long-

(e.g. Mangroves);

term production;

regeneration;

meet the above;

seeds;

mental reasons.

**where it is applied or may be applicable and main species** 

• Used to be part of the "Active management" scheme applied in the Western Plains by using species such as *Tectona grandis, Gmelina arborea,* and other

• Applicable in the context of fast-growing plantations.

• **Western Plains**: A local version of this system known as "Método Caimital" was developed with positive results. Species used: *Bombacopsis quinata, Cordia apurensis, Handroanthus rosea, Swietenia macrophylla, Cedrela odorata*; • **Guiana Shield**: Mureillo *Erisma uncinatum, Carapa guianensis, Tabebuia serratifolia*;

• **Orinoco Delta:** *Euterpe* 

• Applicable to irregular and heterogeneous forests. A large area of forests in the country meet these conditions, but no information is known about its practical application;

• In the early 1970s this system was applied in a management plan for flooded forests of the Orinoco Delta (Guarapiche Forest Reserve – **Figure 3**) dominated mainly by *Rhizophora mangle.*

• Applied at research scale in Caparo Forest Reserve ("Metodo Limba-Caparo) in the Western Plains with promising results for two important commercial species: *Cedrela odorata* and *Handroanthus* 

*rosea.*

*oleracea*;

exotic species;

**used**

**10**

*Silvicultural systems applied or potentially applicable in Venezuela's production forests.*

management system in terms of the spectrum of commercial species and the relatively low number of trees logged that is common in many tropical managed forests (1–20 trees per ha -[67]). Under these conditions, it was expected that with a proper planning with minimum standards for cutting and transportation activities, the impacts on the forest stand would be low and facilitate a consistent flow of timber in the next cutting cycles [20, 51, 64]. This system was the fundamental basis of the first forest harvesting permits granted in Venezuela more than 40 years ago [23], and remained relatively unaltered even at times when research evidences made clear that major modifications to this approach were urgent in support of long-term sustainable management [44, 68–70].

Most frequently, these MHDs are set by national authorities, and depending on the species groups and their commercial value, values are typically within the range of 30 up to 70 cm or more in diameter at breast height (DBH) [64]. However, these limits are mostly set to accommodate processing technologies and market demands, rather than the biology and persistence of the harvested species, limiting the possibility to provide ecologically sustainable forest management [71]. Remarkably high numbers of species that are common in many tropical differ in growth requirements, growth rates, marketability, ecological roles and other relevant traits. Thus, simple silvicultural guidelines such as fixed MHDs or cutting cycles are unlikely to be satisfactory [13]. In Venezuela's case, the lack of sound ecological information on growth patterns of commercial species, density and structure, along with limited long-term information has been highlighted as a major limitation [23, 24, 69, 72]. A relatively new official regulation related to MHDs enacted in 2009 [73] aimed at solving, at least partly, the lack of data on species growth by expanding the information on the number of species with MHDs. However, if no improvement is made to the overall process of forest planning, including the urgent implementation of reduced impact logging, and a rethinking of cutting cycles the negative perception towards timber harvest is likely to persist (**Figure 4**).

#### *4.3.2 Post-logging silvicultural treatments*

In many tropical managed forests, a group of standard practices are often applied after selective logging to reduce competition for future harvestable trees. These intermediate treatments might include *refining*, that is, the elimination of undesirable tree species or sick or damaged material, to the extent only that the

#### **Figure 4.**

*General conditions of current logging practices in Venezuela's production forests in the Guiana shield. Unplanned road systems are major drivers of forest degradation. By using a RIL approach, the extension and size of logging roads is considerably lower compared to conventional harvesting which ultimately reduces the environmental impacts [55]. Photo: Emilio Vilanova.*

### **Figure 5.**

*Two examples of enrichment planting in strips in the Venezuelan Guiana shield. In less than 10% of the logged stands, strips of 5–6 m in width separated by 40–50 m are opened via clearcutting to establish artificial regeneration of commercial species. In these two examples, the main species planted is* Carapa guianensis *(Meliaceae). Photos: Emilio Vilanova.*

**13**

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects…*

structural stability of the stand is not weakened [64]. Also, *liberation* or the favoring of all valuable individuals (juveniles, candidates) through the elimination of competitors can be part of the silvicultural prescription. In practice, these activities can comprise cutting of vines and/or climbers – even before logging as a step for RIL – and the elimination of undesirable trees that might delay the establishment of regeneration of commercial species after harvest [66]. It is expected that with a periodical repetition and adequate monitoring, these practices would serve as complementary practices within the MHDs system. This approach has been known in Venezuela as *Management of the remnant stand* and was used mostly to improve growing conditions of the advanced regeneration of commercial species with diameters above 15 cm [74]. In some cases, to reduce multiple re-entries, girdling and occasionally poisoning of undesired trees with an arboricide were used [52]. However, although there are positive examples with regards to improving stand growth [e.g. 22], in the few cases where information was available from management plans in Venezuela, girdling often did not helped killing all selected trees and the use of chemicals in highly sensitive ecosystems was later discouraged and

ultimately banned by government agencies overseeing these operations.

Results from early assessments that were carried out as part of the Forest

Management Research Program of the Western Plains, and to some extent in the Guiana Shield region as well, led to the conclusion that in order to secure a sustained production of timber over multiple cutting cycles, natural regeneration of commercial species was limited [52]. It was suggested that this was a direct response of the predominately shade-intolerant condition of most commercial species, its reproductive biology and other limiting factors such as dispersion and germination in both undisturbed and logged stands, which drove the plan for practices aiming at the enhancement or improvement of regeneration [63]. Consequently, several alternatives were tested, from "simple" interventions such as the creation of small gaps or canopy openings to promote rapid colonization of natural regeneration of commercial species, to more intensive practices such as strip clearcutting, prescribed burning, and planting (see **Table 2**). For example, a modified version of the well-known uneven-aged system Shelterwood [56, 66] was applied in an experimental setting in the Western Plains and was described as a "promising" system [23, 52, 70] but the lack of an adequate financial analysis prevented this system for its potential application at the management scale [70]. Another variant of enrichment planting where the intensity of intervention was higher was the method known as "Limba-Caparo Method" [52, 63] and was considered as one of the few successful experiences for this type of system [70]. It is a type of plantation in strips where, once the commercial species are extracted via selective logging, often highly abundant palms, lianas and other minor competing vegetation with a diameter below 10 cm are removed to later facilitate the use of prescribed burning to facilitate establishment of natural regeneration. A synthesis of enrichment planting experiments indicates that this method was successful in promoting regeneration of an important local species (i.e. *Handroanthus rosea*) with rapid growth, high survival and adaptability to various environmental conditions, particularly in some flooded zones where growth of other valuable species is limited [63]. While this system was labeled as promising, the complexity behind the initial treatments, along with concerns for the use of fire in semi-dry forests and the potential impacts on biodiversity were major limitations for the application at larger scales.

*4.3.3 Natural and artificial regeneration enhancement systems*

*DOI: http://dx.doi.org/10.5772/intechopen.93279*

#### *Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects… DOI: http://dx.doi.org/10.5772/intechopen.93279*

structural stability of the stand is not weakened [64]. Also, *liberation* or the favoring of all valuable individuals (juveniles, candidates) through the elimination of competitors can be part of the silvicultural prescription. In practice, these activities can comprise cutting of vines and/or climbers – even before logging as a step for RIL – and the elimination of undesirable trees that might delay the establishment of regeneration of commercial species after harvest [66]. It is expected that with a periodical repetition and adequate monitoring, these practices would serve as complementary practices within the MHDs system. This approach has been known in Venezuela as *Management of the remnant stand* and was used mostly to improve growing conditions of the advanced regeneration of commercial species with diameters above 15 cm [74]. In some cases, to reduce multiple re-entries, girdling and occasionally poisoning of undesired trees with an arboricide were used [52]. However, although there are positive examples with regards to improving stand growth [e.g. 22], in the few cases where information was available from management plans in Venezuela, girdling often did not helped killing all selected trees and the use of chemicals in highly sensitive ecosystems was later discouraged and ultimately banned by government agencies overseeing these operations.

#### *4.3.3 Natural and artificial regeneration enhancement systems*

Results from early assessments that were carried out as part of the Forest Management Research Program of the Western Plains, and to some extent in the Guiana Shield region as well, led to the conclusion that in order to secure a sustained production of timber over multiple cutting cycles, natural regeneration of commercial species was limited [52]. It was suggested that this was a direct response of the predominately shade-intolerant condition of most commercial species, its reproductive biology and other limiting factors such as dispersion and germination in both undisturbed and logged stands, which drove the plan for practices aiming at the enhancement or improvement of regeneration [63]. Consequently, several alternatives were tested, from "simple" interventions such as the creation of small gaps or canopy openings to promote rapid colonization of natural regeneration of commercial species, to more intensive practices such as strip clearcutting, prescribed burning, and planting (see **Table 2**). For example, a modified version of the well-known uneven-aged system Shelterwood [56, 66] was applied in an experimental setting in the Western Plains and was described as a "promising" system [23, 52, 70] but the lack of an adequate financial analysis prevented this system for its potential application at the management scale [70].

Another variant of enrichment planting where the intensity of intervention was higher was the method known as "Limba-Caparo Method" [52, 63] and was considered as one of the few successful experiences for this type of system [70]. It is a type of plantation in strips where, once the commercial species are extracted via selective logging, often highly abundant palms, lianas and other minor competing vegetation with a diameter below 10 cm are removed to later facilitate the use of prescribed burning to facilitate establishment of natural regeneration. A synthesis of enrichment planting experiments indicates that this method was successful in promoting regeneration of an important local species (i.e. *Handroanthus rosea*) with rapid growth, high survival and adaptability to various environmental conditions, particularly in some flooded zones where growth of other valuable species is limited [63]. While this system was labeled as promising, the complexity behind the initial treatments, along with concerns for the use of fire in semi-dry forests and the potential impacts on biodiversity were major limitations for the application at larger scales.

*Silviculture*

**Figure 4.**

*environmental impacts [55]. Photo: Emilio Vilanova.*

*General conditions of current logging practices in Venezuela's production forests in the Guiana shield. Unplanned road systems are major drivers of forest degradation. By using a RIL approach, the extension and size of logging roads is considerably lower compared to conventional harvesting which ultimately reduces the* 

*Two examples of enrichment planting in strips in the Venezuelan Guiana shield. In less than 10% of the logged stands, strips of 5–6 m in width separated by 40–50 m are opened via clearcutting to establish artificial regeneration of commercial species. In these two examples, the main species planted is* Carapa guianensis

**12**

**Figure 5.**

*(Meliaceae). Photos: Emilio Vilanova.*

#### *Silviculture*

Although several variants of this system were tested, it was the simpler versions of enrichment practices with artificial regeneration the ones that were predominately adopted at industrial scales. In fact, these ultimately became a requirement for the approval of many forest management plans in the country's production forests. It was considered a relatively simple approach yet with high environmental impacts [75] especially in highly sensitive ecosystems such as the Guiana Shield. Between 1987 and 2010 a total of 41,460 ha of enrichment strips were planted in Venezuela's production forests [76]. Furthermore, poor adaptability of many of the species used and lack of a solid monitoring plan led to very low growth rates and low survival [62] (**Table 3**). From the commercial standpoint, one of the few economic analyses conducted in Venezuela about the


#### **Table 3.**

*Results from multiple assessments of enrichment planting practices applied in managed forests of the Venezuelan Guiana shield region.*

**15**

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects…*

use of enrichment planting indicate that, even in scenarios of relatively high prices for timber, the net benefit–cost ratio (BCR) was very low, amidst the initial high costs of establishment and long cutting cycles needed to obtain reasonable wood volumes [74]. For many of these reasons, this practice has been officially abandoned, at least as a requirement for the approval of management plans since 2010. Nevertheless, as has been documented in other tropical regions, in recent years there has been a reawakening interest for the use of enrichment planting in a context of restoration of degraded and secondary forests [13, 63, 77]

**5. Overcoming the barriers and limitations of silviculture**

silviculture could be applied in natural tropical forests in Venezuela.

The main product of more than four decades of silvicultural experience in Venezuela is perhaps the existence of an enormous amount of information available on the main silvicultural practices applied or with potential to be applied to natural forests in the country. Most, if not all, this information came from a pioneer effort starting during the early 1970s in support of the idea that natural tropical forests can be sustainably managed and reduce the risk of deforestation. Important elements on the basic ecology of commercial tree species and how these could be managed occupied a major proportion of this process. Yet, the capacity to fully influence

Adequate communication has proven to be an urgent capacity that many scientists are acquiring as a matter to (successfully) transmit sound scientific information to the public and decision makers [78]. Despite this, a weak connection between science, policy and decision-making has been cited multiple times as a major limitation for sustainable management of tropical forests [13]. In terms of silviculture for instance, a limited adoption of some of the recommended systems at commercial scales can be attributed to some extent to failures of researchers to appropriately design their studies, or because some of these interventions are cost prohibitive and these implications are not properly considered during research, which ultimately reflects a failure to communicate their results effectively [13]. This requires an effort to invest resources in training and capacity development into novel approaches to further improve how scientists disseminate the results of research. This is particularly relevant in the context of the current complex political and economic crisis in Venezuela where research

Another element linked to how silvicultural research is conducted has to do with the need to adapt to the recent shifts in the conditions and requirements for sustainable use of tropical forests. While timber production can - and should -continue

In this chapter we have tried to synthetize some of the most important aspects of the silvicultural practices applied in Venezuela's natural production forests. Details on past and current practices and their impacts were offered with the idea of facilitating a much needed discussion about the compatibility of silviculture for enhanced timber production with the maintenance of other ecosystem services offered by tropical managed forests [18, 22]. In doing so, we made a thorough review of the available literature, most of which came in the form of gray literature produced by government agencies, academic institutions, forest companies and other sources. This last section aims at identifying relevant lessons learned over the course of 40+ years including a set of major recommendations to improve how

*DOI: http://dx.doi.org/10.5772/intechopen.93279*

where this approach seems more feasible.

**5.1 The role of scientific research**

forest management at industrial scales was limited.

institutions are being disproportionally affected [79].

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects… DOI: http://dx.doi.org/10.5772/intechopen.93279*

use of enrichment planting indicate that, even in scenarios of relatively high prices for timber, the net benefit–cost ratio (BCR) was very low, amidst the initial high costs of establishment and long cutting cycles needed to obtain reasonable wood volumes [74]. For many of these reasons, this practice has been officially abandoned, at least as a requirement for the approval of management plans since 2010. Nevertheless, as has been documented in other tropical regions, in recent years there has been a reawakening interest for the use of enrichment planting in a context of restoration of degraded and secondary forests [13, 63, 77] where this approach seems more feasible.

#### **5. Overcoming the barriers and limitations of silviculture**

In this chapter we have tried to synthetize some of the most important aspects of the silvicultural practices applied in Venezuela's natural production forests. Details on past and current practices and their impacts were offered with the idea of facilitating a much needed discussion about the compatibility of silviculture for enhanced timber production with the maintenance of other ecosystem services offered by tropical managed forests [18, 22]. In doing so, we made a thorough review of the available literature, most of which came in the form of gray literature produced by government agencies, academic institutions, forest companies and other sources. This last section aims at identifying relevant lessons learned over the course of 40+ years including a set of major recommendations to improve how silviculture could be applied in natural tropical forests in Venezuela.

#### **5.1 The role of scientific research**

*Silviculture*

*Enterolobium cyclocarpum*

*Handroanthus serratifolia*

*Table adapted from [13].*

*Venezuelan Guiana shield region.*

Although several variants of this system were tested, it was the simpler versions of enrichment practices with artificial regeneration the ones that were predominately adopted at industrial scales. In fact, these ultimately became a requirement for the approval of many forest management plans in the country's production forests. It was considered a relatively simple approach yet with high environmental impacts [75] especially in highly sensitive ecosystems such as the Guiana Shield. Between 1987 and 2010 a total of 41,460 ha of enrichment strips were planted in Venezuela's production forests [76]. Furthermore, poor adaptability of many of the species used and lack of a solid monitoring plan led to very low growth rates and low survival [62] (**Table 3**). From the commercial standpoint, one of the few economic analyses conducted in Venezuela about the

**Species Survival (%) Height growth (m/year) Diameter growth (cm/year)**

26.0 0.4 0.82

83.3 0.5 0.62

*Jacaranda copaia* 40.0 1.1 1.36 *Parkia nitida* 79.4 0.8 1.23 *Loxopterygium sagotii* 66.2 0.9 1.16 *Ceiba pentandra* 42.2 0.5 1.13 *Simarouba amara* 75.6 1.1 1.07 *Spondias mombin* 97.5 1.0 0.98 *Cordia spp*. 62.3 0.6 0.92 *Terminalia amazonia* 64.8 0.5 0.89 *Swietenia macrophylla* 54.7 0.5 0.84

*Cedrela odorata* 62.2 0.6 0.75 *Handroanthus rosea* 29.0 0.4 0.69 *Gmelina arborea* 100.0 1.0 0.68 *Pera glabrata* 42.6 0.8 0.65 *Carapa guianensis* 74.3 0.6 0.64 *Caesalpinia coriaria* 77.1 0.3 0.62

*Anacardium giganteum* 93.5 0.8 0.62 *Hymenaea courbaril* 84.6 0.6 0.58 *Erisma uncinatum* 47.2 0.5 0.54 *Cattostema comune* 43.0 0.5 0.48 *Manilkara bidentata* 69.4 0.4 0.48 *Diplotropis purpurea* 29.2 0.3 — *Mouriri huberi* 12.5 0.1 — *Anacardium excelsum* 33.3 0.2 — *Platymiscium pinnatum* — 0.8 — *Samanea saman* 41.1 0.3 — *Tectona grandis* 25.0 0.1 — *Peltogyne porphyrocardia* 63.1 0.4 — **Mean 66.7 0.60 0.80**

*Results from multiple assessments of enrichment planting practices applied in managed forests of the* 

**14**

**Table 3.**

The main product of more than four decades of silvicultural experience in Venezuela is perhaps the existence of an enormous amount of information available on the main silvicultural practices applied or with potential to be applied to natural forests in the country. Most, if not all, this information came from a pioneer effort starting during the early 1970s in support of the idea that natural tropical forests can be sustainably managed and reduce the risk of deforestation. Important elements on the basic ecology of commercial tree species and how these could be managed occupied a major proportion of this process. Yet, the capacity to fully influence forest management at industrial scales was limited.

Adequate communication has proven to be an urgent capacity that many scientists are acquiring as a matter to (successfully) transmit sound scientific information to the public and decision makers [78]. Despite this, a weak connection between science, policy and decision-making has been cited multiple times as a major limitation for sustainable management of tropical forests [13]. In terms of silviculture for instance, a limited adoption of some of the recommended systems at commercial scales can be attributed to some extent to failures of researchers to appropriately design their studies, or because some of these interventions are cost prohibitive and these implications are not properly considered during research, which ultimately reflects a failure to communicate their results effectively [13]. This requires an effort to invest resources in training and capacity development into novel approaches to further improve how scientists disseminate the results of research. This is particularly relevant in the context of the current complex political and economic crisis in Venezuela where research institutions are being disproportionally affected [79].

Another element linked to how silvicultural research is conducted has to do with the need to adapt to the recent shifts in the conditions and requirements for sustainable use of tropical forests. While timber production can - and should -continue

being an objective in the management of production forests, the contribution of other elements such as non-timber forest products or ecosystems services including biodiversity conservation and mitigation of climate change must be part of any research agenda for a twenty-first century silviculture. Furthermore, research on topics beyond logging practices is needed to assure both sustainability and that these other values are not underestimated and unnecessarily compromised where timber production is the principal goal of management [13].

#### **5.2 A need for better monitoring**

Appropriate technical procedures for monitoring the process of forest management are critical to decision-making. While this goes beyond silvicultural practices, many of the treatments applied in Venezuela's production forests were insufficiently monitored or never monitored at all. The implications of this might be two-fold. On one hand, the absence of standard guidelines for monitoring could have severely limited the real potential for some of the most promising practices (e.g. "Caimital" enrichment system) or, on the other, could have helped in abandoning more quickly those that clearly showed negative results (e.g. forest conversion of logged forests). For a country with a silvicultural research program that started more than four decades ago, and with one of the oldest forestry schools in the tropics, it is remarkable that not a single formal process of forest monitoring has been part of the national forest policy. Examples such as the guidelines developed by the International Tropical Timber Organization (ITTO) [80] have been largely underestimated and can serve as a guide for the adoption of criteria and indicators for monitoring forest management including silvicultural practices.

#### **5.3 Amplifying the objectives of silviculture**

The need for a different perspective in silvicultural practices was previously addressed in item 5.1 when analyzing the role of scientific research. However, from the standpoint of policy and decision making, it is important to reinforce the idea that if we want to preserve the vast amount of production forests still available, a new vision of silviculture should be adopted. In many tropical regions, logged forests often retain substantial biodiversity, carbon and timber stocks [18]. Thus, increasing the overall value of production forests in the tropics compared to other more intensive land-uses often highly profitable and linked to deforestation [81] is not only a matter of applying reduced impact logging practices – although urgently needed in Venezuela [45]. It also requires major modifications to integrate the great diversity of products that can be obtained from these ecosystems. In this process, at least in the short and medium terms, updating forest education curriculum programs at different levels and directly connected to applied forestry practices can contribute to the formulation of new strategies for diversifying forest management [82]. Assessments of non-timber forest products to design silvicultural practices [83], use of silviculture for ecological restoration [64], or simply improving harvesting practices as a tool to mitigate climate change and conserve biological diversity [84] are all important steps towards a more inclusive practice of forest management.

#### **6. Final remarks and conclusions**

Venezuela has now more than 40 years of experience in the development of forestry practices for the country's forests, plantations and other forest lands, a long-term valued effort for the forestry sector in the tropical region and in Latin

**17**

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects…*

America. The development of a conceptual and practical model for the management of the country's natural forests and the establishment of a significant area of forest plantations are all remarkable actions. However, available information reviewed here clearly indicates that the objectives originally set out primarily to increase forest productivity were not achieved. In addition, the negative environmental effects of timber harvest have been significant, and the overall role of management as has been applied up to now in the country's production forests should be questioned. While multiple drivers interacted, the total loss of most production forests in the Western Plains, the reduction in recent years of the area with formal management plans, and the limited participation of local communities in the practice and benefits of forest management, among others, indicate the urgent need

While further analysis is required for additional technical details about the characteristics of the silvicultural practices applied in Venezuela, the main goal of this chapter was, first of all, to provide an historical perspective for one of the countries with the richest, yet largely unknown, silvicultural experience in the tropical region. Secondly, understanding the historical reasons that led to the design and implementation of the different forest management strategies in much of the country's forests, helps identifying the benefits, advantages and the limitations to improve the practice of silviculture in Venezuela's natural production forests. Despite the loss of some of the most productive ecosystems in the Western Plains, the existence of an important resource base for forest production, especially in the Guiana Shield region from which a large proportion of rural populations depends, represents a great opportunity for improving forest management based on prin-

Finally, the institutional and political changes that started in the early 2000s have undoubtedly impacted how forests resources have been managed in the last 20 years. From the concession model in the late 1990s, dominated by private companies often poorly managed with a very low degree of compliance to sustainable management guidelines, management of natural production forests slowly shifted towards a heavily government-dominated system. This transition included a general revision of how silviculture should be applied but the expected outcomes for a new and more sustainable model are far from being clear. Furthermore, the ongoing political and socioeconomic crisis in the country is putting at risk the long-term stability of many natural production forests. We firmly believe that these changes, if widely discussed and agreed upon by all actors involved in forest management, can facilitate the adoption of better practices and thus increase the strategic value of

This chapter is the result of a regional project led by FAO's forestry office to conduct a review of silvicultural practices in Amazonian countries. Thus, the author first wants to express his gratitude to Dr. César Sabogal from FAO for coordinating the project and for the useful comments and suggestions throughout the entire process. Many thanks to all the staff of the Venezuelan government agencies, in particular to Américo Catalán, Luis Sulbarán, José Ignacio Azuaje and Edgar Quintero for granting access to many of the official reports and statistics. To all the people who contributed with ideas and suggestions during the surveys that were sent out during the preparation of the original report. Finally, special thanks to Dr. Carlos Pacheco from Universidad de Los Andes in Venezuela who helped creating the map in **Figure 3**. This publication made possible in part by support from the Berkeley Research

*DOI: http://dx.doi.org/10.5772/intechopen.93279*

ciples of multiple use of forests.

**Acknowledgements**

to reformulate how Venezuelan forests have been managed.

forests as tools for the sustainable development of the country.

#### *Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects… DOI: http://dx.doi.org/10.5772/intechopen.93279*

America. The development of a conceptual and practical model for the management of the country's natural forests and the establishment of a significant area of forest plantations are all remarkable actions. However, available information reviewed here clearly indicates that the objectives originally set out primarily to increase forest productivity were not achieved. In addition, the negative environmental effects of timber harvest have been significant, and the overall role of management as has been applied up to now in the country's production forests should be questioned. While multiple drivers interacted, the total loss of most production forests in the Western Plains, the reduction in recent years of the area with formal management plans, and the limited participation of local communities in the practice and benefits of forest management, among others, indicate the urgent need to reformulate how Venezuelan forests have been managed.

While further analysis is required for additional technical details about the characteristics of the silvicultural practices applied in Venezuela, the main goal of this chapter was, first of all, to provide an historical perspective for one of the countries with the richest, yet largely unknown, silvicultural experience in the tropical region. Secondly, understanding the historical reasons that led to the design and implementation of the different forest management strategies in much of the country's forests, helps identifying the benefits, advantages and the limitations to improve the practice of silviculture in Venezuela's natural production forests. Despite the loss of some of the most productive ecosystems in the Western Plains, the existence of an important resource base for forest production, especially in the Guiana Shield region from which a large proportion of rural populations depends, represents a great opportunity for improving forest management based on principles of multiple use of forests.

Finally, the institutional and political changes that started in the early 2000s have undoubtedly impacted how forests resources have been managed in the last 20 years. From the concession model in the late 1990s, dominated by private companies often poorly managed with a very low degree of compliance to sustainable management guidelines, management of natural production forests slowly shifted towards a heavily government-dominated system. This transition included a general revision of how silviculture should be applied but the expected outcomes for a new and more sustainable model are far from being clear. Furthermore, the ongoing political and socioeconomic crisis in the country is putting at risk the long-term stability of many natural production forests. We firmly believe that these changes, if widely discussed and agreed upon by all actors involved in forest management, can facilitate the adoption of better practices and thus increase the strategic value of forests as tools for the sustainable development of the country.

#### **Acknowledgements**

This chapter is the result of a regional project led by FAO's forestry office to conduct a review of silvicultural practices in Amazonian countries. Thus, the author first wants to express his gratitude to Dr. César Sabogal from FAO for coordinating the project and for the useful comments and suggestions throughout the entire process. Many thanks to all the staff of the Venezuelan government agencies, in particular to Américo Catalán, Luis Sulbarán, José Ignacio Azuaje and Edgar Quintero for granting access to many of the official reports and statistics. To all the people who contributed with ideas and suggestions during the surveys that were sent out during the preparation of the original report. Finally, special thanks to Dr. Carlos Pacheco from Universidad de Los Andes in Venezuela who helped creating the map in **Figure 3**. This publication made possible in part by support from the Berkeley Research

*Silviculture*

being an objective in the management of production forests, the contribution of other elements such as non-timber forest products or ecosystems services including biodiversity conservation and mitigation of climate change must be part of any research agenda for a twenty-first century silviculture. Furthermore, research on topics beyond logging practices is needed to assure both sustainability and that these other values are not underestimated and unnecessarily compromised where

Appropriate technical procedures for monitoring the process of forest management are critical to decision-making. While this goes beyond silvicultural practices, many of the treatments applied in Venezuela's production forests were insufficiently monitored or never monitored at all. The implications of this might be two-fold. On one hand, the absence of standard guidelines for monitoring could have severely limited the real potential for some of the most promising practices (e.g. "Caimital" enrichment system) or, on the other, could have helped in abandoning more quickly those that clearly showed negative results (e.g. forest conversion of logged forests). For a country with a silvicultural research program that started more than four decades ago, and with one of the oldest forestry schools in the tropics, it is remarkable that not a single formal process of forest monitoring has been part of the national forest policy. Examples such as the guidelines developed by the International Tropical Timber Organization (ITTO) [80] have been largely underestimated and can serve as a guide for the adoption of criteria and indicators

timber production is the principal goal of management [13].

for monitoring forest management including silvicultural practices.

The need for a different perspective in silvicultural practices was previously addressed in item 5.1 when analyzing the role of scientific research. However, from the standpoint of policy and decision making, it is important to reinforce the idea that if we want to preserve the vast amount of production forests still available, a new vision of silviculture should be adopted. In many tropical regions, logged forests often retain substantial biodiversity, carbon and timber stocks [18]. Thus, increasing the overall value of production forests in the tropics compared to other more intensive land-uses often highly profitable and linked to deforestation [81] is not only a matter of applying reduced impact logging practices – although urgently needed in Venezuela [45]. It also requires major modifications to integrate the great diversity of products that can be obtained from these ecosystems. In this process, at least in the short and medium terms, updating forest education curriculum programs at different levels and directly connected to applied forestry practices can contribute to the formulation of new strategies for diversifying forest management [82]. Assessments of non-timber forest products to design silvicultural practices [83], use of silviculture for ecological restoration [64], or simply improving harvesting practices as a tool to mitigate climate change and conserve biological diversity [84] are all important steps towards a more inclusive practice of forest management.

Venezuela has now more than 40 years of experience in the development of forestry practices for the country's forests, plantations and other forest lands, a long-term valued effort for the forestry sector in the tropical region and in Latin

**5.3 Amplifying the objectives of silviculture**

**6. Final remarks and conclusions**

**5.2 A need for better monitoring**

**16**

Impact Initiative (BRII) sponsored by the University of California Berkeley Library. Special thanks to Dr. Hirma Ramírez-Angulo and Dr. Armando Torres-Lezama from Universidad de Los Andes for their support during this research project.

### **Conflict of interest**

The author declares no conflict of interest.

### **Author details**

Emilio Vilanova Department of Environmental Science, Policy, and Management, University of California, Berkeley, USA

\*Address all correspondence to: evilanova@berkeley.edu

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**19**

Series; 2011

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects…*

2015;**4**(1):1-7

[10] Sist P, Rutishauser E,

[11] Piponiot C, Rutishauser E, Derroire G, Putz FE, Sist P, West TAP, et al. Optimal strategies for ecosystem services provision in Amazonian production forests. Environmental Research Letters. 2019;**14**(6):64014. DOI: 10.1088/1748-9326/ab195e

[12] Piponiot C, Rödig E, Putz FE, Rutishauser E, Sist P, Ascarrunz N, et al. Can timber provision from Amazonian

[13] Putz FE, Romero C. Futures of tropical production forests. In: Futures

Occasional Paper 143. Bogor, Indonesia: Center for International Forestry Research (CIFOR); 2015. p. 51. DOI:

[14] Hérault B, Piponiot C. Key drivers of ecosystem recovery after disturbance in a neotropical forest: Long-term lessons from the Paracou experiment, French Guiana. Forest Ecosystems.

[15] Rutishauser E, Hérault B, Baraloto C, Blanc L, Descroix L, Sotta ED, et al. Rapid tree carbon stock recovery in managed Amazonian forests. Current Biology. 2015;**25**(18):

R787-R788. DOI: 10.1016/j.

of Tropical Production Forests.

10.17528/cifor/005766

2018;**5**(1):1-15

cub.2015.07.034

natural forests be sustainable? Environmental Research Letters. 2019;**14**(12):124090. DOI: 10.1088/1748-9326/ab5eb1

2015;**18**(1):171-174

production forests. A systematic review protocol. Environmental Evidence.

Peña-Claros M, Shenkin A, Hérault B, Blanc L, et al. The tropical managed forests observatory: A research network addressing the future of tropical logged forests. Applied Vegetation Science.

*DOI: http://dx.doi.org/10.5772/intechopen.93279*

[1] FAO. The State of the World's Forests.

[2] Beer C, Reichstein M, Tomelleri E, Ciais P, Jung M, Carvalhais N, et al. Terrestrial gross carbon dioxide uptake:

covariation with climate. Science.

[3] Mitchard ETA. The tropical forest carbon cycle and climate change. Nature. 2018;**559**(7715):527-534. DOI:

[4] Le QC, Andrew RM, Canadell JG, Sitch S, Korsbakken JI, Peters GP, et al. Global carbon budget. Earth System Science Data. 2016;**2016**:605-649

[5] FAO-UNEP. The State of the World's Forests 2020 [Internet]. Rome: Food and Agriculture Organization of the United Nations; 2020. p. 139. Available from: http://www.fao.org/documents/card/

Moore R, Hancher M, Turubanova SA, Tyukavina A, et al. High-resolution

[7] Baccini A, Walker W, Carvalho L, Farina M, Houghton RA. Tropical forests are a net carbon source based on aboveground measurements of gain and loss. Science. 2017;**358**(6360):230-234

[8] Blaser J, Sarre A, Poore D, Johnson S. Status of Tropical Forest Management 2011. Yokohama, Japan: ITTO Technical

[9] Petrokofsky G, Sist P, Blanc L, Doucet JL, Finegan B, Gourlet-Fleury S, et al. Comparative effectiveness of silvicultural interventions for increasing timber production and sustaining conservation values in natural tropical

Rome: FAO; 2018. p. 118

**References**

Global distribution and

2010;**329**(5993):834-838

10.1038/s41586-018-0300-2

en/c/ca8642en

[6] Hansen MC, Potapov PV,

global maps of 21st-century forest cover change. Science. 2013;**342**(6160):850-853

*Silvicultural Practices in Venezuelan Natural Forests: An Historical Perspective and Prospects… DOI: http://dx.doi.org/10.5772/intechopen.93279*

#### **References**

*Silviculture*

**Conflict of interest**

**18**

**Author details**

Emilio Vilanova

California, Berkeley, USA

Department of Environmental Science, Policy, and Management, University of

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Impact Initiative (BRII) sponsored by the University of California Berkeley Library. Special thanks to Dr. Hirma Ramírez-Angulo and Dr. Armando Torres-Lezama from

Universidad de Los Andes for their support during this research project.

The author declares no conflict of interest.

\*Address all correspondence to: evilanova@berkeley.edu

provided the original work is properly cited.

[1] FAO. The State of the World's Forests. Rome: FAO; 2018. p. 118

[2] Beer C, Reichstein M, Tomelleri E, Ciais P, Jung M, Carvalhais N, et al. Terrestrial gross carbon dioxide uptake: Global distribution and covariation with climate. Science. 2010;**329**(5993):834-838

[3] Mitchard ETA. The tropical forest carbon cycle and climate change. Nature. 2018;**559**(7715):527-534. DOI: 10.1038/s41586-018-0300-2

[4] Le QC, Andrew RM, Canadell JG, Sitch S, Korsbakken JI, Peters GP, et al. Global carbon budget. Earth System Science Data. 2016;**2016**:605-649

[5] FAO-UNEP. The State of the World's Forests 2020 [Internet]. Rome: Food and Agriculture Organization of the United Nations; 2020. p. 139. Available from: http://www.fao.org/documents/card/ en/c/ca8642en

[6] Hansen MC, Potapov PV, Moore R, Hancher M, Turubanova SA, Tyukavina A, et al. High-resolution global maps of 21st-century forest cover change. Science. 2013;**342**(6160):850-853

[7] Baccini A, Walker W, Carvalho L, Farina M, Houghton RA. Tropical forests are a net carbon source based on aboveground measurements of gain and loss. Science. 2017;**358**(6360):230-234

[8] Blaser J, Sarre A, Poore D, Johnson S. Status of Tropical Forest Management 2011. Yokohama, Japan: ITTO Technical Series; 2011

[9] Petrokofsky G, Sist P, Blanc L, Doucet JL, Finegan B, Gourlet-Fleury S, et al. Comparative effectiveness of silvicultural interventions for increasing timber production and sustaining conservation values in natural tropical

production forests. A systematic review protocol. Environmental Evidence. 2015;**4**(1):1-7

[10] Sist P, Rutishauser E, Peña-Claros M, Shenkin A, Hérault B, Blanc L, et al. The tropical managed forests observatory: A research network addressing the future of tropical logged forests. Applied Vegetation Science. 2015;**18**(1):171-174

[11] Piponiot C, Rutishauser E, Derroire G, Putz FE, Sist P, West TAP, et al. Optimal strategies for ecosystem services provision in Amazonian production forests. Environmental Research Letters. 2019;**14**(6):64014. DOI: 10.1088/1748-9326/ab195e

[12] Piponiot C, Rödig E, Putz FE, Rutishauser E, Sist P, Ascarrunz N, et al. Can timber provision from Amazonian natural forests be sustainable? Environmental Research Letters. 2019;**14**(12):124090. DOI: 10.1088/1748-9326/ab5eb1

[13] Putz FE, Romero C. Futures of tropical production forests. In: Futures of Tropical Production Forests. Occasional Paper 143. Bogor, Indonesia: Center for International Forestry Research (CIFOR); 2015. p. 51. DOI: 10.17528/cifor/005766

[14] Hérault B, Piponiot C. Key drivers of ecosystem recovery after disturbance in a neotropical forest: Long-term lessons from the Paracou experiment, French Guiana. Forest Ecosystems. 2018;**5**(1):1-15

[15] Rutishauser E, Hérault B, Baraloto C, Blanc L, Descroix L, Sotta ED, et al. Rapid tree carbon stock recovery in managed Amazonian forests. Current Biology. 2015;**25**(18): R787-R788. DOI: 10.1016/j. cub.2015.07.034

[16] Puettmann KJ, Coates KD, Messier C. A Critique of Silviculture: Managing for Complexity. Washington D.C: Island Press; 2009. p. 207

[17] Fahey RT, Alveshere BC, Burton JI, D'Amato AW, Dickinson YL, Keeton WS, et al. Shifting conceptions of complexity in forest management and silviculture. Forest Ecology and Management. 2018;**421**(January):59-71

[18] Putz FE, Zuidema PA, Synnott T, Peña-Claros M, Pinard MA, Sheil D, et al. Sustaining conservation values in selectively logged tropical forests: The attained and the attainable. Conservation Letters. 2012;**5**(4):296-303

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59672014000200004&lng

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=en&tlng=en

gfw\_venezuela.pdf

Burton JI, D'Amato AW, Dickinson YL, Keeton WS, et al. Shifting conceptions of complexity in forest management and silviculture. Forest Ecology and Management. 2018;**421**(January):59-71

[18] Putz FE, Zuidema PA, Synnott T, Peña-Claros M, Pinard MA, Sheil D, et al. Sustaining conservation values in selectively logged tropical forests: The attained and the attainable.

Conservation Letters. 2012;**5**(4):296-303

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linkinghub.elsevier.com/retrieve/pii/

[20] Dawkins H, Phillip M. Tropical Moist Forest Silviculture and

Management: A History of Successes and Failures. Cambridge, UK: University

[21] Weber M. Review: New aspects in tropical Silviculture. In: Gunter S, Weber M, Stimm B, Mosandl R, editors. Silviculture in the Tropics. Berlin Heidelberg: Springer-Verlag; 2011. pp.

[22] Finegan B. 21st century viewpoint on tropical Silviculture. In: Pancel L, Kohl M, editors. Tropical Forestry Handbook. 2nd ed. Berlin: Springer-Verlag Berlin Heidelberg; 2016. pp. 1605-1638

[23] Kammesheidt L, Lezama AT, Franco W, Plonczak M. History of logging and silvicultural treatments in

[19] Yguel B, Piponiot C,

S0378112718314944

Press; 1998. p. 351

**20**

63-89

[30] Pacheco-angulo C, Vilanova E, Aguado I, Monjardin S. Carbon emissions from deforestation and degradation in a forest reserve in Venezuela between 1990 and 2015. Forests. 2017;**8**:291. DOI: 10.3390/ f8080291

[31] Aide TM, Grau HR, Graesser J, Andrade-Nuñez MJ, Aráoz E, Barros AP, et al. Woody vegetation dynamics in the tropical and subtropical Andes from 2001 to 2014: Satellite image interpretation and expert validation. Global Change Biology. 2019;**25**(6):2112-2126. DOI: 10.1111/ gcb.14618

[32] Harris NL, Brown S, Hagen SC, Saatchi SS, Petrova S, Salas W, et al. Baseline map of carbon emissions from deforestation in tropical regions. Science. 2012;**336**(6088):1573-1576

[33] Pearson TRH, Brown S, Murray L, Sidman G. Greenhouse gas emissions from tropical forest degradation: An underestimated source. Carbon Balance and Management. 2017;**12**(1):3. DOI: 10.1186/s13021-017-0072-2

[34] Waliser DE, Jiang X. In: North GR, Pyle J, editors. Tropical Meteorology and Climate | Intertropical Convergence Zone. Oxford: Academic Press; 2015. pp. 121-131. Available from: http://www. sciencedirect.com/science/article/pii/ B9780123822253004175

[35] Huber O, Oliveira-Miranda M. Ambientes terrestres de Venezuela. In: Rodríguez J, Rojas-Suárez F, Hernández D, editors. Libro Rojo de los Ecosistemas Terrestres de Venezuela. Caracas: PROVITA, Shell Venezuela, Lenovo Venezuela; 2010. pp. 29-89

[36] Arismendi J. Presentación geográfica de las formas de relieve. In: Fundación Empresas Polar. Caracas,

Venezuela: GeoVenezuela, Tomo 2; 2007. pp. 128-183

[37] Baruch Z. Vegetation–environment relationships and classification of the seasonal savannas in Venezuela. Flora - Morphology Distribution Functional Ecology of Plants. 2005;**200**(1):49- 64. Available from: http://www. sciencedirect.com/science/article/pii/ S036725300500006X

[38] Dourojeanni M. El futuro de los bosques de América Latina. In: Keipi K, editor. Políticas forestales en América Latina. Washington D.C.: Banco Interamericano de Desarrollo (BID); 2000. pp. 89-104

[39] Kammesheidt L. Some autecological characteristics of early to late successional tree species in Venezuela. Acta Oecologica. 2000;**21**(1):37- 48. Available from: https://www. sciencedirect.com/science/article/pii/ S1146609X00001089

[40] Centeno J. Estrategia para el desarrollo forestal en Venezuela. Caracas, Venezuela: Fondo Nacional de Investigación Forestal; 1995. p. 83

[41] del Ambiente M. Anuario de Estadísticas Forestales 2007. Caracas, Venezuela: Ministerio del Ambiente-Venezuela; 2008

[42] MINEC. Anuario Estadísticas Forestales 2017. Caracas, Venezuela: Ministerio del Poder Popular para el Ambiente y el Ecosocialismo-Venezuela; 2018

[43] Aicher C. Los efectos del conocimiento forestal en la política forestal venezolana. In: SEFUT Working Paper No. 14. Freiburg, Germany: Albert-Ludwigs-Universität Freiburg; 2005. p. 39. Available from: https:// freidok.uni-freiburg.de/fedora/objects/ freidok:1747/datastreams/FILE1/content

[44] Lozada JR. Situación actual y perspectivas del manejo de recursos forestales en Venezuela. Revista Forestal Venezolana. 2007;**51**(2):195-218

[45] Vilanova E, Ramírez-Angulo H, Ramírez G, Torres-Lezama A. Compliance with sustainable forest management guidelines in three timber concessions in the Venezuelan Guayana: Analysis and implications. Forest Policy and Economics. 2012;**17**:3-12

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[47] Rojas-López J. Regulación ambiental y colonización agraria en reservas de bosque. El drama de Ticoporo, estado Barinas-Venezuela. Revista Geográfica Venezolana. 2007;**48**(1):129-141

[48] Carrero GO, Andrade V. La contribución de las actividades del sector primario y secundario de la cadena forestal al PIB de Venezuela en los últimos 50 años y su relación con algunas variables macroeconómicas. Revista Forestal Venezolana. 2005;**49**(1):39-47

[49] de Venezuela RB. Ley de Bosques. Caracas, Venezuela: Asamblea Nacional; 2013. Gaceta Oficial No. 403.780

[50] Dawkins H. The Management of Natural Tropical High-Forest with Special Reference to Uganda. Oxford, UK: Imperial Forestry Institute, University of Oxford, Oxford, UK; 1958

[51] Lamprecht H. Silvicultura en los trópicos: Los ecosistemas forestales en los bosques tropicales y sus especies arbóreas -posibilidades y métodos para un aprovechamiento sostenido. Germany: Eschborn; 1990

[52] Vincent L, Rodriguez-Poveda L, Noguera O, Arends E, Lozada J. Evolución histórica, y desarrollos recientes de la silvicultura del Bosque Tropical Alto en América. In: Informe del Seminario-Taller "Experiencias prácticas y prioridades de Investigación en Silvicultura de Bosques Naturales en América Tropical." Pucallpa, Perú. Venezuela: Centro de Estudios Forestales y Ambientales de Postgrado; 1996

[53] Vincent L. A tropical forest minimum impact management system. Bois et Forets des Tropiques. 2004;**279**(1):88-90

[54] Plonczak M, Rodriguez-Poveda L. Conceptos, fundamentos y métodos del manejo forestal en Venezuela. Revista Forestal Venezolana. 2002;**46**(1):83-90

[55] Bicknell JE, Struebig MJ, Davies ZG. Reconciling timber extraction with biodiversity conservation in tropical forests using reduced-impact logging. Journal of Applied Ecology. 2015;**52**(2):379-388

[56] Putz FE. Ruslandi. Intensification of tropical silviculture. Journal of Tropical Forest Science. 2015;**27**(3):285-288

[57] Huth A, Kammesheidt L, Koehler P. Sustainable timber harvesting in Venezuela: A modelling approach. Journal of Applied Ecology. 2001;**38**(4):756-770

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[66] Ashton MS, Kelty M. The Practice of Silviculture: Applied Forest Ecology. 10th ed. Oxford, UK: John Wiley &

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forestales en Venezuela. Revista Forestal

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[53] Vincent L. A tropical forest minimum impact management system. Bois et Forets des Tropiques.

[54] Plonczak M, Rodriguez-Poveda L. Conceptos, fundamentos y métodos del manejo forestal en Venezuela. Revista Forestal Venezolana. 2002;**46**(1):83-90

[55] Bicknell JE, Struebig MJ, Davies ZG. Reconciling timber extraction with biodiversity conservation in tropical forests using reduced-impact logging. Journal of Applied Ecology.

[56] Putz FE. Ruslandi. Intensification of tropical silviculture. Journal of Tropical Forest Science. 2015;**27**(3):285-288

Koehler P. Sustainable timber harvesting in Venezuela: A modelling approach.

[58] Noguera LO, Pacheco AC, Plonczak Ratschiller M, Jeréz RM, Moret A, Quevedo RA, et al. Planificación de la explotación de impacto reducido como base para un manejo forestal sustentable en un sector de la Guayana venezolana. Rev For Venez. 2008;**51**(1):67-78

[59] Lozada JR, Arends E. Impactos ambientales del aprovechamiento forestal en Venezuela. Interciencia.

[60] Vilanova-Torre E, Ramírez-Angulo H, Torres-Lezama A. Carbon storage in the aboveground biomass as indicator of logging impact in the Imataca Forest reserve, Venezuela. Interciencia. 2010;**35**(9):659-665

[57] Huth A, Kammesheidt L,

Journal of Applied Ecology.

2001;**38**(4):756-770

1998;**23**(2):74-83

2004;**279**(1):88-90

2015;**52**(2):379-388

Venezolana. 2007;**51**(2):195-218

and Economics. 2012;**17**:3-12

org/3/a-az372s.pdf

[45] Vilanova E, Ramírez-Angulo H, Ramírez G, Torres-Lezama A. Compliance with sustainable forest management guidelines in three timber concessions in the Venezuelan Guayana: Analysis and implications. Forest Policy

[46] Food and Agriculture Organization of the United Nations. Evaluación de los Recursos Forestales Mundiales 2015 - Informe Nacional Venezuela [Internet]. 2014. Available from: http://www.fao.

[47] Rojas-López J. Regulación ambiental y colonización agraria en reservas de bosque. El drama de Ticoporo, estado Barinas-Venezuela. Revista Geográfica Venezolana. 2007;**48**(1):129-141

contribución de las actividades del sector primario y secundario de la cadena forestal al PIB de Venezuela en los últimos 50 años y su relación con algunas variables macroeconómicas. Revista Forestal Venezolana. 2005;**49**(1):39-47

[49] de Venezuela RB. Ley de Bosques. Caracas, Venezuela: Asamblea Nacional;

[50] Dawkins H. The Management of Natural Tropical High-Forest with Special Reference to Uganda. Oxford, UK: Imperial Forestry Institute,

University of Oxford, Oxford, UK; 1958

[51] Lamprecht H. Silvicultura en los trópicos: Los ecosistemas forestales en los bosques tropicales y sus especies arbóreas -posibilidades y métodos para un aprovechamiento sostenido.

[52] Vincent L, Rodriguez-Poveda L, Noguera O, Arends E, Lozada J. Evolución histórica, y desarrollos recientes de la silvicultura del Bosque

Germany: Eschborn; 1990

2013. Gaceta Oficial No. 403.780

[48] Carrero GO, Andrade V. La

**22**

[62] Lozada JR, Moreno J, Suescun R. Plantaciones de enriquecimiento. Experiencias en 4 unidades de manejo forestal de la Guayana venezolana. Interciencia. 2003;**28**(10):568-575

[63] Jerez-Rico M, Quevedo A, Moret AY, Plonczak M, Garay V, Silva JD, et al. Regeneración natural inducida y plantaciones forestales con especies nativas: potencial y limitaciones para la recuperación de bosques tropicales degradados en los llanos occidentales de Venezuela. In: Herrera F, Herrera I, editors. La Restauración Ecológica en Venezuela: Fundamentos y experiencias. Caracas, Venezuela: Instituto Venezolano de Investigaciones Científicas (IVIC); 2011. pp. 35-60

[64] Pancel L. Technical orientation of Silviculture in the tropics. In: Pancel L, Köhl M, editors. Tropical Forestry Handbook. 2nd ed. Berlin, Germany: Springer-Verlag Berlin Heidelberg; 2016. pp. 1639-1691

[65] Finol H. Sistemas silviculturales aplicados y aplicables al manejo de bosques tropicales en Venezuela. Venezuela: Mérida; 1983

[66] Ashton MS, Kelty M. The Practice of Silviculture: Applied Forest Ecology. 10th ed. Oxford, UK: John Wiley & Sons, Ltd; 2018. p. 776

[67] Burivalova Z, Şekercioǧlu ÇH, Koh LP. Thresholds of logging intensity to maintain tropical forest biodiversity. Current Biology. 2014;**24**(16):1893-1898

[68] Ramirez-Angulo H, Ablan M, Torres-Lezama A, Acevedo MF. Simulación de la dinámica de un bosque tropical en los llanos

occidentales de venezuela. Interciencia. 2006;**31**(2):101-109

[69] D'Jesus A, Torres Lezama A, Ramírez Angulo H. Consecuencias de la explotación maderera sobre el crecimiento y el rendimiento sostenible de un bosque húmedo deciduo en los llanos occidentales de Venezuela. Revista Forestal Venezolana. 2001;**45**:133-143

[70] Torres-Lezama A. La cuidada movilización de los recursos forestales. La industria forestal. In: Pantin A, Reyes A, Quintero A, Montero R, Cunill-Grau P, Márquez A, et al., editors. Geo Venezuela. Caracas, Venezuela: Fundación Empresas Polar; 2007. pp. 382-439

[71] Sist P, Fimbel R, Sheil D, Nasi R, Chevallier MH. Towards sustainable management of mixed dipterocarp forests of Southeast Asia: Moving beyond minimum diameter cutting limits. Environmental Conservation. 2003;**30**(4):364-374

[72] Kammesheidt L. Stand structure and spatial pattern of commercial species in logged and unlogged Venezuelan forest. Forest Ecology and Management. 1998;**109**(1-3):163-174

[73] de Venezuela RB. Norma técnica forestal sobre diámetros mínimos de cortabilidad. Caracas, Venezuela: Asamblea Nacional; 2009. Resolución No. 0000030

[74] Noguera LO, Carrero GO, Plonczak M, Jerez M, Kool G. Evaluación técnica y financiera de la silvicultura desarrollada en un bosque natural de la Guayana venezolana. Bois et Forets des Tropiques. 2007;**290**(4):81-91

[75] Ochoa GJ. Análisis preliminar de los efectos del aprovechamiento de maderas sobre la composición y estructura de bosques en la guayana venezolana. Interciencia. 1998;**23**(4):197-207

[76] Instituto Forestal Latinoamericano (IFLA). Evaluación del sistema silvicultural plantaciones en fajas de enriquecimiento (PFE) en las reservas forestales Imataca, San Pedro y Dorado Tumeremo, estado Bolívar. Mérida, Venezuela: Instituto Forestal Latinoamericano; 2010

[77] Hardt Ferreira dos Santos VA, Modolo GS, Ferreira MJ. How do silvicultural treatments alter the microclimate in a Central Amazon secondary forest? A focus on light changes. Journal of Environmental Management. 2020;**254**(October 2019):109816. Available from: https:// www.sciencedirect.com/science/article/ pii/S0301479719315348?dgcid=author

[78] Kappel K, Holmen SJ. Why science communication, and does it work? A taxonomy of science communication aims and a survey of the empirical evidence. Frontiers in Communication. 2019;**4**:55. Available from: https:// www.frontiersin.org/article/10.3389/ fcomm.2019.00055

[79] Paniz-Mondolfi AE, Rodríguez-Morales AJ. Venezuelan science in dire straits. Science. 2014;**346**(6209):559. Available from: http://science.sciencemag.org/ content/346/6209/559.abstract

[80] International Tropical Timber Organization - ITTO. Criteria and indicators for the sustainable management of tropical forests. ITTO Policy Development Series No. 21. [Internet]. 2016. pp. 1-84. Available from: https://www.itto.int/ direct/topics/topics\_pdf\_download/ topics\_id=4872&no=1&disp=inline

[81] Nepstad D, McGrath D, Stickler C, Alencar A, Azevedo A, Swette B, et al. Slowing Amazon deforestation through public policy and interventions in beef and soy supply chains. Science. 2014;**344**(6188):1118-1123

[82] Guariguata M, Evans K. Advancing tropical forestry curricula through nontimber Forest products. International Forestry Review. 2010;**12**(4):418-426. Available from: http://www.jstor.org/ stable/24309824

[83] Sist P, Sablayrolles P, Barthelon S, Sousa-Ota L, Kibler JF, Ruschel A, et al. The contribution of multiple use forest management to small farmers' annual incomes in the eastern Amazon. Forests. 2014;**5**(7):1508-1531

[84] Griscom BW, Goodman RC, Burivalova Z, Putz FE. Carbon and biodiversity impacts of intensive versus extensive tropical forestry. Conservation Letters. 2018;**11**(1):1-16

**25**

**1. Introduction**

**Chapter 2**

**Abstract**

Mixed Forest Plantations with

Restoration in Cloud Forests of the

Tropical cloud forests play a fundamental role in the hydrological cycle of mountain watersheds having the largest biodiversity per unit area. In Venezuela, cloud forests are subject to intense deforestation and fragmentation by farming and cattle-ranching causing soil erosion, water cycle alteration, and biodiversity loss. Reforestation projects used exotic species as *Pines* and *Eucalyptus*, native species were rarely planted by lacking knowledge on species requirements and management. We report the performance of 25 native cloud forest species differing in shade-tolerance, planted in mixed assemblies on degraded areas. Tree survival and the individual tree variables: total height, root-collar diameter, tree-slenderness, and crown-ratio were evaluated at 1, 2, 4.5 and 7 years-old. Data was analyzed with a repeated measures analysis of variance mixed model considering species shadetolerance, light intensity at planting and age as explanatory factors. Survival was over 80%. Shade-intolerant species displayed faster height and root-collar diameter growth. Shade-tolerant species had larger crown ratios due to persistence of lower branches; whereas, shade-intolerant showed signs of crown recession at age 7. Slenderness values from age 4.5 were indicative of good trees stability and health across treatments. The positive results have motivated landowners to establish

**Keywords:** active restoration, reforestation, species selection, successional status,

Reforestation is the action planting trees for recovering lands that were originally covered by forests that were cleared due to land change use (e.g. agriculture) or by natural phenomena. Worldwide, most planted forests are monocultures with native or exotic species, but mixed planted forests are increasingly established [1]. Reforestation together with afforestation is a way to reduce the pressure on natural

Ecological restoration, on the other hand, looks for overcoming the barriers for the recovery of degraded landscapes, creating forests that meet the ecosystem functionality and structure of the former primary forest [2, 3]. In the context of

Native Species for Ecological

*Ana Quevedo-Rojas and Mauricio Jerez-Rico*

native species plantations in critical areas with our support.

forests and satisfy the demand of forest goods and services.

shade tolerance, facilitation, survival, tropical forests, silviculture

Venezuelan Andes

#### **Chapter 2**

*Silviculture*

[76] Instituto Forestal Latinoamericano

[82] Guariguata M, Evans K. Advancing tropical forestry curricula through nontimber Forest products. International Forestry Review. 2010;**12**(4):418-426. Available from: http://www.jstor.org/

[83] Sist P, Sablayrolles P, Barthelon S, Sousa-Ota L, Kibler JF, Ruschel A, et al. The contribution of multiple use forest management to small farmers' annual incomes in the eastern Amazon. Forests.

[84] Griscom BW, Goodman RC, Burivalova Z, Putz FE. Carbon and biodiversity impacts of intensive versus extensive tropical forestry. Conservation Letters. 2018;**11**(1):1-16

stable/24309824

2014;**5**(7):1508-1531

(IFLA). Evaluación del sistema silvicultural plantaciones en fajas de enriquecimiento (PFE) en las reservas forestales Imataca, San Pedro y Dorado Tumeremo, estado Bolívar. Mérida, Venezuela: Instituto Forestal

Latinoamericano; 2010

[77] Hardt Ferreira dos

fcomm.2019.00055

[79] Paniz-Mondolfi AE,

Rodríguez-Morales AJ. Venezuelan science in dire straits. Science. 2014;**346**(6209):559. Available from: http://science.sciencemag.org/ content/346/6209/559.abstract

[80] International Tropical Timber Organization - ITTO. Criteria and indicators for the sustainable management of tropical forests. ITTO Policy Development Series No. 21. [Internet]. 2016. pp. 1-84. Available from: https://www.itto.int/ direct/topics/topics\_pdf\_download/ topics\_id=4872&no=1&disp=inline

[81] Nepstad D, McGrath D, Stickler C, Alencar A, Azevedo A, Swette B, et al. Slowing Amazon deforestation through public policy and interventions in beef and soy supply chains. Science.

2014;**344**(6188):1118-1123

Santos VA, Modolo GS, Ferreira MJ. How do silvicultural treatments alter the microclimate in a Central Amazon secondary forest? A focus on light changes. Journal of Environmental Management. 2020;**254**(October 2019):109816. Available from: https:// www.sciencedirect.com/science/article/ pii/S0301479719315348?dgcid=author

[78] Kappel K, Holmen SJ. Why science communication, and does it work? A taxonomy of science communication aims and a survey of the empirical evidence. Frontiers in Communication. 2019;**4**:55. Available from: https:// www.frontiersin.org/article/10.3389/

**24**

## Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests of the Venezuelan Andes

*Ana Quevedo-Rojas and Mauricio Jerez-Rico*

#### **Abstract**

Tropical cloud forests play a fundamental role in the hydrological cycle of mountain watersheds having the largest biodiversity per unit area. In Venezuela, cloud forests are subject to intense deforestation and fragmentation by farming and cattle-ranching causing soil erosion, water cycle alteration, and biodiversity loss. Reforestation projects used exotic species as *Pines* and *Eucalyptus*, native species were rarely planted by lacking knowledge on species requirements and management. We report the performance of 25 native cloud forest species differing in shade-tolerance, planted in mixed assemblies on degraded areas. Tree survival and the individual tree variables: total height, root-collar diameter, tree-slenderness, and crown-ratio were evaluated at 1, 2, 4.5 and 7 years-old. Data was analyzed with a repeated measures analysis of variance mixed model considering species shadetolerance, light intensity at planting and age as explanatory factors. Survival was over 80%. Shade-intolerant species displayed faster height and root-collar diameter growth. Shade-tolerant species had larger crown ratios due to persistence of lower branches; whereas, shade-intolerant showed signs of crown recession at age 7. Slenderness values from age 4.5 were indicative of good trees stability and health across treatments. The positive results have motivated landowners to establish native species plantations in critical areas with our support.

**Keywords:** active restoration, reforestation, species selection, successional status, shade tolerance, facilitation, survival, tropical forests, silviculture

#### **1. Introduction**

Reforestation is the action planting trees for recovering lands that were originally covered by forests that were cleared due to land change use (e.g. agriculture) or by natural phenomena. Worldwide, most planted forests are monocultures with native or exotic species, but mixed planted forests are increasingly established [1]. Reforestation together with afforestation is a way to reduce the pressure on natural forests and satisfy the demand of forest goods and services.

Ecological restoration, on the other hand, looks for overcoming the barriers for the recovery of degraded landscapes, creating forests that meet the ecosystem functionality and structure of the former primary forest [2, 3]. In the context of

ecological restoration, reforestation fit within the category of "active restoration" in which, in addition to suppressing the causes of disturbances (passive restoration), strategies are implemented to accelerate recovery and, if possible influence the trajectory of the succession [4, 5]. Active restoration is important in places in which the natural regeneration is slow or hindered by biophysical factors [3].

Mixed plantations consist in establishing two or more species in a same stand. Species within the stand can be combined in many arrangements from alternate monospecific patches, to rows or intimate assemblages with various species. Species can differ in site requirements, successional stage (pioneer, late successional), architecture, growth habits, and uses. Also, trees within the mixture can be planted at different times to create uneven-aged stands. Mixed plantations are more accepted by communities, can have larger productivity and provide a wider array of goods and services [6]. From the ecological restoration point of view, mixed plantations with native species is a useful option for recovering the functionality and diversity of tropical forests. Petit and Montagnini [7] found that native species mixed plantations have favorable social and economic functions, because they provide a variety of timber and non-timber goods and services including soil recovery, carbon sequestration, and increase in biodiversity. Mixed plantations have been successful as a restoration option for creating a forest cover under certain conditions, where forests cannot regenerate by natural successional mechanisms as is the case in degraded pasturelands. However, the silviculture and management of mixed species with native tropical cloud forests species is complex, because lack of knowledge on growing these species, availability of plant, and difficult silvicultural management, particularly in intimate mixtures.

The Andean cloud forests are considered biodiversity "hotspots" and top the list of the most vulnerable ecosystems worldwide due to their small area and the high rates of deforestation by changes in land use from forest to agriculture and livestock that is accelerating the loss and degradation of these ecosystems. Cloud forests are characterized by a persistent cloudiness year around and occur in mountainous areas with abrupt topography. The complex combination of biotic and abiotic factors originate habitats with a high spatial and temporal heterogeneity leading to a high biodiversity [8].

Reforestation experiences in the cloud forest of Venezuela have been mostly carried out with exotic species (pine, cypresses, eucalyptus, ash, acacias) in monospecific cultures, and rarely in small tracts with several species. Native species plantation were included in past projects, but they were not successful due to failure to exclude main threats, lack of knowledge of site species requirements, improper planting methods, and absence of further care and monitoring in the initial stages. In general, seedlings of tree cloud forest species are characterized by slow growth and low tolerance to direct sunlight. In Venezuela, methods for production in nursery, plantation establishment, and management for these species are unknown. In 2007, our team began research projects aimed to study systematically cloud forest species requirements. Research included the distribution of seedlings of tree species in the forest understory along a light gradient [9, 10] and ecophysiological and morphological responses to contrasting light conditions [11, 12]. In 2012, we began a project aimed to develop and execute a plan for the landscape ecological restoration in the cloud forest of Paramo El Tambor with participation of stakeholders to restore degraded areas and help to protect the wildlife and their habitats. The plan includes several strategies of passive and active restoration. Among these, we initiated the establishment of small scale trials consisting of reforesting with native species in mixtures on deforested, degraded sites

The objective of this work was to report the performance of mixed species plantations, including more than 25 native species with different requirements of shade

**27**

**Figure 1.**

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests…*

shade-tolerance groups growing in sites with different levels of shade.

tolerance (shade-intolerant species; shade-tolerant species; partially shade species) established on degraded areas, originally covered by exotic pastures and some isolated trees. We describe the procedures for plant production, establishment, care and evaluated growth performance at ages 1, 2, 4.5, and 7 year-old for the different

The study was carried out in Paramo El Tambor, an isolated mountain massif part of the Venezuelan Andes (8°37′00″N; 71°21′00″W) facing the Maracaibo Lake with unique environmental characteristics (**Figure 1**). Politically is located in the

The tropical climate is influenced by altitude (2.000–3.000 m.a.s.l.) and topography. The trade winds coming from the NE penetrate through the piedmont area facing the lacustrine plain of Lake Maracaibo. These winds come loaded with water vapor forming a persistent cloudiness that when reaching its saturation point, triggers local precipitations in the slopes and valleys. The persistent thick cloudiness induces the existence of dense cloud forests from 2000 to 2500 m a.s.l. The annual average temperature is 14.9°C and average precipitation is 1400–1560 mm with a

The landscape consists of rounded hills, with shallow to steep slopes. The soils are derived from the Colón Cretaceous formation characterized by stratified, massive, black, non-calcareous lutites with conchoidal fractures. Predominant soils are Ultisols and Inceptisols with and Udic regime of clay-silty, clay-silty-loam to clayey

*Working Area Location of Páramo El Tambor, Mérida, Venezuela (Images: Google Earth, 2020).*

covered by dense cloud forests,

*DOI: http://dx.doi.org/10.5772/intechopen.95006*

Mérida state. The area occupies around 150 km2

*paramo* (moorlands), and wetlands.

short dry season (December–February).

**2. Materials and methods**

*2.1.1 Physical environment*

**2.1 Study area**

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests… DOI: http://dx.doi.org/10.5772/intechopen.95006*

tolerance (shade-intolerant species; shade-tolerant species; partially shade species) established on degraded areas, originally covered by exotic pastures and some isolated trees. We describe the procedures for plant production, establishment, care and evaluated growth performance at ages 1, 2, 4.5, and 7 year-old for the different shade-tolerance groups growing in sites with different levels of shade.

#### **2. Materials and methods**

#### **2.1 Study area**

*Silviculture*

ecological restoration, reforestation fit within the category of "active restoration" in which, in addition to suppressing the causes of disturbances (passive restoration), strategies are implemented to accelerate recovery and, if possible influence the trajectory of the succession [4, 5]. Active restoration is important in places in which

Mixed plantations consist in establishing two or more species in a same stand. Species within the stand can be combined in many arrangements from alternate monospecific patches, to rows or intimate assemblages with various species. Species can differ in site requirements, successional stage (pioneer, late successional), architecture, growth habits, and uses. Also, trees within the mixture can be planted at different times to create uneven-aged stands. Mixed plantations are more accepted by communities, can have larger productivity and provide a wider array of goods and services [6]. From the ecological restoration point of view, mixed plantations with native species is a useful option for recovering the functionality and diversity of tropical forests. Petit and Montagnini [7] found that native species mixed plantations have favorable social and economic functions, because they provide a variety of timber and non-timber goods and services including soil recovery, carbon sequestration, and increase in biodiversity. Mixed plantations have been successful as a restoration option for creating a forest cover under certain conditions, where forests cannot regenerate by natural successional mechanisms as is the case in degraded pasturelands. However, the silviculture and management of mixed species with native tropical cloud forests species is complex, because lack of knowledge on growing these species, availability of plant, and difficult silvicultural

The Andean cloud forests are considered biodiversity "hotspots" and top the list of the most vulnerable ecosystems worldwide due to their small area and the high rates of deforestation by changes in land use from forest to agriculture and livestock that is accelerating the loss and degradation of these ecosystems. Cloud forests are characterized by a persistent cloudiness year around and occur in mountainous areas with abrupt topography. The complex combination of biotic and abiotic factors originate habitats with a high spatial and temporal heterogeneity leading to a

Reforestation experiences in the cloud forest of Venezuela have been mostly carried out with exotic species (pine, cypresses, eucalyptus, ash, acacias) in monospecific cultures, and rarely in small tracts with several species. Native species plantation were included in past projects, but they were not successful due to failure to exclude main threats, lack of knowledge of site species requirements, improper planting methods, and absence of further care and monitoring in the initial stages. In general, seedlings of tree cloud forest species are characterized by slow growth and low tolerance to direct sunlight. In Venezuela, methods for production in nursery, plantation establishment, and management for these species are unknown. In 2007, our team began research projects aimed to study systematically cloud forest species requirements. Research included the distribution of seedlings of tree species in the forest understory along a light gradient [9, 10] and ecophysiological and morphological responses to contrasting light conditions [11, 12]. In 2012, we began a project aimed to develop and execute a plan for the landscape ecological restoration in the cloud forest of Paramo El Tambor with participation of stakeholders to restore degraded areas and help to protect the wildlife and their habitats. The plan includes several strategies of passive and active restoration. Among these, we initiated the establishment of small scale trials consisting of reforesting with native

The objective of this work was to report the performance of mixed species plantations, including more than 25 native species with different requirements of shade

the natural regeneration is slow or hindered by biophysical factors [3].

management, particularly in intimate mixtures.

species in mixtures on deforested, degraded sites

high biodiversity [8].

**26**

#### *2.1.1 Physical environment*

The study was carried out in Paramo El Tambor, an isolated mountain massif part of the Venezuelan Andes (8°37′00″N; 71°21′00″W) facing the Maracaibo Lake with unique environmental characteristics (**Figure 1**). Politically is located in the Mérida state. The area occupies around 150 km2 covered by dense cloud forests, *paramo* (moorlands), and wetlands.

The tropical climate is influenced by altitude (2.000–3.000 m.a.s.l.) and topography. The trade winds coming from the NE penetrate through the piedmont area facing the lacustrine plain of Lake Maracaibo. These winds come loaded with water vapor forming a persistent cloudiness that when reaching its saturation point, triggers local precipitations in the slopes and valleys. The persistent thick cloudiness induces the existence of dense cloud forests from 2000 to 2500 m a.s.l. The annual average temperature is 14.9°C and average precipitation is 1400–1560 mm with a short dry season (December–February).

The landscape consists of rounded hills, with shallow to steep slopes. The soils are derived from the Colón Cretaceous formation characterized by stratified, massive, black, non-calcareous lutites with conchoidal fractures. Predominant soils are Ultisols and Inceptisols with and Udic regime of clay-silty, clay-silty-loam to clayey

textures highly variable in depth, structural development, and drainage. Chemically, they are highly acid (pH 4–5) with a low base saturation, high exchangeable Al, low CEC and a high organic matter content (5.5 % C) in the upper horizon [13]. There are no large rivers coming from high moorlands, and horizontal precipitation captured by the forest plays and important role in the water balance [14].

#### *2.1.2 Vegetation*

The forests are rich in evergreen tree species densely covered by epiphytes, mosses, and lichens. Tree Diversity is high with 40-60 species ha−1 [15]. The main tree families are Lauraceae, Melastomataceae, Euphorbiaceae, Myrtaceae, and Podocarpaceae, constituting one of the few tropical forest in Venezuela where native conifers coexist with hardwoods. The forest comprises various plant communities ranging from dense high forest (DHF) with complex stratification and a canopy 25-30 m high to sparse low stature forests with canopies < 15 m tall. The DHF has three layers: the upper layer approximately 25-30 m in height with emergent trees up to 40 m tall (mainly *Retrophyllum rospigliosii*, a conifer), an intermediate layer 20-24 m in height, and a lower layer 10-19 m. The understory comprises tree seedlings and saplings, shrubs, vines, palms, and herbaceous plants. Tree ferns (*Cyathea spp*.) and bamboos (*Chusquea spp*.) are common, the latter forming dense scrubs [13].

#### *2.1.3 Socio-economic aspects*

The landscape is a mosaic in which traditional agricultural production methods and old agro-social structures coexist with intensive production systems, and legal figures of strict protection; whereas, land management with ecosystem approaches are less usual. The area have been subject to intense deforestation and forest fragmentation In recent times, local people are witnessing a rapid deterioration of their surrounding environment according to perception surveys carried as part of the community service project "Sensitization for the Conservation of the Andean Cloud Forest" (unpublished data). The areas in which deforestation was more intense are clearly suffering a reduction of water supply. In addition, they are more exposed to strong winds that damage the crops by mechanical and desiccation impacts. In recent times, the area is experiencing environmental changes such as longer dry seasons and extreme precipitation events. The later, together with exposed soils have caused landslides affecting roads and properties. Associated consequences of deforestation and degradation is the apparent extinction of some local wildlife species such as amphibians and monkeys.

#### **2.2 Species selection and plant production**

For selecting the species to produce in nursery, we took into account landowner's preferences and the findings of previous studies that analyzed the spatial distribution of seedlings of cloud forest tree species along a light gradient [8] and experiments in which seedlings of various species were grown under controlled levels of light intensity, then subjected to sudden changes in irradiation to observe their photosynthetic acclimation capacity [12]. According to these studies, we categorized the species in functional groups based on shade tolerance. Species fitted into three categories: (a) shade intolerant (SI), (b) partially shade tolerant (PT), and (c) shade tolerant (ST) (**Table 1**).

To produce plants, we collected seedlings from the forest understory because collecting viable seeds was very difficult, as many species have a very irregular cycle of flowering and seed production [19]. Seedlings were transplanted in polyethylene

**29**

*1*

*2*

**Table 1.**

*potential uses.*

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests…*

*Tetrorchidium rubrivenium* Euphorbiaceae SI WDF, FD, FA *Alchornea grandiflora* Euphorbiaceae SI WDF, MTB, FA *Montanoa quadrangularis* Asteraceae SI WDF, FD; FA *Ruagea pubescens* Meliaceae SI MTB; OR, FA *Cedrela montana* Meliaceae SI MTB, OR, FA *Inga oerstediana* Leguminosae SI MTB; FA, NF *Ocotea macropoda* Laureaceae SI MTB; FA *Miconia meridensis* Melastomataceae SI MTB, FA *Cecropia telenitida* Urticaceae SI MTB; OR *Hieronyma moritziana* Euphorbiaceae PT MTB, FA *Billia columbiana* Hippocastanaceae PT MD, MTB, FA *Casearia tachirensis* Flacourtiaceae PT HWR, MTB, FA *Beilschmiedia sulcata* Laureaceae PT HWR, FA *Nectadra laurel* Laureaceae PT MTB, FA *Prunus moritziana* Rosaceae PT MTB, OR, FA *Retrophyllum rospigliosii* Podocarpaceae PT MTB, OR, FA *Myrcia acuminata* Myrtaceae PT TB, FW, FA *Vochysia meridensis* Vochysiaceae PT MTB, OR, FA *Eugenia tamaensis* Myrtaceae ST MWR; FA

**Tolerance1**

**Uses2**

**Scientific name Family Shade** 

bags (diameter = 17 cm, height = 25 cm), in a mix 1:1 forest soil and sand. Plantlets were grown for at least six months in a nursery covered by an 80 % shade mesh

*Myrcianthes karsteniana* Myrtaceae ST HWR, OR, MD, FA

*Miconia resimoides* Melastomataceae ST MTB; OR *Podocarpus oleifolius* Podocarpaceae ST MTB, OR *Myrcia fallax* Myrtaceae ST MTB; MD *Aegiphila terniflora* Verbenaceae ST MTB, HWR, FA *Eschweilera tenax* Lecytidaceae ST HWR, FA

*Species uses: fodder (FD), fauna attraction (FA), medicinal (MD), firewood (FW), nitrogen fixing (NF), ornamental (OR), multipurpose timber (MTB), hardwood for building roofs (HWR), wooden fences (WDF).*

*List of species used for restoration in Paramo El Tambor cloud forest according to their shade tolerance and* 

*Species shade tolerance group: shade intolerant (SI), partially tolerant (PT), shade tolerant (ST).*

approximately 20% PPF of daily full sunlight [12]. Plants were irrigated regularly to avoid water stress. Weeds were removed manually and pest control was needed

**2.3 Site selection, plantation establishment, maintenance and monitoring**

Sites for planting were chosen together with stakeholders on deforested, degraded areas limiting with springs and having strong limitations for farming

s–1 of photosynthetic photon flux (PPF),

each, at 2250 to 2300 m a.s.l. Areas were

allowing the pass of 214–270 μmol m2

activities. The sites were 1200 to 1500 m2

against snails and slugs.

*DOI: http://dx.doi.org/10.5772/intechopen.95006*


*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests… DOI: http://dx.doi.org/10.5772/intechopen.95006*

*1 Species shade tolerance group: shade intolerant (SI), partially tolerant (PT), shade tolerant (ST). 2 Species uses: fodder (FD), fauna attraction (FA), medicinal (MD), firewood (FW), nitrogen fixing (NF), ornamental (OR), multipurpose timber (MTB), hardwood for building roofs (HWR), wooden fences (WDF).*

#### **Table 1.**

*Silviculture*

*2.1.2 Vegetation*

*2.1.3 Socio-economic aspects*

species such as amphibians and monkeys.

and (c) shade tolerant (ST) (**Table 1**).

**2.2 Species selection and plant production**

textures highly variable in depth, structural development, and drainage. Chemically, they are highly acid (pH 4–5) with a low base saturation, high exchangeable Al, low CEC and a high organic matter content (5.5 % C) in the upper horizon [13]. There are no large rivers coming from high moorlands, and horizontal precipitation

The forests are rich in evergreen tree species densely covered by epiphytes, mosses, and lichens. Tree Diversity is high with 40-60 species ha−1 [15]. The main tree families are Lauraceae, Melastomataceae, Euphorbiaceae, Myrtaceae, and Podocarpaceae, constituting one of the few tropical forest in Venezuela where native conifers coexist with hardwoods. The forest comprises various plant communities ranging from dense high forest (DHF) with complex stratification and a canopy 25-30 m high to sparse low stature forests with canopies < 15 m tall. The DHF has three layers: the upper layer approximately 25-30 m in height with emergent trees up to 40 m tall (mainly *Retrophyllum rospigliosii*, a conifer), an intermediate layer 20-24 m in height, and a lower layer 10-19 m. The understory comprises tree seedlings and saplings, shrubs, vines, palms, and herbaceous plants. Tree ferns (*Cyathea spp*.) and

bamboos (*Chusquea spp*.) are common, the latter forming dense scrubs [13].

The landscape is a mosaic in which traditional agricultural production methods and old agro-social structures coexist with intensive production systems, and legal figures of strict protection; whereas, land management with ecosystem approaches are less usual. The area have been subject to intense deforestation and forest fragmentation In recent times, local people are witnessing a rapid deterioration of their surrounding environment according to perception surveys carried as part of the community service project "Sensitization for the Conservation of the Andean Cloud Forest" (unpublished data). The areas in which deforestation was more intense are clearly suffering a reduction of water supply. In addition, they are more exposed to strong winds that damage the crops by mechanical and desiccation impacts. In recent times, the area is experiencing environmental changes such as longer dry seasons and extreme precipitation events. The later, together with exposed soils have caused landslides affecting roads and properties. Associated consequences of deforestation and degradation is the apparent extinction of some local wildlife

For selecting the species to produce in nursery, we took into account landowner's preferences and the findings of previous studies that analyzed the spatial distribution of seedlings of cloud forest tree species along a light gradient [8] and experiments in which seedlings of various species were grown under controlled levels of light intensity, then subjected to sudden changes in irradiation to observe their photosynthetic acclimation capacity [12]. According to these studies, we categorized the species in functional groups based on shade tolerance. Species fitted into three categories: (a) shade intolerant (SI), (b) partially shade tolerant (PT),

To produce plants, we collected seedlings from the forest understory because collecting viable seeds was very difficult, as many species have a very irregular cycle of flowering and seed production [19]. Seedlings were transplanted in polyethylene

captured by the forest plays and important role in the water balance [14].

**28**

*List of species used for restoration in Paramo El Tambor cloud forest according to their shade tolerance and potential uses.*

bags (diameter = 17 cm, height = 25 cm), in a mix 1:1 forest soil and sand. Plantlets were grown for at least six months in a nursery covered by an 80 % shade mesh allowing the pass of 214–270 μmol m2 s–1 of photosynthetic photon flux (PPF), approximately 20% PPF of daily full sunlight [12]. Plants were irrigated regularly to avoid water stress. Weeds were removed manually and pest control was needed against snails and slugs.

#### **2.3 Site selection, plantation establishment, maintenance and monitoring**

Sites for planting were chosen together with stakeholders on deforested, degraded areas limiting with springs and having strong limitations for farming activities. The sites were 1200 to 1500 m2 each, at 2250 to 2300 m a.s.l. Areas were covered by grasses, usually kikuyu grass (*Pennisetum clandestinum*), shrubs, vines (e.g., *Rubus fruticosus*) and isolated trees. Sites varied in slope (30-80%) with soils poor in organic matter and nutrients. Most sites were exposed to direct sunlight; however, tree crowns close or within the planting areas projected shade that reduced the incident light at ground level. In the chosen sites, we delimited the area and made a topographic survey. Pastures and vines were cut with a grass-cutting machine. Trees and shrubs from natural regeneration were left. The areas were delimited with wired fences to exclude cattle. In addition, we estimated the light environment in the sites by using as a surrogate the percentage of canopy openness (%CO) [8]. This variable provides a good characterization of the potential penetration of solar radiation through canopies and its incidence on a given point [16]. For estimating the %CO, we took hemispherical photographs on the vertices of a superposed 5.0 m square-grid covering the planting areas (n= 140). We used a digital camera with a fisheye lens mounted on a tripod and leveled with the top of the lens standing 150 cm above the ground. The photos were processed with Gap Light Analyzer (GLA) v. 2.0 [17]. For detailed procedures see [9, 18].

For site preparation no tillage was done, so the soil was disturbed only when opening the planting holes. Around the holes, grasses and other weeds were removed from root. Planting was done during the rainy season.

In all areas, plants were established following a horizontal (slope corrected) triangular spacing of 1.5 m (5.128 trees ha−1). A regular spacing was preferred over an irregular one for controlling variables of stand density and competition and easiness for monitoring. Also, landowners showed a marked preference for regular spacing. The selected planting density is very high for tropical plantations standards (600-2500 tree ha−1), but we looked to ensure survival of sufficient trees to reach faster shading for controlling pastures, and to observe competition/facilitation interactions as soon as possible.

Planting areas were subdivided in plots (~200 m<sup>2</sup> each, ~100 trees per plot). Plots were assigned to levels of light intensity (LI) based on %CO at planting time. Three levels of LI were differentiated: (a) High Light (HL, above 50% CO); (b) Medium Light-(ML, 40–50 % CO); and, Low Light intensity (LL <40 % CO).

In plantation rows, within each plot, two trees of the same species were planted consecutively forming a "group". Groups were alternated randomly, but with the restriction that at least two groups from each shade tolerance category should be included within plots classified within a given light intensity level (**Figure 2**). Planting two trees looked to improve the probabilities of at least one tree surviving, so maintaining a regular distribution within the plantation. The less promising tree will be eliminated when thinning is needed. The approximate planting ratio of SI, PT, and ST was 5:3:2, as ST species were more difficult to grow in nursery until reaching the desired size (20–40 cm tall). Mechanical-manual control of weeds was needed at least every six months until age 2. Cleanings consisted of eliminating vines and weeds rooted around the tree stem in a circle of 50 cm radius. Weeding was done prior to each measurement time to facilitate access to the trees. No chemicals were used for controlling pests or plagues that periodically affected some species. Irrigation, was needed only during the first dry season after planting. A replanting was done six months after planting to replace dead plants.

#### **2.4 Measurements and statistical design**

We sampled 12 plots (~200 m2 each, ~80–90 trees per plot) covering all combinations of light intensity (LI), species shade-tolerance (STOL), and ages. All plots included species of the three groups of shade tolerance; however, not all species were present in a given plot. The trials were re-measured at ages 1, 2, 4.5 and 7 years. Percent

**31**

**Figure 2.**

highly significant differences.

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests…*

tree survival was determined for each combination of light intensity and shade tolerance group as the percentage of surviving trees at a given age with respect to the initial number of planted trees. For each tree, we measured (a) total height in meters (HT), (b) root collar diameter in cm (RCD) and computed (a) tree slenderness coefficient (TSC) calculated as total height (m) divided by root collar diameter (m), and (b) crown ratio (CR) calculated as live crown length (m) divided by total height (m). The TSC is an important indicator of tree stability. In general, a tree with a low TSC usually indicates lower center of gravity with a longer crown length, and a better developed root system increasing resistance to falling by strong winds and other factors [19–21]. The CR varies between 0 and 1, with a large live crown ratio indicating a healthy tree able to respond to favorable changes such as canopy openings [22]. To analyze the data, a factorial analysis of variance (ANOVA) mixed model

*Spatial arrangement of groups of plants within a plot. Spacing is triangular (1.5 m) and distance between rows is 1.3 m. Legend: hemispherical photographs ( ) taken on the vertices of the white grid, planted rows* 

*( ), fences ( ), shade intolerant ( ), partially tolerant ( ), and shade tolerant plants ( ).*

was used in which STOL and LI factors were considered as fixed effects.

Re-measurement age was considered a repeated effect, as the same plants and plots were re-measured at the various ages. Only the largest tree in each group of two of a same species was chosen for data analysis, as it was assumed that this expressed best the growth potential under the site conditions predominating in the plot. The second tree, if survived, usually grew less due to slow initial growth, or mechanical damage. Also, damaged trees were discarded from analysis (e.g., broken trees).

Data were stored in a spreadsheet and processed in SAS v. 9.1 [23]. For each variable, several models with varying structure of the variance-covariance matrix were tested. The best model was that with the lower value of the Akaike and Bayesian information criteria (AIC and BIC) [24]. For each variable, simple effects (shade tolerance, light intensity, and age) and resulting interactions within and across age were analyzed for shade tolerance and light intensity. The model takes into account the correlation between repeated measurements normality and variance heterogeneity along time [25]. As the design is unbalanced, a Tukey-Kramer test based on marginal means (least squares means) [26] allowed comparisons for differences among shade-tolerance groups and light intensity at similar re-measurement times. Probability values (p-values) indicated the statistical significance of effects and interactions. For simplicity in means comparisons, p-values ≥ 0.05 indicated no significant differences, p-value < 0.05, significant differences, and p-value < 0.01,

*DOI: http://dx.doi.org/10.5772/intechopen.95006*

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests… DOI: http://dx.doi.org/10.5772/intechopen.95006*

#### **Figure 2.**

*Silviculture*

covered by grasses, usually kikuyu grass (*Pennisetum clandestinum*), shrubs, vines (e.g., *Rubus fruticosus*) and isolated trees. Sites varied in slope (30-80%) with soils poor in organic matter and nutrients. Most sites were exposed to direct sunlight; however, tree crowns close or within the planting areas projected shade that reduced the incident light at ground level. In the chosen sites, we delimited the area and made a topographic survey. Pastures and vines were cut with a grass-cutting machine. Trees and shrubs from natural regeneration were left. The areas were delimited with wired fences to exclude cattle. In addition, we estimated the light environment in the sites by using as a surrogate the percentage of canopy openness (%CO) [8]. This variable provides a good characterization of the potential penetration of solar radiation through canopies and its incidence on a given point [16]. For estimating the %CO, we took hemispherical photographs on the vertices of a superposed 5.0 m square-grid covering the planting areas (n= 140). We used a digital camera with a fisheye lens mounted on a tripod and leveled with the top of the lens standing 150 cm above the ground. The photos were processed with Gap

Light Analyzer (GLA) v. 2.0 [17]. For detailed procedures see [9, 18].

removed from root. Planting was done during the rainy season.

Planting areas were subdivided in plots (~200 m<sup>2</sup>

interactions as soon as possible.

For site preparation no tillage was done, so the soil was disturbed only when opening the planting holes. Around the holes, grasses and other weeds were

In all areas, plants were established following a horizontal (slope corrected) triangular spacing of 1.5 m (5.128 trees ha−1). A regular spacing was preferred over an irregular one for controlling variables of stand density and competition and easiness for monitoring. Also, landowners showed a marked preference for regular spacing. The selected planting density is very high for tropical plantations standards (600-2500 tree ha−1), but we looked to ensure survival of sufficient trees to reach faster shading for controlling pastures, and to observe competition/facilitation

Plots were assigned to levels of light intensity (LI) based on %CO at planting time. Three levels of LI were differentiated: (a) High Light (HL, above 50% CO); (b) Medium Light-(ML, 40–50 % CO); and, Low Light intensity (LL <40 % CO).

In plantation rows, within each plot, two trees of the same species were planted consecutively forming a "group". Groups were alternated randomly, but with the restriction that at least two groups from each shade tolerance category should be included within plots classified within a given light intensity level (**Figure 2**). Planting two trees looked to improve the probabilities of at least one tree surviving, so maintaining a regular distribution within the plantation. The less promising tree will be eliminated when thinning is needed. The approximate planting ratio of SI, PT, and ST was 5:3:2, as ST species were more difficult to grow in nursery until reaching the desired size (20–40 cm tall). Mechanical-manual control of weeds was needed at least every six months until age 2. Cleanings consisted of eliminating vines and weeds rooted around the tree stem in a circle of 50 cm radius. Weeding was done prior to each measurement time to facilitate access to the trees. No

chemicals were used for controlling pests or plagues that periodically affected some species. Irrigation, was needed only during the first dry season after planting. A

nations of light intensity (LI), species shade-tolerance (STOL), and ages. All plots included species of the three groups of shade tolerance; however, not all species were present in a given plot. The trials were re-measured at ages 1, 2, 4.5 and 7 years. Percent

each, ~80–90 trees per plot) covering all combi-

replanting was done six months after planting to replace dead plants.

**2.4 Measurements and statistical design**

We sampled 12 plots (~200 m2

each, ~100 trees per plot).

**30**

*Spatial arrangement of groups of plants within a plot. Spacing is triangular (1.5 m) and distance between rows is 1.3 m. Legend: hemispherical photographs ( ) taken on the vertices of the white grid, planted rows ( ), fences ( ), shade intolerant ( ), partially tolerant ( ), and shade tolerant plants ( ).*

tree survival was determined for each combination of light intensity and shade tolerance group as the percentage of surviving trees at a given age with respect to the initial number of planted trees. For each tree, we measured (a) total height in meters (HT), (b) root collar diameter in cm (RCD) and computed (a) tree slenderness coefficient (TSC) calculated as total height (m) divided by root collar diameter (m), and (b) crown ratio (CR) calculated as live crown length (m) divided by total height (m).

The TSC is an important indicator of tree stability. In general, a tree with a low TSC usually indicates lower center of gravity with a longer crown length, and a better developed root system increasing resistance to falling by strong winds and other factors [19–21]. The CR varies between 0 and 1, with a large live crown ratio indicating a healthy tree able to respond to favorable changes such as canopy openings [22].

To analyze the data, a factorial analysis of variance (ANOVA) mixed model was used in which STOL and LI factors were considered as fixed effects. Re-measurement age was considered a repeated effect, as the same plants and plots were re-measured at the various ages. Only the largest tree in each group of two of a same species was chosen for data analysis, as it was assumed that this expressed best the growth potential under the site conditions predominating in the plot. The second tree, if survived, usually grew less due to slow initial growth, or mechanical damage. Also, damaged trees were discarded from analysis (e.g., broken trees).

Data were stored in a spreadsheet and processed in SAS v. 9.1 [23]. For each variable, several models with varying structure of the variance-covariance matrix were tested. The best model was that with the lower value of the Akaike and Bayesian information criteria (AIC and BIC) [24]. For each variable, simple effects (shade tolerance, light intensity, and age) and resulting interactions within and across age were analyzed for shade tolerance and light intensity. The model takes into account the correlation between repeated measurements normality and variance heterogeneity along time [25]. As the design is unbalanced, a Tukey-Kramer test based on marginal means (least squares means) [26] allowed comparisons for differences among shade-tolerance groups and light intensity at similar re-measurement times. Probability values (p-values) indicated the statistical significance of effects and interactions. For simplicity in means comparisons, p-values ≥ 0.05 indicated no significant differences, p-value < 0.05, significant differences, and p-value < 0.01, highly significant differences.

### **3. Results and discussion**

#### **3.1 Survival**

Survival was high for all categories of shade tolerance within different levels of light intensity averaging over 70% for all plots after year 4.5 (**Table 2**). Only one plot was discarded from analysis because flooding caused high mortality (>50%). In the remaining plots, the SI species had a survival above 85% after 4.5 years with a slightly better survival in LL. Also, PT species showed better survival in LL (above 90%), but only 73–77% in HL and ML. Shade Tolerant species presented the lower values of survival in HL; nonetheless, values remained above 70 % after year 4.5. In ML this group maintained over 80 % survival, and above 90% in LL. Only two species *M. resimoides* and *E. tenax* (n > 10 each) had 100% mortality before the second year. After age 2, most mortality was due to mechanical damage by the fall of large branches from the isolated trees and occasional herbivory and cramping by cattle that passed the fences. There are very few studies for mixed plantations in tropical cloud forests that report survival results of native species after four years-old.

In a Mexican cloud forest [27] evaluated mixed plantation trials with up to nine native species and found an average survival of 93% three years after planting. They concluded that if plants survive the establishment phase, mortality in further years is low. In the same study, the authors reported that in a trial with the native species *Alnus acuminata* and *Quercus xalapensis* growing on native and exotic abandoned grass, the combined survival was 92 and 48 % after 46 weeks since planting. Higher mortality on exotic grass varied between species due to competition and herbivory from rats. Also in a Mexican cloud forest [28] planted *Alnus acuminata* and *Trema micrantha* as facilitating species for the establishment of intermediate and late successional species (ILS). At age 2 (96 weeks), survival was 94 and 77% respectively for the facilitating species. On the other hand, the survival of the three ILS was significantly higher (>60%) under the shade of *A. acuminata*, and 40–50% under *T. micrantha*. When planted on open field survival was only 11 to 22% for the ILS. They attributed the low survival in the open field to water stress accompanied with herbivory. In the Atlantic semi-deciduous forest of Brazil, [29] compared the


*2 Light intensity: high light (HL), medium light (ML), low light (LL).*

#### **Table 2.**

*Percent survival ± standard deviation (n = 11 plots) for combinations of shade tolerance and light intensity at the ages of measurement.*

**33**

*1*

*2*

**Table 3.**

*highly significant differences.*

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests…*

survival of 36 native species from different successional stages established as mixed plantations on degraded sites. Before planting they plowed and fertilized the sites. Fifteen after planting survival was around 55% for pioneer and secondary species, and only 12% for the late successional ones. The high survival rates for most species in the present report was due to a relatively intense monitoring and maintenance within the first two years after planting. The main silvicultural treatments included avoiding water stress with irrigation in the first dry season after planting and controlling aggressive weeds and grass at least for two years. Keeping cattle exclusion was also critical. Although insects and pests attacked particular species at different times, they rarely caused mortality. Finally, in areas shaded by mature trees, the fall of large branches caused mechanical damage to some trees which eventually died.

For all variables measured on individual trees, a mixed model with an autoregressive first-order residual variance-covariance matrix performed best than alternative structures (lowest AIC and BIC criteria). The type III test for fixed effects showed highly significant differences for simple effects, except for CR with p > 0.05 (**Table 3**). The interaction STOL × AGE was significant for all variables; whereas, LI × AGE was significant (p < 0.05) for TH, and highly significant for the rest of variables. The interaction STOL × LI was also significant for all variables except for TSC (p >0.05). The interaction STOL×LI×AGE was not significant. The LI factor is based on values of %CO at the beginning of the plantations, and although changes in light incidence above the canopy (isolated trees) were minimum, the largest planted trees of SI species began to reduce the amount of light received by smaller trees included most of the ST. Mixtures of shade intolerant, early successional species and shade-tolerant, late-successional species, could facilitate the survival and

These results indicate that trees from the three STOL groups underwent significant changes in the evaluated variables along age and across plots differing in initial

**Variable1 STOL LI AGE STOL x AGE LI x AGE STOL x LI** TH (m) <.0001 0.0001 <.0001 <.0001 0.0152 0.0005 RCD (cm) <.0001 <.0006 <.0001 <.0001 <.0001 0.0200 TSC 0.0015 <.0001 <.0001 <.0001 <.0001 *0.0917* CR <.0001 *0.4635* <.0001 <.0004 0.0083 0.0168

*Variables: total height (TH), root collar diameter (RCD), tree slenderness coefficient (TSC), crown ratio (CR).*

*Simple effects and interactions for the analyzed variables. Triple interaction not included. Means comparisons p-values* ≥ *0.05 indicated no significant differences, p-value < 0.05, significant differences, and p-value < 0.01,* 

*Factors and interactions: shade tolerance (STOL), light intensity (LI).*

The most insightful results were for the STOL x AGE interactions where the averaged values of variables for each STOL group were compared within and along ages (**Figure 3a,b**). The STOL groups did not differ significantly in TH the first year after planting; but, after age two, the SI group presented significantly larger heights than the PT-ST groups (**Figure 3a**). Differences in TH among the three groups become larger at ages 4.5 and 7 years, with SI species growing faster than PT, and the ST species showing the lower height growth. Despite differences in total height the three groups appear to be growing at an increased rate with age. After 7 years

LI levels, with the SI species showing faster growth at all levels of LI.

*DOI: http://dx.doi.org/10.5772/intechopen.95006*

**3.2 Tree level variables**

growth of the latter [30].

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests… DOI: http://dx.doi.org/10.5772/intechopen.95006*

survival of 36 native species from different successional stages established as mixed plantations on degraded sites. Before planting they plowed and fertilized the sites. Fifteen after planting survival was around 55% for pioneer and secondary species, and only 12% for the late successional ones. The high survival rates for most species in the present report was due to a relatively intense monitoring and maintenance within the first two years after planting. The main silvicultural treatments included avoiding water stress with irrigation in the first dry season after planting and controlling aggressive weeds and grass at least for two years. Keeping cattle exclusion was also critical. Although insects and pests attacked particular species at different times, they rarely caused mortality. Finally, in areas shaded by mature trees, the fall of large branches caused mechanical damage to some trees which eventually died.

#### **3.2 Tree level variables**

*Silviculture*

**3.1 Survival**

**3. Results and discussion**

Survival was high for all categories of shade tolerance within different levels of light intensity averaging over 70% for all plots after year 4.5 (**Table 2**). Only one plot was discarded from analysis because flooding caused high mortality (>50%). In the remaining plots, the SI species had a survival above 85% after 4.5 years with a slightly better survival in LL. Also, PT species showed better survival in LL (above 90%), but only 73–77% in HL and ML. Shade Tolerant species presented the lower values of survival in HL; nonetheless, values remained above 70 % after year 4.5. In ML this group maintained over 80 % survival, and above 90% in LL. Only two species *M. resimoides* and *E. tenax* (n > 10 each) had 100% mortality before the second year. After age 2, most mortality was due to mechanical damage by the fall of large branches from the isolated trees and occasional herbivory and cramping by cattle that passed the fences. There are very few studies for mixed plantations in tropical cloud forests that report survival results of native species after four years-old.

In a Mexican cloud forest [27] evaluated mixed plantation trials with up to nine native species and found an average survival of 93% three years after planting. They concluded that if plants survive the establishment phase, mortality in further years is low. In the same study, the authors reported that in a trial with the native species *Alnus acuminata* and *Quercus xalapensis* growing on native and exotic abandoned grass, the combined survival was 92 and 48 % after 46 weeks since planting. Higher mortality on exotic grass varied between species due to competition and herbivory from rats. Also in a Mexican cloud forest [28] planted *Alnus acuminata* and *Trema micrantha* as facilitating species for the establishment of intermediate and late successional species (ILS). At age 2 (96 weeks), survival was 94 and 77% respectively for the facilitating species. On the other hand, the survival of the three ILS was significantly higher (>60%) under the shade of *A. acuminata*, and 40–50% under *T. micrantha*. When planted on open field survival was only 11 to 22% for the ILS. They attributed the low survival in the open field to water stress accompanied with herbivory. In the Atlantic semi-deciduous forest of Brazil, [29] compared the

IS HL 121 92.1 ± 7 91.0 ± 9 88.4 ± 9 79.2 ± 10

PT HL 82 84.3 ± 10 81.6 ± 6 73.6 ± 14 64.9 ± 18

ST HL 51 76.0 ± 9 76.0 ± 9 73.5 ± 5 70.0 ± 5

*Percent survival ± standard deviation (n = 11 plots) for combinations of shade tolerance and light intensity at* 

*Species shade tolerance group: shade intolerant (SI), partially tolerant (PT), shade tolerant (ST).*

*Light intensity: high light (HL), medium light (ML), low light (LL).*

ML 223 95.9 ± 4 93.9 ± 6 89.4 ± 8 90.0 ± 5 LL 132 100.0 ± 0 100.0 ± 0 97.8 ± 3 91.3 ± 4

ML 120 91.2 ± 9 86.8 ± 12 76.9 ± 11 78.7 ± 4 LL 55 98.6 ± 2 97.1 ± 4 94.6 ± 1 94.3 ± 2

ML 101 98.5 ± 3 91.2 ± 8 82.9 ± 4 80.2 ± 8 LL 55 97.5 ± 4 96.1 ± 2 94.6 ± 1 91.4 ± 1

**Age (years) 1.0 2.0 4.5 7.0**

**32**

*1*

*2*

**Table 2.**

*the ages of measurement.*

**Shade tolerance**

**Light intensity**

**Trees planted**

For all variables measured on individual trees, a mixed model with an autoregressive first-order residual variance-covariance matrix performed best than alternative structures (lowest AIC and BIC criteria). The type III test for fixed effects showed highly significant differences for simple effects, except for CR with p > 0.05 (**Table 3**). The interaction STOL × AGE was significant for all variables; whereas, LI × AGE was significant (p < 0.05) for TH, and highly significant for the rest of variables. The interaction STOL × LI was also significant for all variables except for TSC (p >0.05). The interaction STOL×LI×AGE was not significant. The LI factor is based on values of %CO at the beginning of the plantations, and although changes in light incidence above the canopy (isolated trees) were minimum, the largest planted trees of SI species began to reduce the amount of light received by smaller trees included most of the ST. Mixtures of shade intolerant, early successional species and shade-tolerant, late-successional species, could facilitate the survival and growth of the latter [30].

These results indicate that trees from the three STOL groups underwent significant changes in the evaluated variables along age and across plots differing in initial LI levels, with the SI species showing faster growth at all levels of LI.

The most insightful results were for the STOL x AGE interactions where the averaged values of variables for each STOL group were compared within and along ages (**Figure 3a,b**). The STOL groups did not differ significantly in TH the first year after planting; but, after age two, the SI group presented significantly larger heights than the PT-ST groups (**Figure 3a**). Differences in TH among the three groups become larger at ages 4.5 and 7 years, with SI species growing faster than PT, and the ST species showing the lower height growth. Despite differences in total height the three groups appear to be growing at an increased rate with age. After 7 years


*2 Factors and interactions: shade tolerance (STOL), light intensity (LI).*

#### **Table 3.**

*Simple effects and interactions for the analyzed variables. Triple interaction not included. Means comparisons p-values* ≥ *0.05 indicated no significant differences, p-value < 0.05, significant differences, and p-value < 0.01, highly significant differences.*

**Figure 3.**

*Changes in total height and root collar diameter among shade tolerance species groups with age. (a) Total height, (b) root collar diameter. 1 Species shade tolerance group: shade intolerant (SI), partially tolerant (PT), shade tolerant (ST). <sup>2</sup> Similar letters below the lines indicate statistically not significant differences (p>0.05) among shade tolerance groups; whereas, different letters indicate significant differences (p < 0.05) according to the Tukey-Kramer test.*

average height increments can be considered low (< 1 m yr−1) when compared with the growth increments for lowland tropical species (2–4 m yr−1) and the growth of exotic species such as cypresses and pines. However, SI species had many trees close to 10 m tall at age 7. These trees also developed large, wide crowns (e.g., *M. quadrangularis, T. rubrivenium, M. meridensis*). Likewise, for RCD there were no differences among STOL groups for ages 1–2; whereas at ages 4.5 and 7, in which the three groups, with SI having a larger RCD than the other groups (**Figure 3b**).

When considering the STOL × LI interaction effect on the performance of TH and RCD, the Tukey test indicated no statistically significant differences (p > 0.05) at ages 1 and 2 years among the STOL groups, independently of LI for any of these variables. However, at ages 4.5 and 7, SI species showed significantly better performance in both variables than PT-ST species. Likewise, no significant differences were found for HT and RCD between PT and ST species across LI levels.

The TSC had not significant differences among groups at age 1 (**Figure 4a**). At age 2, all species increased their TSC (above 1.0), with a significantly higher increment for the ST-PT species over the SI species. Possibly, TSC at age 1 reflected the values that trees had in the nursery. Larger TSC for the second year could be due to a faster growth in height relative to RCD growth, indicating a faster stem elongation and formation of leaves at the top of the trees. By ages 4.5 and 7, TSC decreased again and stabilized for all groups, with no significant differences among them. The lower TSC indicates that the trees have more stability and are showing an adequate growth pattern [20].

Finally, the live crown ratio (**Figure 4b**) was significantly higher (>0.6) for the ST group than for PT-SI. By age 4.5 however, there was a considerable increase in CR for the PT and SI groups with no significant differences among STOL groups. Nonetheless, SI species had the lowest CR. At age 7, CR was similar (above 0.7) for

**35**

**Figure 4.**

*Tree slenderness coefficient, (b) crown ratio. 1*

*(p < 0.05) according to the Tukey-Kramer test.*

*Tolerant (PT), Shade Tolerant (ST). <sup>2</sup>*

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests…*

ST and PT and clearly higher than for SI species (0.6). The large CR for ST species is explained by the trend to have persistent leaves and branches along most of the stem along the years. This finding is supported by [31] who working with the plasticity traits of saplings from the tropic humid forest in the French Guiana determined that crown depth in shade tolerant species was a trait that depended on the leaf lifespan rather than crown elongation. In PT, and specially SI, the rapid height growth was accompanied by a large development in crown length; however by age 7, SI trees displayed signs of crown recession, as shaded leaves on the lower branches were dying quickly. Conversely to shade tolerant trees, [31] shorter crowns in SI species was attributed to a shorter lifespan of leaves. Usually, trees showing CR above 0.5 can be considered healthy; whereas, values below 0.3 indicate trees that are under strong competition. In addition, a characteristic shade intolerant species is the trend to reduce faster their CR under competition, because lower limbs tend

*Changes in tree slenderness coefficient and crown ratio among shade tolerance species groups with age. (a)* 

*differences (p>0.05) among shade tolerance groups; whereas, different letters indicate significant differences* 

*Species shade tolerance group: Shade Intolerant (SI), Partially* 

*Similar letters below the lines indicate statistically not significant* 

to die due to insufficient light for having a net positive C assimilation.

within light levels for any of the STOL groups.

At age 1, the TSC coefficient was significantly larger at ML for the three STOL groups than at HL or LL; differences were significantly higher slenderness in ML than in HL or LL; whereas, PT and ST species. At age 2, TSC remained stable for all STOL groups in the ML level, but the values increased significantly for all groups in HL and LL. At ages 4.5 and 7 no differences in TSC were found for any of the STOL groups in any LI level. Finally, at age 1 and 2, CR had significantly larger values in ML than in HL or LL. For ages, 4.5 and 7, there were no significant differences

The relatively low effect of LI levels on the performance of SI species support findings by [32] who suggest these species had an inherent fast growth rate

*DOI: http://dx.doi.org/10.5772/intechopen.95006*

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests… DOI: http://dx.doi.org/10.5772/intechopen.95006*

**Figure 4.**

*Silviculture*

**Figure 3.**

*height, (b) root collar diameter. 1*

*shade tolerant (ST). <sup>2</sup>*

*the Tukey-Kramer test.*

average height increments can be considered low (< 1 m yr−1) when compared with the growth increments for lowland tropical species (2–4 m yr−1) and the growth of exotic species such as cypresses and pines. However, SI species had many trees close to 10 m tall at age 7. These trees also developed large, wide crowns (e.g., *M. quadrangularis, T. rubrivenium, M. meridensis*). Likewise, for RCD there were no differences among STOL groups for ages 1–2; whereas at ages 4.5 and 7, in which the three groups, with SI having a larger RCD than the other groups (**Figure 3b**).

*among shade tolerance groups; whereas, different letters indicate significant differences (p < 0.05) according to* 

*Changes in total height and root collar diameter among shade tolerance species groups with age. (a) Total* 

*Species shade tolerance group: shade intolerant (SI), partially tolerant (PT),* 

*Similar letters below the lines indicate statistically not significant differences (p>0.05)* 

When considering the STOL × LI interaction effect on the performance of TH and RCD, the Tukey test indicated no statistically significant differences (p > 0.05) at ages 1 and 2 years among the STOL groups, independently of LI for any of these variables. However, at ages 4.5 and 7, SI species showed significantly better performance in both variables than PT-ST species. Likewise, no significant differences

The TSC had not significant differences among groups at age 1 (**Figure 4a**). At age 2, all species increased their TSC (above 1.0), with a significantly higher increment for the ST-PT species over the SI species. Possibly, TSC at age 1 reflected the values that trees had in the nursery. Larger TSC for the second year could be due to a faster growth in height relative to RCD growth, indicating a faster stem elongation and formation of leaves at the top of the trees. By ages 4.5 and 7, TSC decreased again and stabilized for all groups, with no significant differences among them. The lower TSC indicates that the trees have more stability and are showing an adequate growth pattern [20].

Finally, the live crown ratio (**Figure 4b**) was significantly higher (>0.6) for the ST group than for PT-SI. By age 4.5 however, there was a considerable increase in CR for the PT and SI groups with no significant differences among STOL groups. Nonetheless, SI species had the lowest CR. At age 7, CR was similar (above 0.7) for

were found for HT and RCD between PT and ST species across LI levels.

**34**

*Changes in tree slenderness coefficient and crown ratio among shade tolerance species groups with age. (a) Tree slenderness coefficient, (b) crown ratio. 1 Species shade tolerance group: Shade Intolerant (SI), Partially Tolerant (PT), Shade Tolerant (ST). <sup>2</sup> Similar letters below the lines indicate statistically not significant differences (p>0.05) among shade tolerance groups; whereas, different letters indicate significant differences (p < 0.05) according to the Tukey-Kramer test.*

ST and PT and clearly higher than for SI species (0.6). The large CR for ST species is explained by the trend to have persistent leaves and branches along most of the stem along the years. This finding is supported by [31] who working with the plasticity traits of saplings from the tropic humid forest in the French Guiana determined that crown depth in shade tolerant species was a trait that depended on the leaf lifespan rather than crown elongation. In PT, and specially SI, the rapid height growth was accompanied by a large development in crown length; however by age 7, SI trees displayed signs of crown recession, as shaded leaves on the lower branches were dying quickly. Conversely to shade tolerant trees, [31] shorter crowns in SI species was attributed to a shorter lifespan of leaves. Usually, trees showing CR above 0.5 can be considered healthy; whereas, values below 0.3 indicate trees that are under strong competition. In addition, a characteristic shade intolerant species is the trend to reduce faster their CR under competition, because lower limbs tend to die due to insufficient light for having a net positive C assimilation.

At age 1, the TSC coefficient was significantly larger at ML for the three STOL groups than at HL or LL; differences were significantly higher slenderness in ML than in HL or LL; whereas, PT and ST species. At age 2, TSC remained stable for all STOL groups in the ML level, but the values increased significantly for all groups in HL and LL. At ages 4.5 and 7 no differences in TSC were found for any of the STOL groups in any LI level. Finally, at age 1 and 2, CR had significantly larger values in ML than in HL or LL. For ages, 4.5 and 7, there were no significant differences within light levels for any of the STOL groups.

The relatively low effect of LI levels on the performance of SI species support findings by [32] who suggest these species had an inherent fast growth rate determined mainly by morphological traits, but these growth rates are maintained at the expense of defense and storage allocation. As we could observe, SI species suffered from selective herbivory by cattle (i.e., leaves of trees from SI species were eaten; whereas those of PT-ST were not). On the other hand, as mentioned by the same author, survival of SI species cannot be attributed to a high net C balance

By age 7, the crown of SI species were in contact and forming an upper layer of dominant trees; whereas, PT and ST species conformed an intermediate layer. Although competition for light was not evident from the observed crown ratio values; the SI trees showed a large loss of leaves on their lower branches; whereas these persisted in trees of PT and ST, keeping large crown ratios despite being shaded. Only, between ages 5 and 7, the shade created by the new plantation has eradicated pastures, except in sites canopy holes created by tree mortality or in the borders of the planted sites. Natural regeneration of some tree and shrub species began after year two, and when taken into account increase stand density above 100%. In highly shaded areas, the presence of herbaceous plants is rather scarce and a fine layer of litter is forming.

#### **4. Conclusions**

Our research with tree native species and establishment of demonstrative trials in cloud forests show promising that reforesting with native species is a viable alternative for restoring degraded areas and the recovery of tree biodiversity given adequate planning, management and monitoring (**Figure 5**).

The most critical aspects for the initial success of these plantations consists on maintaining cattle exclusion for at least five years after establishment, irrigating during the first dry season, and keeping control of grasses and vines at least for two years.

Different mixed shade tolerance groups of tree species can stand conditions of sites dominated by pastures under high level of sunlight exposure; however, SI species appear to have faster growth rates than PT or ST species independently of shade conditions.

#### **Figure 5.**

*State of development of one of the mixed plantations: (a) one year old, (b) 2 years old, (c) 4.5 years old, (d) 7 years old.*

**37**

**Author details**

Venezuela

Ana Quevedo-Rojas\* and Mauricio Jerez-Rico

provided the original work is properly cited.

\*Address all correspondence to: anamer2@gmail.com

Facultad de Ciencias Forestales y Ambientales, University of Los Andes, Mérida,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests…*

Planting mixed forests is a good option for recovering degraded sites in which the forest has disappeared and conditions for unassisted tree regeneration is not possible. More than scaling up to cover larger extensions, many landowners can establish small plantations in critical areas. Many of these plantations can act as small nucleus for maintaining and dispersing rare, shade-tolerant, late successional species that usually are difficult to regenerate without specific silvicultural treatments.

Mixed planted forests have a very positive response from local people who view these plantations as a very satisfying way of recover the forests as pointed by [33] in

Among other benefits mixed planted forests with native species, provide food and shelter for wildlife, have better social acceptance because they are part of the natural landscape, and provide a variety of goods and services (e.g., shade, soil

Mixed plantations are complementary with other methods such as those of assisted

regeneration in degraded forests or passive restoration used to recover large areas.

We are grateful to Ancelmo Dugarte and Dani Dugarte for their invaluable assistance in fieldwork. This work was partially funded by Consejo de Desarrollo Científico, Humanístico, Tecnológico y de las Artes, University of Los Andes

*DOI: http://dx.doi.org/10.5772/intechopen.95006*

protection, medicinal properties).

(CDCHTA-ULA) (Grant F0–746–17–01-A).

The authors declare no conflict of interest.

**Acknowledgements**

**Conflict of interest**

a similar work in the Andean cloud forest of Ecuador.

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests… DOI: http://dx.doi.org/10.5772/intechopen.95006*

Planting mixed forests is a good option for recovering degraded sites in which the forest has disappeared and conditions for unassisted tree regeneration is not possible. More than scaling up to cover larger extensions, many landowners can establish small plantations in critical areas. Many of these plantations can act as small nucleus for maintaining and dispersing rare, shade-tolerant, late successional species that usually are difficult to regenerate without specific silvicultural treatments.

Mixed planted forests have a very positive response from local people who view these plantations as a very satisfying way of recover the forests as pointed by [33] in a similar work in the Andean cloud forest of Ecuador.

Among other benefits mixed planted forests with native species, provide food and shelter for wildlife, have better social acceptance because they are part of the natural landscape, and provide a variety of goods and services (e.g., shade, soil protection, medicinal properties).

Mixed plantations are complementary with other methods such as those of assisted regeneration in degraded forests or passive restoration used to recover large areas.

#### **Acknowledgements**

*Silviculture*

litter is forming.

**4. Conclusions**

shade conditions.

determined mainly by morphological traits, but these growth rates are maintained at the expense of defense and storage allocation. As we could observe, SI species suffered from selective herbivory by cattle (i.e., leaves of trees from SI species were eaten; whereas those of PT-ST were not). On the other hand, as mentioned by the same author, survival of SI species cannot be attributed to a high net C balance By age 7, the crown of SI species were in contact and forming an upper layer of dominant trees; whereas, PT and ST species conformed an intermediate layer. Although competition for light was not evident from the observed crown ratio values; the SI trees showed a large loss of leaves on their lower branches; whereas these persisted in trees of PT and ST, keeping large crown ratios despite being shaded. Only, between ages 5 and 7, the shade created by the new plantation has eradicated pastures, except in sites canopy holes created by tree mortality or in the borders of the planted sites. Natural regeneration of some tree and shrub species began after year two, and when taken into account increase stand density above 100%. In highly shaded areas, the presence of herbaceous plants is rather scarce and a fine layer of

Our research with tree native species and establishment of demonstrative trials

The most critical aspects for the initial success of these plantations consists on maintaining cattle exclusion for at least five years after establishment, irrigating during the first dry season, and keeping control of grasses and vines at least for two years. Different mixed shade tolerance groups of tree species can stand conditions of sites dominated by pastures under high level of sunlight exposure; however, SI species appear to have faster growth rates than PT or ST species independently of

*State of development of one of the mixed plantations: (a) one year old, (b) 2 years old, (c) 4.5 years old,* 

in cloud forests show promising that reforesting with native species is a viable alternative for restoring degraded areas and the recovery of tree biodiversity given

adequate planning, management and monitoring (**Figure 5**).

**36**

**Figure 5.**

*(d) 7 years old.*

We are grateful to Ancelmo Dugarte and Dani Dugarte for their invaluable assistance in fieldwork. This work was partially funded by Consejo de Desarrollo Científico, Humanístico, Tecnológico y de las Artes, University of Los Andes (CDCHTA-ULA) (Grant F0–746–17–01-A).

#### **Conflict of interest**

The authors declare no conflict of interest.

#### **Author details**

Ana Quevedo-Rojas\* and Mauricio Jerez-Rico Facultad de Ciencias Forestales y Ambientales, University of Los Andes, Mérida, Venezuela

\*Address all correspondence to: anamer2@gmail.com

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

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[2] Lamb D, Erskine PD, Parrotta JA. Restoration of degraded tropical forest landscapes. Science. 2005;310(5754): 1628-1632.

[3] Chazdon RL. Beyond Deforestation: Restoring Forests and Ecosystem Services on Degraded Lands Science. 2008;320:1458-1460.

[4] Trujillo-Miranda AL, Toledo-Aceves T, López-Barrera F, Gerez-Fernández P. Active versus passive restoration: Recovery of cloud forest structure, diversity and soil condition in abandoned pastures. Ecol Eng. 2018 Jul;117:50-61.

[5] Holl KD, Aide TM. When and where to actively restore ecosystems? For Ecol Manag. 2011 May;261(10):1558-63.

[6] Liu CLC, Kuchma O, Krutovsky KV. Mixed-species versus monocultures in plantation forestry: Development, benefits, ecosystem services and perspectives for the future. Glob Ecol Conserv. 2018 Jul;15:e00419.

[7] Petit B, Montagnini F. Growth in pure and mixed plantations of tree species used in reforesting rural areas of the humid region of Costa Rica, Central America. For Ecol Manag. 2006;233(2-3):338-343.

[8] Schwarzkopf T, Riha SJ, Fahey TJ, Degloria S. Are cloud forest tree structure and environment related in the Venezuelan Andes?: CLOUD

FOREST STRUCTURE IN THE ANDES. Austral Ecol. 2011 May;36(3):280-9.

[9] Quevedo-Rojas A, Jerez-Rico M, Schwarzkopf Kratzer T, García-Núñez C. Distribution of juveniles of tree species along a canopy closure gradient in a tropical cloud forest of the Venezuelan Andes. IForest - Biogeosciences For. 2016 Jun 1;9(3):363-9.

[10] Quevedo-Rojas AM, Schwarzkopf T, García C, Jerez-Rico M. Ambiente de luz del sotobosque de una selva nublada andina: efectos de la estructura del dosel y la estacionalidad climática. Rev Biol Trop [Internet]. 2016 Jul 20 [cited 2020 Oct 12];64(4). Available from: http:// revistas.ucr.ac.cr/index.php/rbt/article/ view/21861

[11] García-Núñez C, Azócar A, Rada F. Photosynthetic acclimation to light in juveniles of two cloud forest tree species. Trees. 1995 Dec 1;10(2):114-24.

[12] Quevedo-Rojas A, García-Núñez C, Jerez-Rico M, Jaimez R, Schwarzkopf T. Leaf acclimation strategies to contrasting light conditions in saplings of different shade tolerance in a tropical cloud forest. Funct Plant Biol. 2018;45(9):968.

[13] Ramos MC, Plonczak M. Dinámica sucesional del componente arbóreo, luego de un estudio destructivo de biomasa, en el bosque universitario San Eusebio, Mérida-Venezuela. Rev For Venez. 2007;51(1):35-46.

[14] Ataroff M, Rada F. Deforestation Impact on Water Dynamics in a Venezuelan Andean Cloud Forest. AMBIO J Hum Environ. 2000 Nov; 29(7):440-4.

[15] Ataroff M. VENEZUELA. In: BOSQUES NUBLADOS DEL NEOTROPICO. INBIO; 2001. p. 397-442.

[16] Gonsamo A, D'odorico P, Pellikka P. Measuring fractional forest canopy

**39**

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests…*

[24] Di Rienzo JA, Macchiavelli R, Casanoves F. Modelos Mixtos en InfoStat. Córdoba, Argentina: Grupo

[25] Stroup WW. Rethinking the Analysis of Non-Normal Data in Plant and Soil Science. Agron J. 2015

[26] Littell RC, Milliken GA, Stroup WW, Wolfinger RD, Schabenberger O. SAS for Mixed Models, Second Ed. SAS

[27] López-Barrera F, Rojas-Soto O, Montes-Hernández B, Aguirre A, Aguilar-Dorantes K, Landgrave R, et al. Ecología de la restauración del bosque nublado en el centro de Veracruz. In: Experiencias mexicanas en la restauración de los ecosistemas (Mexican experiences in ecosystem restoration). 1st ed. UNAM-CRIM, UAEM, CONABIOEditors: Eliane Ceccon, Cristina Martínez-Garza; 2016.

[28] Avendaño-Yáñez M de la L, Sánchez-Velásquez LR, Meave JA, Pineda-López M del R. Is facilitation a promising strategy for cloud forest restoration? For Ecol Manag. 2014

[29] Coelho GC, Benvenutti-Ferreira, G, Schirmer, J, Luchesse OA. Survival, growth and seed mass in a mixed tree species planting for Atlantic Forest restoration. AIMS Environ Sci.

INFOSTAT; 2012.

Mar;107(2):811-27.

p. 30.

Oct;329:328-33.

2016;3(3):382-94.

[30] Martínez-Camilo R, González-Espinosa M,

Ramírez-Marcial N, Cayuela L,

[31] Laurans M, Vincent G. Are inter- and intraspecific variations of sapling crown traits consistent with

Pérez-Farrera MÁ. Tropical tree species diversity in a mountain system in southern Mexico: local and regional patterns and determinant factors. Biotropica. 2018 May;50(3):499-509.

Institute, Cary, NC. 2006.

*DOI: http://dx.doi.org/10.5772/intechopen.95006*

element cover and openness - definitions and methodologies revisited. Oikos.

2013 Sep;122(9):1283-91.

pdf

[17] Frazer GW, Canham CD, Lertzman KP. Gap Light Analyzer (GLA), Version 2.0: Imaging software to extract canopy structure and gap light transmission indices from true-colour fisheye photographs, users manual and program documentation. Simon Fraser Univ Burnaby Br Columbia Inst Ecosyst Stud Millbrook N Y. 1999;36. Available from: http://rem.sfu.ca/forestry/ downloads/Files/GLAV2UsersManual.

[18] Zhang Y, Chen JM, Miller JR. Determining digital hemispherical photograph exposure for leaf area index estimation. Agric For Meteorol.

[19] Ezenwenyi JU, Chukwu O. Effects Of Slenderness Coefficient In Crown Area Prediction For Tectona Grandis Linn. F. In Omo Forest Reserve,

Nigeria. Current Life Sciences. 2017 Sep

Zhang J. Effects of competition, age and climate on tree slenderness of Chinese fir plantations in southern China. For Ecol Manag. 2020 Feb;458:117815.

Vásquez-Grandón A, González-Chang M,

[22] Zhao D, Kane M, Borders BE. Crown Ratio and Relative Spacing Relationships for Loblolly Pine Plantations. Open J

[23] SAS Institute, SAS/STAT user's guide, version 9.1. Cary, NC: SAS

[20] Zhang X, Wang H, Chhin S,

Salas-Eljatib C. Differential Early Performance of Two Underplanted Hardwood Tree Species Following Restoration Treatments in High-Graded Temperate Rainforests. Forests. 2020 Apr

[21] Soto DP, Donoso PJ,

For. 2012;02(03):101-15.

Institute; 2004.

2005;133(1):166-181.

25;3(4):65-71

3;11(4):401.

*Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests… DOI: http://dx.doi.org/10.5772/intechopen.95006*

element cover and openness - definitions and methodologies revisited. Oikos. 2013 Sep;122(9):1283-91.

[17] Frazer GW, Canham CD, Lertzman KP. Gap Light Analyzer (GLA), Version 2.0: Imaging software to extract canopy structure and gap light transmission indices from true-colour fisheye photographs, users manual and program documentation. Simon Fraser Univ Burnaby Br Columbia Inst Ecosyst Stud Millbrook N Y. 1999;36. Available from: http://rem.sfu.ca/forestry/ downloads/Files/GLAV2UsersManual. pdf

[18] Zhang Y, Chen JM, Miller JR. Determining digital hemispherical photograph exposure for leaf area index estimation. Agric For Meteorol. 2005;133(1):166-181.

[19] Ezenwenyi JU, Chukwu O. Effects Of Slenderness Coefficient In Crown Area Prediction For Tectona Grandis Linn. F. In Omo Forest Reserve, Nigeria. Current Life Sciences. 2017 Sep 25;3(4):65-71

[20] Zhang X, Wang H, Chhin S, Zhang J. Effects of competition, age and climate on tree slenderness of Chinese fir plantations in southern China. For Ecol Manag. 2020 Feb;458:117815.

[21] Soto DP, Donoso PJ, Vásquez-Grandón A, González-Chang M, Salas-Eljatib C. Differential Early Performance of Two Underplanted Hardwood Tree Species Following Restoration Treatments in High-Graded Temperate Rainforests. Forests. 2020 Apr 3;11(4):401.

[22] Zhao D, Kane M, Borders BE. Crown Ratio and Relative Spacing Relationships for Loblolly Pine Plantations. Open J For. 2012;02(03):101-15.

[23] SAS Institute, SAS/STAT user's guide, version 9.1. Cary, NC: SAS Institute; 2004.

[24] Di Rienzo JA, Macchiavelli R, Casanoves F. Modelos Mixtos en InfoStat. Córdoba, Argentina: Grupo INFOSTAT; 2012.

[25] Stroup WW. Rethinking the Analysis of Non-Normal Data in Plant and Soil Science. Agron J. 2015 Mar;107(2):811-27.

[26] Littell RC, Milliken GA, Stroup WW, Wolfinger RD, Schabenberger O. SAS for Mixed Models, Second Ed. SAS Institute, Cary, NC. 2006.

[27] López-Barrera F, Rojas-Soto O, Montes-Hernández B, Aguirre A, Aguilar-Dorantes K, Landgrave R, et al. Ecología de la restauración del bosque nublado en el centro de Veracruz. In: Experiencias mexicanas en la restauración de los ecosistemas (Mexican experiences in ecosystem restoration). 1st ed. UNAM-CRIM, UAEM, CONABIOEditors: Eliane Ceccon, Cristina Martínez-Garza; 2016. p. 30.

[28] Avendaño-Yáñez M de la L, Sánchez-Velásquez LR, Meave JA, Pineda-López M del R. Is facilitation a promising strategy for cloud forest restoration? For Ecol Manag. 2014 Oct;329:328-33.

[29] Coelho GC, Benvenutti-Ferreira, G, Schirmer, J, Luchesse OA. Survival, growth and seed mass in a mixed tree species planting for Atlantic Forest restoration. AIMS Environ Sci. 2016;3(3):382-94.

[30] Martínez-Camilo R, González-Espinosa M, Ramírez-Marcial N, Cayuela L, Pérez-Farrera MÁ. Tropical tree species diversity in a mountain system in southern Mexico: local and regional patterns and determinant factors. Biotropica. 2018 May;50(3):499-509.

[31] Laurans M, Vincent G. Are inter- and intraspecific variations of sapling crown traits consistent with

**38**

*Silviculture*

**References**

1628-1632.

2008;320:1458-1460.

[1] Paula RR, de Oliveira IR, Gonçalves JL de M, de Vicente Ferraz A. Why Mixed Forest Plantation? In: Bran Nogueira Cardoso EJ, Gonçalves JL de M, Balieiro F de C, Franco AA, editors. Mixed Plantations of Eucalyptus and Leguminous Trees [Internet]. Cham: Springer International Publishing; 2020 [cited 2020 Oct 12]. p. 1-13. Available from: http://link.springer. com/10.1007/978-3-030-32365-3\_1

FOREST STRUCTURE IN THE ANDES. Austral Ecol. 2011 May;36(3):280-9.

[10] Quevedo-Rojas AM, Schwarzkopf T, García C, Jerez-Rico M. Ambiente de luz del sotobosque de una selva nublada andina: efectos de la estructura del dosel y la estacionalidad climática. Rev Biol Trop [Internet]. 2016 Jul 20 [cited 2020 Oct 12];64(4). Available from: http:// revistas.ucr.ac.cr/index.php/rbt/article/

[11] García-Núñez C, Azócar A, Rada F. Photosynthetic acclimation to light in juveniles of two cloud forest tree species. Trees. 1995 Dec 1;10(2):114-24.

[12] Quevedo-Rojas A, García-Núñez C, Jerez-Rico M, Jaimez R, Schwarzkopf T. Leaf acclimation strategies to contrasting light conditions in saplings of different shade tolerance in a tropical cloud forest. Funct Plant Biol. 2018;45(9):968.

[13] Ramos MC, Plonczak M. Dinámica sucesional del componente arbóreo, luego de un estudio destructivo de biomasa, en el bosque universitario San Eusebio, Mérida-Venezuela. Rev For

[14] Ataroff M, Rada F. Deforestation Impact on Water Dynamics in a Venezuelan Andean Cloud Forest. AMBIO J Hum Environ. 2000 Nov;

NEOTROPICO. INBIO; 2001. p. 397-442.

[16] Gonsamo A, D'odorico P, Pellikka P. Measuring fractional forest canopy

Venez. 2007;51(1):35-46.

[15] Ataroff M. VENEZUELA. In: BOSQUES NUBLADOS DEL

29(7):440-4.

[9] Quevedo-Rojas A, Jerez-Rico M, Schwarzkopf Kratzer T, García-Núñez C. Distribution of juveniles of tree species along a canopy closure gradient in a tropical cloud forest of the Venezuelan Andes. IForest - Biogeosciences For. 2016

Jun 1;9(3):363-9.

view/21861

[2] Lamb D, Erskine PD, Parrotta JA. Restoration of degraded tropical forest landscapes. Science. 2005;310(5754):

[3] Chazdon RL. Beyond Deforestation: Restoring Forests and Ecosystem Services on Degraded Lands Science.

[4] Trujillo-Miranda AL, Toledo-Aceves T, López-Barrera F, Gerez-Fernández P. Active versus passive restoration: Recovery of cloud forest structure, diversity and soil condition in abandoned pastures. Ecol Eng. 2018 Jul;117:50-61.

[5] Holl KD, Aide TM. When and where to actively restore ecosystems? For Ecol Manag. 2011 May;261(10):1558-63.

[6] Liu CLC, Kuchma O, Krutovsky KV. Mixed-species versus monocultures in plantation forestry: Development, benefits, ecosystem services and perspectives for the future. Glob Ecol

Conserv. 2018 Jul;15:e00419.

2006;233(2-3):338-343.

[7] Petit B, Montagnini F. Growth in pure and mixed plantations of tree species used in reforesting rural areas of the humid region of Costa Rica, Central America. For Ecol Manag.

[8] Schwarzkopf T, Riha SJ, Fahey TJ, Degloria S. Are cloud forest tree structure and environment related in the Venezuelan Andes?: CLOUD

a strategy promoting light capture in tropical moist forest? Ann Bot. 2016 Oct;118(5):983-96.

[32] Kitajima K. Relative importance of photosynthetic traits and allocation patterns as correlates of seedling shade tolerance of 13 tropical trees. Oecologia. 1994 Aug;98(3-4):419-28.

[33] Wilson SJ, Rhemtulla JM. Acceleration and novelty: community restoration speeds recovery and transforms species composition in Andean cloud forest. Ecol Appl. 2016 Jan;26(1):203-18.

**41**

**Chapter 3**

**Abstract**

**1. Introduction**

diversity.

*Ana Cristina Gonçalves*

Thinning: An Overview

Thinning is one of the primordial silvicultural practices. It has been analysed by its methods and intensities, associated to the tree selection criteria. Yet, while some methods are of generalised use, others were developed for specific purposes. The goal of this review is to compile the existing information regarding tree selection, thinning methods and intensity as well as their effects on trees and stands. The effects of thinning indicate a reduction of density and a trend towards an increase of growth rates at tree level for a short time after thinning. Biomass and volume show similar or smaller values when compared to unthinned stands. Mortality and growth stagnation, especially in stands with low stability or vigour, can also occur. The modifications in stand structure can enhance its role as an adaptive measure.

Stand and forest management encompasses a set of silvicultural practices which are designed according to its goals. Among these, thinning is of primordial importance as it influences stand structure, tree and stand growth, products, yields and

In time, the trees of a stand occupy gradually the available growing space, developing simultaneously facilitation and competitive interactions [1]. The balance between these two interactions is dynamic, but competition increases with the decrease of the growing space. The result is that individuals with competitive advantages reallocate the growing space formerly occupied by other individuals with less competitive advantages and suppress them. This originates from the development of a social structure which, when growing space is fully occupied, derives

Thinning implies always the removal of trees with the main goal of allocating the growing space to those better suited to the desired productions and yields [2–6]. The removal of trees can have both positive and negative effects. The positive, are related to the reduction of competition, anticipation of volume losses due to self-thinning, increase of diameter growth rate, increase of timber value and revenue and reduction of the damages due to the abiotic and biotic disturbances. The negative, are associated with the reduction of total volume, risk of mortality or growth stagnation, cost of the operation, damages in the remaining trees and risk of

In literature, thinning has been analysed according to its method and intensity as well as with the tree selection criteria. Yet, while some methods are of generalised use, others were developed for specific purposes. The main goal of this review is to compile the existing information regarding tree selection, thinning methods and

in the death of the suppressed individuals, that is, self-thinning [2].

damages by abiotic and biotic agents [2, 6].

**Keywords:** method, intensity, stand structure, growth, adaptive measure

## **Chapter 3** Thinning: An Overview

*Ana Cristina Gonçalves*

#### **Abstract**

*Silviculture*

Oct;118(5):983-96.

Jan;26(1):203-18.

1994 Aug;98(3-4):419-28.

[33] Wilson SJ, Rhemtulla JM.

Acceleration and novelty: community restoration speeds recovery and transforms species composition in Andean cloud forest. Ecol Appl. 2016

a strategy promoting light capture in tropical moist forest? Ann Bot. 2016

[32] Kitajima K. Relative importance of photosynthetic traits and allocation patterns as correlates of seedling shade tolerance of 13 tropical trees. Oecologia.

**40**

Thinning is one of the primordial silvicultural practices. It has been analysed by its methods and intensities, associated to the tree selection criteria. Yet, while some methods are of generalised use, others were developed for specific purposes. The goal of this review is to compile the existing information regarding tree selection, thinning methods and intensity as well as their effects on trees and stands. The effects of thinning indicate a reduction of density and a trend towards an increase of growth rates at tree level for a short time after thinning. Biomass and volume show similar or smaller values when compared to unthinned stands. Mortality and growth stagnation, especially in stands with low stability or vigour, can also occur. The modifications in stand structure can enhance its role as an adaptive measure.

**Keywords:** method, intensity, stand structure, growth, adaptive measure

#### **1. Introduction**

Stand and forest management encompasses a set of silvicultural practices which are designed according to its goals. Among these, thinning is of primordial importance as it influences stand structure, tree and stand growth, products, yields and diversity.

In time, the trees of a stand occupy gradually the available growing space, developing simultaneously facilitation and competitive interactions [1]. The balance between these two interactions is dynamic, but competition increases with the decrease of the growing space. The result is that individuals with competitive advantages reallocate the growing space formerly occupied by other individuals with less competitive advantages and suppress them. This originates from the development of a social structure which, when growing space is fully occupied, derives in the death of the suppressed individuals, that is, self-thinning [2].

Thinning implies always the removal of trees with the main goal of allocating the growing space to those better suited to the desired productions and yields [2–6]. The removal of trees can have both positive and negative effects. The positive, are related to the reduction of competition, anticipation of volume losses due to self-thinning, increase of diameter growth rate, increase of timber value and revenue and reduction of the damages due to the abiotic and biotic disturbances. The negative, are associated with the reduction of total volume, risk of mortality or growth stagnation, cost of the operation, damages in the remaining trees and risk of damages by abiotic and biotic agents [2, 6].

In literature, thinning has been analysed according to its method and intensity as well as with the tree selection criteria. Yet, while some methods are of generalised use, others were developed for specific purposes. The main goal of this review is to compile the existing information regarding tree selection, thinning methods and

intensity as well as their effects on trees and stands. The chapter is organised in four sections. Section 2 describes and characterises tree selection criteria. Section 3 analyses the thinning methods and intensity. Section 4 analyses the effects of thinning on stand structure, growth, products and as an adaptive measure.

#### **2. Tree selection**

Tree selection plays one of the key roles in thinning, as one of its main objectives is the reallocation of growing space to a set of trees in the stand. Care has to be taken so that the trees maintained in the stand are able to use the growing space made available [2, 6, 7]. Thus, it has to be thought at two complementary levels: (i) at tree level, reallocating the growing space to the trees kept so that they reach the desired growth rates, yields and product quality and (ii) at stand level, optimising yield for the desired production cycle, which is also related to density, spatial arrangement and site quality. These levels derive from two tree development traits, namely, the intrinsic and the external. The former is mainly driven by genetics, preponderant when trees grow isolated. In the latter, the growing space availability determines trees development [1, 2, 8]. These complementary objectives enable balancing interactions to achieve growing space use optimization and improve the overall stand quality and yield.

The need of selecting trees enhanced the development of tools to evaluate growing stock, stability, potential photosynthetic ability and growth rate [1–3, 6, 9]. One of the mostly used is the tree classification system. Their main advantages are that tree and stand description, evaluation and monitoring (both spatial and temporal) can be carried out with a set of qualitative criteria, needless of forest inventories. The stand evaluation is quick with low costs and helps to implement silvicultural practices. The disadvantages are related to their development or adaptation to stand structure and management goals, to not enabling a quantitative evaluation and to the need of skilled practitioners [2, 6–8, 10].

Due to the variety of stand structures and management goals, many tree classification systems were developed. They evolved in time, increasing in complexity, as more criteria were included to increase accuracy and precision [7, 8, 11]. Typically, tree classification systems are grouped in two broad classes according to the stand structure and production goals. One is directed towards pure even-aged stands with one main production (timber), for example, of kraft [10], of 1902 [10], English [12], of Assmann [2], Belgian [3], of Meadows and Skojac [11]. The other is directed to pure or mixed uneven-aged systems with one main production or several ones, for example, of Assmann [2], of Florence [8], of IUFRO [7], of Meadows [13] and of Perkey classification [14].

The concept of future trees is related to tree characteristics, moment of selection, number of trees per unit area and their spatial arrangements.

The criteria associated with the future tree characteristics referred in independent studies (e.g. [3, 6, 7, 15–19]) are similar, and eight criteria can be pointed out: (i) vigour and good sanitary conditions, (ii) social position (dominant or codominant), (iii) suitability of the species mixture, (iv) vertical straight stem, (v) without stem deformation (forks) up to 6–8 m for timber and 2–4 m for bark and fruit production, (vi) wood without serious defects, (vii) final ramification, few small branches in the case of timber production and to be promoted to increase production in the case of bark and fruit and (viii) balanced crown. These criteria can be totally or partially used depending on the management and production goals.

The moment to designate the future trees is not consensual, however, some guidelines have been reported [3, 7, 17, 19]: (i) social position maintenance – young

**43**

*Thinning: An Overview*

*DOI: http://dx.doi.org/10.5772/intechopen.93436*

selection later, for example, after 30–40 years [3, 4, 7].

ing on the species ecological and cultural characteristics [4, 7].

**3. Thinning method and intensity**

crown release and variable density thinning.

limited reaction to release [6].

in the later stages of development [6].

trees have higher probability of social regression than adult ones; (ii) species tolerance to shade – shade-tolerant trees are able to live suppressed and, after release, are able to ascend to dominant positions whether intolerant are not; (iii) low risk of sudden death or break and free of wounds – trees should be vigorous, stable, in good sanitary conditions and without injuries; (iv) stability – trees should be stable enough so that after release they are able to develop with low probability of falling down and (v) longevity – it should be ensured that they are able to reach the end of the production cycle. The selection should then be made as earlier as possible, as soon as the probability of changing social status is low. It can be done when trees reach 10–25 cm of diameter at breast height [3, 17], or 20 m of dominant height [17] or 10–14 m of stem height [17]. When it is convenient to designate future trees very early in time, a preselection of the future trees is recommended, followed by their

The number of trees per unit area is determined by the release from the competition of the future trees during the entire production cycle, to optimise their development. A density between 80 and 250 trees ha−1 is suggested [4, 7]. The better the site quality and the shorter the production cycle, the higher their number. The larger the crowns and the lower the shade tolerance, the lower their number [7]. The spatial arrangement of the future trees should be uniform to enable a more efficient and complete use of the growing space while maintaining the growth rate at highest desired levels, which corresponds to a mean spacing of ≈7–12 m, depend-

Thinning method or type can be defined by the classes and social position of the removed trees, although other parameters such as stem and crown characteristics are also important [2–6]. Nine methods have been identified, namely from below, from above, selective or Schädelin, of dominants, mechanical, free, compensation,

*Thinning from the below* main goal is to favour the best trees of the upper layer, of better dimensions and crowns. The removal of the individuals starts with the dead, dying and dominated, and only if necessary the codominant and dominant individuals (mainly, individuals of bad characteristics) are removed. It has low effect in the subsequent growth of the remaining stand. Thus, it only anticipates the normal pattern of tree senescence and dead in an unthinned stand. It is suited for sites where water is a limiting factor [2–6]. The best results are attained with intolerant species, where the stems of the inferior layers do not have or only have a

*Thinning from the above* main goal is to favour the best trees of the upper layer until the end of rotation. The trees to be removed are predominantly in the upper layer and in direct competition with the best trees. The inferior layers are maintained with the objectives of enhancing natural pruning, soil protection, reducing spontaneous vegetation development, increasing resistance to wind and maintaining or enhancing wildlife habitat. However, the tree removal in the inferior layers can be considered for aesthetical reasons or to reduce the risk of fire, creating vertical discontinuity [2–6]. It is better suited for shade or semi-shade-tolerant species, in pure and mixed stands, especially when quality trees are found in an adequate number in the superior layers. It is not suited for shade-intolerant species, especially

*Selective* or *Schädelin thinning's* main assumption is the selection of the future

trees. They can be selected in all social classes, according to a set of criteria

#### *Thinning: An Overview DOI: http://dx.doi.org/10.5772/intechopen.93436*

*Silviculture*

**2. Tree selection**

stand quality and yield.

of Perkey classification [14].

the need of skilled practitioners [2, 6–8, 10].

intensity as well as their effects on trees and stands. The chapter is organised in four sections. Section 2 describes and characterises tree selection criteria. Section 3 analyses the thinning methods and intensity. Section 4 analyses the effects of thin-

Tree selection plays one of the key roles in thinning, as one of its main objectives is the reallocation of growing space to a set of trees in the stand. Care has to be taken so that the trees maintained in the stand are able to use the growing space made available [2, 6, 7]. Thus, it has to be thought at two complementary levels: (i) at tree level, reallocating the growing space to the trees kept so that they reach the desired growth rates, yields and product quality and (ii) at stand level, optimising yield for the desired production cycle, which is also related to density, spatial arrangement and site quality. These levels derive from two tree development traits, namely, the intrinsic and the external. The former is mainly driven by genetics, preponderant when trees grow isolated. In the latter, the growing space availability determines trees development [1, 2, 8]. These complementary objectives enable balancing interactions to achieve growing space use optimization and improve the overall

The need of selecting trees enhanced the development of tools to evaluate growing stock, stability, potential photosynthetic ability and growth rate [1–3, 6, 9]. One of the mostly used is the tree classification system. Their main advantages are that tree and stand description, evaluation and monitoring (both spatial and temporal) can be carried out with a set of qualitative criteria, needless of forest inventories. The stand evaluation is quick with low costs and helps to implement silvicultural practices. The disadvantages are related to their development or adaptation to stand structure and management goals, to not enabling a quantitative evaluation and to

Due to the variety of stand structures and management goals, many tree classification systems were developed. They evolved in time, increasing in complexity, as more criteria were included to increase accuracy and precision [7, 8, 11]. Typically, tree classification systems are grouped in two broad classes according to the stand structure and production goals. One is directed towards pure even-aged stands with one main production (timber), for example, of kraft [10], of 1902 [10], English [12], of Assmann [2], Belgian [3], of Meadows and Skojac [11]. The other is directed to pure or mixed uneven-aged systems with one main production or several ones, for example, of Assmann [2], of Florence [8], of IUFRO [7], of Meadows [13] and

The concept of future trees is related to tree characteristics, moment of selec-

The criteria associated with the future tree characteristics referred in independent studies (e.g. [3, 6, 7, 15–19]) are similar, and eight criteria can be pointed out: (i) vigour and good sanitary conditions, (ii) social position (dominant or codominant), (iii) suitability of the species mixture, (iv) vertical straight stem, (v) without stem deformation (forks) up to 6–8 m for timber and 2–4 m for bark and fruit production, (vi) wood without serious defects, (vii) final ramification, few small branches in the case of timber production and to be promoted to increase production in the case of bark and fruit and (viii) balanced crown. These criteria can be totally or partially used depending on the management and production goals. The moment to designate the future trees is not consensual, however, some guidelines have been reported [3, 7, 17, 19]: (i) social position maintenance – young

tion, number of trees per unit area and their spatial arrangements.

ning on stand structure, growth, products and as an adaptive measure.

**42**

trees have higher probability of social regression than adult ones; (ii) species tolerance to shade – shade-tolerant trees are able to live suppressed and, after release, are able to ascend to dominant positions whether intolerant are not; (iii) low risk of sudden death or break and free of wounds – trees should be vigorous, stable, in good sanitary conditions and without injuries; (iv) stability – trees should be stable enough so that after release they are able to develop with low probability of falling down and (v) longevity – it should be ensured that they are able to reach the end of the production cycle. The selection should then be made as earlier as possible, as soon as the probability of changing social status is low. It can be done when trees reach 10–25 cm of diameter at breast height [3, 17], or 20 m of dominant height [17] or 10–14 m of stem height [17]. When it is convenient to designate future trees very early in time, a preselection of the future trees is recommended, followed by their selection later, for example, after 30–40 years [3, 4, 7].

The number of trees per unit area is determined by the release from the competition of the future trees during the entire production cycle, to optimise their development. A density between 80 and 250 trees ha−1 is suggested [4, 7]. The better the site quality and the shorter the production cycle, the higher their number. The larger the crowns and the lower the shade tolerance, the lower their number [7].

The spatial arrangement of the future trees should be uniform to enable a more efficient and complete use of the growing space while maintaining the growth rate at highest desired levels, which corresponds to a mean spacing of ≈7–12 m, depending on the species ecological and cultural characteristics [4, 7].

#### **3. Thinning method and intensity**

Thinning method or type can be defined by the classes and social position of the removed trees, although other parameters such as stem and crown characteristics are also important [2–6]. Nine methods have been identified, namely from below, from above, selective or Schädelin, of dominants, mechanical, free, compensation, crown release and variable density thinning.

*Thinning from the below* main goal is to favour the best trees of the upper layer, of better dimensions and crowns. The removal of the individuals starts with the dead, dying and dominated, and only if necessary the codominant and dominant individuals (mainly, individuals of bad characteristics) are removed. It has low effect in the subsequent growth of the remaining stand. Thus, it only anticipates the normal pattern of tree senescence and dead in an unthinned stand. It is suited for sites where water is a limiting factor [2–6]. The best results are attained with intolerant species, where the stems of the inferior layers do not have or only have a limited reaction to release [6].

*Thinning from the above* main goal is to favour the best trees of the upper layer until the end of rotation. The trees to be removed are predominantly in the upper layer and in direct competition with the best trees. The inferior layers are maintained with the objectives of enhancing natural pruning, soil protection, reducing spontaneous vegetation development, increasing resistance to wind and maintaining or enhancing wildlife habitat. However, the tree removal in the inferior layers can be considered for aesthetical reasons or to reduce the risk of fire, creating vertical discontinuity [2–6]. It is better suited for shade or semi-shade-tolerant species, in pure and mixed stands, especially when quality trees are found in an adequate number in the superior layers. It is not suited for shade-intolerant species, especially in the later stages of development [6].

*Selective* or *Schädelin thinning's* main assumption is the selection of the future trees. They can be selected in all social classes, according to a set of criteria

(cf. Section 2). The thinning is focused on the release of the future trees, with the removal of all competitors and the maintenance of trees that can be useful or do not interfere with them. Also, the future trees should have, as much as possible, a uniform spacing. Its selection is not static in time, especially in young development stages. Thus, before each thinning they have to be checked and, if necessary, reselected [7, 20, 21]. The main goal of this thinning is the optimization of the production in value rather than in volume, favouring at the same time the mechanical and ecological stability [7, 20].

*Thinning of dominants* is focused on the upper layers. The dominant and the codominant trees are removed, including the more promising and those of the intermediate and inferior layers are favoured. It is suited for a reduced set of objectives, and care should be taken so that it does not derive in the harvest of the best trees. Three approaches can be considered, as a function of the objectives and number interventions [6]:


*Mechanical* or *geometric thinning* is associated to large spacing silviculture with selected material, in which the removal of a tree is more related with its location than with its position, because the goal is to maintain a regular cover. It is advantageous in young, very dense unthinned stands. Two subtypes can be identified: *spacing*, where the trees at a certain distance of the selected tree are removed; and *row* or *strip*, where the individuals of one or several lines are removed [6].

*Free thinning* goal is the selection of a set of trees which are maintained in free growth until the end of the rotation in order to produce high quantity of timber with high quality [22]. It is directed to oak species and rotations of less than 100 years. It begins with the selection of the future trees with a density of 60–80 trees ha−1, uniformly spaced. It is followed by the removal of all the trees whose crown distance from a future tree is less than 25% of the mean crown width (assumption to be maintained throughout rotation, to keep future trees in free growth). As a secondary silvicultural practice, pruning is recommended up to a height of 6 m as well as removing the epicormic branches [22, 23]. It has also

**45**

*Thinning: An Overview*

*DOI: http://dx.doi.org/10.5772/intechopen.93436*

(≈370 trees ha−1).

the competition.

or fourth row).

been used in mixtures of conifers and oaks, and oaks in pure or mixed stands with

*Compensation thinning's* (*éclairci de ratrapage*) aim is favouring the future trees that have sufficient stability and well-balanced crowns, being less important in their spatial distribution and their optimal distance. It is frequently linked with the goal of keeping stand stability and should have light intensity. It is preferred in stands without or with thinnings of low intensity in the past. In these cases, only the dominant stems are able to react to release, and thus codominant individuals should be preferably removed. It is especially suited for stands in steep slope areas where it is easy to overestimate distances due to crown overlapping and asymmetry [7]. *Crown releasing thinning's* (*éclairci misse en lumiére*) main goal is regulating future trees in old growth development stage. The trees' metabolism and growth, capacity of reaction to release and ability to redo their crowns are lower than in the mature ones. The social positions are nearly definite, and the probability of individuals of the inferior social classes to ascend to upper classes is low. Future trees are released from competition from those of the intermediate layers as the dominant competitors were removed in the former thinnings. The objective is to maintain or increase diameter growth, to allow the largest possible increase of productivity in value. The intensity should be light and periodicity should be long, according to the trees' growth rates [7]. *Variable density thinning's* goal is to promote variability and heterogeneity, both spatial (horizontal and vertical) and structural [25–28], as well as stimulate latesuccessional forest structures, reduce stand density, alter species composition [25, 26, 29] and be a restauration tool [27, 30, 31]. It assumes the unevenly removal of trees, creating gradients of density in the stand. This is implemented with the creation of patches with variable spatial distribution, where canopy gaps and patches of different densities coexist [26, 27, 32]. The proportion of each patch type is also variable according to the intended complexity of stand structure, the existing stand structure, the species composition and spatial arrangement [31, 32]. Six protocols are referred, which due to their similarities were grouped in four types [32]:

i.*Randomised grid*: Stand area is divided in a grid with cells of equal area and the number of individuals to be maintained is randomly sorted. Two target densities can be chosen, low (≈185 trees ha−1) and moderate

ii.*Dx rule*: Selected trees define density depending on site variability and tree dimensions. The area of influence of each selected tree is defined by a circle proportional to the diameter at breast height by k-fold (e.g. k = 2). In this area, trees between a diameter range are removed, while those outside it are kept. The upper and lower thresholds can be defined per stand or per

iii. *Spacing thinning*: Stand area is divided in a square point grid (e.g. ≈5 × 5 or 6 × 6 m) as well as a buffer for each point (e.g*.* ≈1.2 m). For each buffer area, the best tree larger than a diameter threshold is selected and released from

iv.*Localised release*: Stand area is divided in a point square grid associated to a buffer (e.g*.* 7.6 m of radius). In each circular area, three trees are selected irrespective of their spatial arrangement with the same rules as the former type, while the areas outside the buffers are either thinned with about 3.6 m spacing in the row space outside the buffers or remain unthinned (e.g*.* third

species. The areas outside the circles are not thinned.

*Fraxinus excelsior*, *Acer pseudoplatanus* and *Prunus avium* [24].

#### *Thinning: An Overview DOI: http://dx.doi.org/10.5772/intechopen.93436*

*Silviculture*

ecological stability [7, 20].

number interventions [6]:

(cf. Section 2). The thinning is focused on the release of the future trees, with the removal of all competitors and the maintenance of trees that can be useful or do not interfere with them. Also, the future trees should have, as much as possible, a uniform spacing. Its selection is not static in time, especially in young development stages. Thus, before each thinning they have to be checked and, if necessary, reselected [7, 20, 21]. The main goal of this thinning is the optimization of the production in value rather than in volume, favouring at the same time the mechanical and

*Thinning of dominants* is focused on the upper layers. The dominant and the codominant trees are removed, including the more promising and those of the intermediate and inferior layers are favoured. It is suited for a reduced set of objectives, and care should be taken so that it does not derive in the harvest of the best trees. Three approaches can be considered, as a function of the objectives and

i.Thinning of dominants *with temporary character*: The goal is to improve the overall stand, with the promotion of lower layers that have individuals with good characteristics, both in growth and quality. It is suited for stands where the irregular or low density has originated dominants of bad quality; for shade-tolerant species, as the stems in the lower layers maintain their vigour and ability to react to release and it is less suited for intolerant species, yet it can be used in young stands where trees have not lost their vigour. It should be done as earlier as possible and should be replaced by the thinning from

ii.Thinning of dominants *with permanent character*: The goal is the production of small- and medium-dimension timber. The objective is to promote canopy gaps that enhance regeneration with the largest possible number of individuals with the removal of dominant trees. When the stand is dense and uniform, this method is replaced by the thinning from below. The rotation

iii.Thinning of dominants *combined with thinning from below*: The goal is forming a superior layer with codominant individuals. It minimises the negative effects of the thinning of dominants, especially in very dense unthinned stands. Its main disadvantage is the tendency to increase the losses due to

*Mechanical* or *geometric thinning* is associated to large spacing silviculture with selected material, in which the removal of a tree is more related with its location than with its position, because the goal is to maintain a regular cover. It is advantageous in young, very dense unthinned stands. Two subtypes can be identified: *spacing*, where the trees at a certain distance of the selected tree are removed; and

*row* or *strip*, where the individuals of one or several lines are removed [6]. *Free thinning* goal is the selection of a set of trees which are maintained in free growth until the end of the rotation in order to produce high quantity of timber with high quality [22]. It is directed to oak species and rotations of less than 100 years. It begins with the selection of the future trees with a density of 60–80 trees ha−1, uniformly spaced. It is followed by the removal of all the trees whose crown distance from a future tree is less than 25% of the mean crown width (assumption to be maintained throughout rotation, to keep future trees in free growth). As a secondary silvicultural practice, pruning is recommended up to a height of 6 m as well as removing the epicormic branches [22, 23]. It has also

below as soon as the trees reach the superior layer.

length is considerably shortened.

biotic and abiotic disturbances.

**44**

been used in mixtures of conifers and oaks, and oaks in pure or mixed stands with *Fraxinus excelsior*, *Acer pseudoplatanus* and *Prunus avium* [24].

*Compensation thinning's* (*éclairci de ratrapage*) aim is favouring the future trees that have sufficient stability and well-balanced crowns, being less important in their spatial distribution and their optimal distance. It is frequently linked with the goal of keeping stand stability and should have light intensity. It is preferred in stands without or with thinnings of low intensity in the past. In these cases, only the dominant stems are able to react to release, and thus codominant individuals should be preferably removed. It is especially suited for stands in steep slope areas where it is easy to overestimate distances due to crown overlapping and asymmetry [7].

*Crown releasing thinning's* (*éclairci misse en lumiére*) main goal is regulating future trees in old growth development stage. The trees' metabolism and growth, capacity of reaction to release and ability to redo their crowns are lower than in the mature ones. The social positions are nearly definite, and the probability of individuals of the inferior social classes to ascend to upper classes is low. Future trees are released from competition from those of the intermediate layers as the dominant competitors were removed in the former thinnings. The objective is to maintain or increase diameter growth, to allow the largest possible increase of productivity in value. The intensity should be light and periodicity should be long, according to the trees' growth rates [7].

*Variable density thinning's* goal is to promote variability and heterogeneity, both spatial (horizontal and vertical) and structural [25–28], as well as stimulate latesuccessional forest structures, reduce stand density, alter species composition [25, 26, 29] and be a restauration tool [27, 30, 31]. It assumes the unevenly removal of trees, creating gradients of density in the stand. This is implemented with the creation of patches with variable spatial distribution, where canopy gaps and patches of different densities coexist [26, 27, 32]. The proportion of each patch type is also variable according to the intended complexity of stand structure, the existing stand structure, the species composition and spatial arrangement [31, 32]. Six protocols are referred, which due to their similarities were grouped in four types [32]:


Thinning *intensity* or *degree* is more frequently evaluated by the number of trees or basal area, as function of the amount of removed in relation of the total number of stems ( <sup>=</sup> *Nrem RN Nt* , where Nrem is the number of removed trees, and Nt is the total number of trees) or basal area ( <sup>=</sup> *Grem RG Gt* , where Grem is the basal area

removed, and Gt is the total basal area). It is frequently grouped in three classes: light, moderate and heavy. The most consensual ranges for light intensity are ≤25% of the number of trees and <20% of the basal area, for moderate 50% of the number of trees and 20–35% of the basal area and for heavy >50% of the number of trees and >35% of the basal area [33, 34].

#### **4. Thinning effects**

The main goals of thinning are to improve residual trees' efficiency, encompassing to concentrate growth on a selected subset of trees, thus controlling density and reallocating the growing space and reducing competition among trees while promoting their growth [35–39]. It is also considered as a mean of capturing tree mortality, providing early financial return, increasing future merchantable volume and financial value of timber [39–41]. Moreover, density threshold (or thinning intensity) enables to keep volume growth [42], which depends too on the species, stand development stage and site [41, 43, 44]. The thinning effects will be discussed for density, stand structure, stability, mortality and growth stagnation, growth, wood, biomass and carbon stocks, soil and understorey and as an adaptive measure.

Regardless of the method and intensity of thinning, *density* decreases always. All thinning methods increase individual tree growth due to the increase in growing space and reduction of competition [45–48], especially in the long term [47]. The method affects differently tree interactions post thinning. In the thinning from below, the interactions in the upper layer are maintained [7, 49], while in the thinning from above, compensation and crown releasing thinning are reduced [7, 34, 50]. In the thinning of dominants, there is a change in the interactions in the intermediate layer, which is a consequence of the removal of the upper layer [6, 51, 52]. In the free and mechanical thinnings, the spatial pattern of interactions is kept [6, 22, 23]. In the Schädelin and variable density thinnings, future trees are released from competition, resulting in the alteration of the spatial patterns of interaction, both horizontal and vertical [7, 32].

In general, the heavier the thinning intensity, the higher the decrease of density and the lower the competition. This derives in different growth reactions post thinning, which is also related to stand development stage and site quality, with growth rates increasing with thinning intensity and site quality and decreasing from initial to old growth development stages [41, 43, 50, 53].

*Stand structure* is affected by thinning, producing more or less accentuated changes depending on its method and intensity. This changes with the increase of light, water and nutrients levels (e.g*.* [54, 55]). These alterations can be observed in the diameter and height distributions, canopy stratification and spatial arrangements of trees. Thinning from below and of dominants narrow the range of diameter and height distributions and decrease canopy stratification due to the preferential removal of trees with smaller and larger dimensions, respectively [52]. Thinning from above and of Schädelin keep the range of diameter and height distributions and maintain or increase canopy stratification [20, 39, 52, 56, 57]. Compensation and crown releasing, free and mechanical thinnings tend to keep diameter and height distribution ranges and canopy stratification [6, 7, 23]. Variable density thinning increases diameter and height distribution ranges and maintains

**47**

*Thinning: An Overview*

maintain stability [7].

*DOI: http://dx.doi.org/10.5772/intechopen.93436*

uniform distances or in clusters [20].

or increases canopy stratification [29, 58–60]. The tree spatial arrangements after thinning depend on those prior to thinning. A regular spacing was reported for thinnings from below, while from above and of dominants have been referred as a trend towards cluster one at low and intermediate distances [52]. Schädelin thinning tends to derive in a uniform or cluster distribution when future trees are at

*Stand stability* depends on individual tree morphology and their spatial arrangement. It is frequently evaluated by diameter at breast height, total height, *hd* ratio (defined as quotient between total height and diameter at breast height, with both variables in the same units), stem taper, crown dimensions, crown eccentricity and crown inclination as well as root architecture [61–63]. For the same diameter at breast height, the taller the total height, the higher the *hd* ratio and the lower the stability. The increase of stability can be achieved with thinning, as it promotes diameter growth, the *hd* ratio reduction and stem taper increase [21, 61, 63]. The crown dimensions (width and length), eccentricity and inclination depend on stand structure and species traits, which are determined primordially by the amount of light. The higher the light level and the wider the spacing, the higher crown volume, and the higher the shade tolerance, the higher the crown dimensions. The constellation of neighbours reducing or promoting irregular available aerial space can promote the development of eccentric crowns and stem inclination and thus reducing stability [64, 65]. Stability is attained more efficiently with thinnings at younger ages as it enables a more favourable above- and below-ground morphology [21, 66]. Also, heavy thinnings promote tree morphologies that are more stable than moderate or light ones [21, 41, 66]. Thinnings from below increase stability by the removal of trees with the less suited morphologies (e.g*.* higher *hd* ratio), and increase with the increase of intensity due to the reduction of *hd* ratio and increase of stem taper [37, 67, 68] and crown length and crown ratio (the coefficient between crown length and total height) [69, 70]. Thinnings from above and of dominants removing trees from the upper layer may decrease stability, especially when associated to trees with high *hd* ratio and due to unbalance of aerial/root systems, eccentric crowns and the swaying of trees [35, 52, 71]. Schädelin, variable density and free thinning maintain or improve stability of thinning as the trees more stable are selected [20, 22, 32, 72]. Compensation and crown release thinning

*Mortality* after thinning can be caused by increased tree swaying due to wind or snow [71, 73] or is associated to shallow root systems' water stress [35, 36]. In general, it is higher in the thinning from above and of dominants than from below [52] or Schädelin [72]. *Growth stagnation* [74] is linked to the reduction of growth

The thinning effects on *growth* are related to a suite of factors such as method and intensity, age, species traits, density (cf. density section), stand structure

In general, thinning increases growing space and favours certain classes of trees. This results in asymmetric competition [80, 81], that is, the share of resources used by larger trees is disproportionally larger than those used by smaller trees, resulting in the growth suppression of the latter [35, 80]. Thus the increase in growth at tree level is maintained or enhanced by the methods where release occurs in the upper layers and/or favours future trees (from above, Schädelin, free, compensation, crown release or variable density thinnings) [7, 20, 23, 30, 31, 39, 59, 60, 82, 83]. This is especially true if the thinning is carried out before canopy closure and crown recession [47]. It can be explained by two factors: the available growing space and the individual tree growth strategies. In closed canopy stands, the upper layers absorb most radiation, the taller trees cast shade on their smaller neighbours and

increment [75, 76], sometimes associated to drought events [77–79].

(cf. stand structure section) and time after thinning.

#### *Thinning: An Overview DOI: http://dx.doi.org/10.5772/intechopen.93436*

*Silviculture*

of stems ( <sup>=</sup> *Nrem RN*

**4. Thinning effects**

total number of trees) or basal area ( <sup>=</sup> *Grem RG*

to old growth development stages [41, 43, 50, 53].

*Stand structure* is affected by thinning, producing more or less accentuated changes depending on its method and intensity. This changes with the increase of light, water and nutrients levels (e.g*.* [54, 55]). These alterations can be observed in the diameter and height distributions, canopy stratification and spatial arrangements of trees. Thinning from below and of dominants narrow the range of diameter and height distributions and decrease canopy stratification due to the preferential removal of trees with smaller and larger dimensions, respectively [52]. Thinning from above and of Schädelin keep the range of diameter and height distributions and maintain or increase canopy stratification [20, 39, 52, 56, 57]. Compensation and crown releasing, free and mechanical thinnings tend to keep diameter and height distribution ranges and canopy stratification [6, 7, 23]. Variable density thinning increases diameter and height distribution ranges and maintains

and >35% of the basal area [33, 34].

Thinning *intensity* or *degree* is more frequently evaluated by the number of trees or basal area, as function of the amount of removed in relation of the total number

removed, and Gt is the total basal area). It is frequently grouped in three classes: light, moderate and heavy. The most consensual ranges for light intensity are ≤25% of the number of trees and <20% of the basal area, for moderate 50% of the number of trees and 20–35% of the basal area and for heavy >50% of the number of trees

The main goals of thinning are to improve residual trees' efficiency, encompassing to concentrate growth on a selected subset of trees, thus controlling density and reallocating the growing space and reducing competition among trees while promoting their growth [35–39]. It is also considered as a mean of capturing tree mortality, providing early financial return, increasing future merchantable volume and financial value of timber [39–41]. Moreover, density threshold (or thinning intensity) enables to keep volume growth [42], which depends too on the species, stand development stage and site [41, 43, 44]. The thinning effects will be discussed for density, stand structure, stability, mortality and growth stagnation, growth, wood, biomass and carbon stocks, soil and understorey and as an adaptive measure. Regardless of the method and intensity of thinning, *density* decreases always. All thinning methods increase individual tree growth due to the increase in growing space and reduction of competition [45–48], especially in the long term [47]. The method affects differently tree interactions post thinning. In the thinning from below, the interactions in the upper layer are maintained [7, 49], while in the thinning from above, compensation and crown releasing thinning are reduced [7, 34, 50]. In the thinning of dominants, there is a change in the interactions in the intermediate layer, which is a consequence of the removal of the upper layer [6, 51, 52]. In the free and mechanical thinnings, the spatial pattern of interactions is kept [6, 22, 23]. In the Schädelin and variable density thinnings, future trees are released from competition, resulting in the alteration of the spatial patterns of interaction, both horizontal and vertical [7, 32]. In general, the heavier the thinning intensity, the higher the decrease of density and the lower the competition. This derives in different growth reactions post thinning, which is also related to stand development stage and site quality, with growth rates increasing with thinning intensity and site quality and decreasing from initial

*Nt* , where Nrem is the number of removed trees, and Nt is the

*Gt* , where Grem is the basal area

**46**

or increases canopy stratification [29, 58–60]. The tree spatial arrangements after thinning depend on those prior to thinning. A regular spacing was reported for thinnings from below, while from above and of dominants have been referred as a trend towards cluster one at low and intermediate distances [52]. Schädelin thinning tends to derive in a uniform or cluster distribution when future trees are at uniform distances or in clusters [20].

*Stand stability* depends on individual tree morphology and their spatial arrangement. It is frequently evaluated by diameter at breast height, total height, *hd* ratio (defined as quotient between total height and diameter at breast height, with both variables in the same units), stem taper, crown dimensions, crown eccentricity and crown inclination as well as root architecture [61–63]. For the same diameter at breast height, the taller the total height, the higher the *hd* ratio and the lower the stability. The increase of stability can be achieved with thinning, as it promotes diameter growth, the *hd* ratio reduction and stem taper increase [21, 61, 63]. The crown dimensions (width and length), eccentricity and inclination depend on stand structure and species traits, which are determined primordially by the amount of light. The higher the light level and the wider the spacing, the higher crown volume, and the higher the shade tolerance, the higher the crown dimensions. The constellation of neighbours reducing or promoting irregular available aerial space can promote the development of eccentric crowns and stem inclination and thus reducing stability [64, 65]. Stability is attained more efficiently with thinnings at younger ages as it enables a more favourable above- and below-ground morphology [21, 66]. Also, heavy thinnings promote tree morphologies that are more stable than moderate or light ones [21, 41, 66]. Thinnings from below increase stability by the removal of trees with the less suited morphologies (e.g*.* higher *hd* ratio), and increase with the increase of intensity due to the reduction of *hd* ratio and increase of stem taper [37, 67, 68] and crown length and crown ratio (the coefficient between crown length and total height) [69, 70]. Thinnings from above and of dominants removing trees from the upper layer may decrease stability, especially when associated to trees with high *hd* ratio and due to unbalance of aerial/root systems, eccentric crowns and the swaying of trees [35, 52, 71]. Schädelin, variable density and free thinning maintain or improve stability of thinning as the trees more stable are selected [20, 22, 32, 72]. Compensation and crown release thinning maintain stability [7].

*Mortality* after thinning can be caused by increased tree swaying due to wind or snow [71, 73] or is associated to shallow root systems' water stress [35, 36]. In general, it is higher in the thinning from above and of dominants than from below [52] or Schädelin [72]. *Growth stagnation* [74] is linked to the reduction of growth increment [75, 76], sometimes associated to drought events [77–79].

The thinning effects on *growth* are related to a suite of factors such as method and intensity, age, species traits, density (cf. density section), stand structure (cf. stand structure section) and time after thinning.

In general, thinning increases growing space and favours certain classes of trees. This results in asymmetric competition [80, 81], that is, the share of resources used by larger trees is disproportionally larger than those used by smaller trees, resulting in the growth suppression of the latter [35, 80]. Thus the increase in growth at tree level is maintained or enhanced by the methods where release occurs in the upper layers and/or favours future trees (from above, Schädelin, free, compensation, crown release or variable density thinnings) [7, 20, 23, 30, 31, 39, 59, 60, 82, 83]. This is especially true if the thinning is carried out before canopy closure and crown recession [47]. It can be explained by two factors: the available growing space and the individual tree growth strategies. In closed canopy stands, the upper layers absorb most radiation, the taller trees cast shade on their smaller neighbours and

tree swaying may derive branch abrasion [1]. These three factors promote height growth and constrain crown lateral development [84]. In fact, it has been reported that the dominant height increases with density for broadleaved species [41, 85], due its effects on epinastic control and specificities of stand development at early ages [41]. The inverse has been reported for the conifers [86, 87].

Thinning intensity influences directly density and thus the availability of growing space for individual stems, which in turn affects height, stem and crown growth [69, 88, 89]. Growth, at tree-level basis, increases with thinning intensity [37, 50, 71, 89, 90]. In general, smaller/medium and/or younger trees react faster and with higher growth rates than larger ones [50, 75, 91]. After moderate and heavy thinnings, especially those carried out early, dominant and codominant trees have higher radial growth than supressed ones [37, 38, 67, 71, 75]. Stand age and site also curtails the response to thinning, the younger the stand and the better site quality, the larger the diameter increments [37]. Moreover, dominant trees have higher diameter growth [37] and need less time to react to release [91]. This is especially true with mature trees that have reached their maximum growth potential [35, 71]. However, a positive trend in above-ground biomass has been reported for large trees [92–94]. This trend seems to be linked with shade tolerance. Shade-intolerant species increase growth with light increase, though reaching maximum annual growth at younger ages conversely to shade-tolerant species [35, 77]. Also, according to Bose et al. [35], thinning intensity plays a less important role in growth increase after thinning in very shade-tolerant species than in shade-intolerant ones as the former are not able to use the increased growing space after thinning (especially light) efficiently.

Differences in tree reaction to thinning with age also depend on the stand history. While in unthinned stands, recovery decreased with stand age, it did not decrease in thinned stands [95], at least partially explained, by the larger crowns in thinned stands that enable a faster recovery of growth [95, 96].

After thinning, the trees increase their growth, frequently 1–3 years after thinning [50, 82] due to the availability of growing space. The growth increase derives in the increase of crown volume (width and length), crown cover [90, 97] and foliar mass enhancing photosynthetic capacity, as the lower parts of the crowns receive more light than unthinned stands [98]. As trees occupy gradually the available growing space, the growth rate decreases [35, 36, 99] after reaching the maximum (about 3 years after thinning), attaining 7–8 years after thinning, growth levels similar to the unthinned stands [50]. Primicia et al. [99] reported that magnitude and duration of thinning effects on growth (stem and crown diameter) as well as on mortality seem to be more related to thinning intensity than with thinning method.

*Wood quantity* and *quality* can be improved by thinning. In general, quantity per tree increases with thinning intensity [100], though it depends also on the species and their ecological and cultural traits. Light thinnings favour more regular growth rings, especially interesting for timber, though with overall smaller diameter growth, while heavy thinnings promote larger annual growth rings [77, 101]. The counterpart of thinning is the development of large branches that reduce the wood quality. Consequently, a compromise has to be equated between low and high densities as function of the species and its traits (e.g*.* epinastic control and natural pruning ability), associated frequently to future tree selection, pruning and early silvicultural operations [21, 37, 38, 83], especially in what regards wolf trees, which should be removed as early as possible [102].

In general, thinning reduces *biomass* and *carbon storage* when compared with unthinned stands, the decrease is higher in thinning from above and of dominants [39, 103] than from below [104, 105]. Yet, the effects of thinning are dependent also on the individual tree development stage, their growth rates and density after

**49**

variable density thinnings.

*Thinning: An Overview*

*DOI: http://dx.doi.org/10.5772/intechopen.93436*

with early thinning from below [41].

thinning [106, 107]. In the short term, thinning of young trees results in a reduction of above-ground carbon even if there is an increase of the individual tree's growth rate, because they are not able to use all the growing space available, that is, they do not fully occupy the site [104, 108]. In general, increasing thinning intensities result in decreasing standing and deadwood biomass and literfall [109, 110]. At stand level, it seems that biomass and carbon storage is the result of the interaction between the density and size of the overstorey trees. Though with an inverse relationship, they balance each other, resulting in a rather constant above-ground carbon stock, regardless of whether stands are thinned or not [39, 41], especially

*Soil* and *understory* vegetations are affected by thinning. If biomass residues are kept in the stand, their decomposition incorporates carbon in the soil. Thinning increasing decomposition rates decreases the soil carbon stocks. In the 0–10 cm of the soil layer, carbon stock is higher than in the 10–20 cm layer [39, 40], due to higher decomposition rates [111]. Yet, with time and tree growth, soil carbon stocks tend to be similar in thinned and unthinned stands [112]. Zhang et al. [39] reported that soil carbon stocks prior and 5 years after thinning were similar. Thinnings originate higher light levels in the lower storeys, which can result in higher transpiration and water loss by evaporation (e.g*.* [54, 55]) and increase of the understorey vegetation, the higher the thinning intensity [39]. This is particularly negative if it is composed mainly by shrub vegetation [39]. Yet, heavy thinnings favour pasture

Thinnings are considered primordial adaptive measures as they can reduce

Thinning can reduce vulnerability to climate change [95] as it controls stand density [41]. It can improve tree and stand growth by releasing growing space (e.g*.* [41, 77, 114]), including increasing water availability and their use efficiency [77, 101], thus mitigating the effects of the droughts (i.e. water deficits) [77, 95, 114, 115]. Fire prevention is enhanced by thinnings (including also pruning) as they reduce the quantity and horizontal and vertical continuity of fuel, [116] enabling stands to withstand surface fires [117] and increase the canopy seed bank storage [118]. Thinning intensity has a primordial effect on the magnitude and duration of the drought effects on trees and stands. The higher the proportion of crown cover removed, the longer the effects of thinning, that is, more water reaches the soil, enabling drought effects' mitigation [95, 101, 119]. Less-intensive thinnings reach prethinning transpiration levels in a few years, [55, 114] while in heavy ones they last longer [119], occasioning tree growth rates' increase [95, 101, 120]. Broadleaved species seem to have developed resistance mechanisms, mitigating diameter growth reduction [121]. This can be due to the deeper root systems [122] and spring radial growth (especially in the ring-porous species) is much larger than in the autumn one [123]. Conifers seem to have improved recovery and resilience mechanisms, probably due to more precipitation reaching the soil and transpiration reduction [95, 121]. Regardless of tree species, the stronger the drought severity, the longer the recovery period in diameter growth [95], which is probably related to the longer period needed to restore the soil water and to rebuild fine root system [124]. Thus, species with higher expansion rates, increase of leaf area (assimilation ability) and fine roots (water absorption

production, a suitable option for agroforestry systems [90, 113].

vulnerability to climate change, fires, droughts and increase diversity.

ability), are expected to have more benefits from thinning [115, 125].

An increased diversity in stand structure, especially in pure even-aged stands, particularly in plantations, can be derived from thinning in tree' dimensions [126] and/or their variability [20, 39, 52, 57] as well as in species and their proportions [127] and produces greater trade-offs with other ecosystem services [128, 129]. This is especially valid with methods that promote variability, such as Schädelin or

#### *Thinning: An Overview DOI: http://dx.doi.org/10.5772/intechopen.93436*

*Silviculture*

light) efficiently.

tree swaying may derive branch abrasion [1]. These three factors promote height growth and constrain crown lateral development [84]. In fact, it has been reported that the dominant height increases with density for broadleaved species [41, 85], due its effects on epinastic control and specificities of stand development at early

Thinning intensity influences directly density and thus the availability of growing space for individual stems, which in turn affects height, stem and crown growth [69, 88, 89]. Growth, at tree-level basis, increases with thinning intensity [37, 50, 71, 89, 90]. In general, smaller/medium and/or younger trees react faster and with higher growth rates than larger ones [50, 75, 91]. After moderate and heavy thinnings, especially those carried out early, dominant and codominant trees have higher radial growth than supressed ones [37, 38, 67, 71, 75]. Stand age and site also curtails the response to thinning, the younger the stand and the better site quality, the larger the diameter increments [37]. Moreover, dominant trees have higher diameter growth [37] and need less time to react to release [91]. This is especially true with mature trees that have reached their maximum growth potential [35, 71]. However, a positive trend in above-ground biomass has been reported for large trees [92–94]. This trend seems to be linked with shade tolerance. Shade-intolerant species increase growth with light increase, though reaching maximum annual growth at younger ages conversely to shade-tolerant species [35, 77]. Also, according to Bose et al. [35], thinning intensity plays a less important role in growth increase after thinning in very shade-tolerant species than in shade-intolerant ones as the former are not able to use the increased growing space after thinning (especially

Differences in tree reaction to thinning with age also depend on the stand history. While in unthinned stands, recovery decreased with stand age, it did not decrease in thinned stands [95], at least partially explained, by the larger crowns in

After thinning, the trees increase their growth, frequently 1–3 years after thinning [50, 82] due to the availability of growing space. The growth increase derives in the increase of crown volume (width and length), crown cover [90, 97] and foliar mass enhancing photosynthetic capacity, as the lower parts of the crowns receive more light than unthinned stands [98]. As trees occupy gradually the available growing space, the growth rate decreases [35, 36, 99] after reaching the maximum (about 3 years after thinning), attaining 7–8 years after thinning, growth levels similar to the unthinned stands [50]. Primicia et al. [99] reported that magnitude and duration of thinning effects on growth (stem and crown diameter) as well as on mortality seem to be more related to thinning intensity than with thinning method. *Wood quantity* and *quality* can be improved by thinning. In general, quantity per tree increases with thinning intensity [100], though it depends also on the species and their ecological and cultural traits. Light thinnings favour more regular growth rings, especially interesting for timber, though with overall smaller diameter growth, while heavy thinnings promote larger annual growth rings [77, 101]. The counterpart of thinning is the development of large branches that reduce the wood quality. Consequently, a compromise has to be equated between low and high densities as function of the species and its traits (e.g*.* epinastic control and natural pruning ability), associated frequently to future tree selection, pruning and early silvicultural operations [21, 37, 38, 83], especially in what regards wolf trees, which

In general, thinning reduces *biomass* and *carbon storage* when compared with unthinned stands, the decrease is higher in thinning from above and of dominants [39, 103] than from below [104, 105]. Yet, the effects of thinning are dependent also on the individual tree development stage, their growth rates and density after

thinned stands that enable a faster recovery of growth [95, 96].

should be removed as early as possible [102].

ages [41]. The inverse has been reported for the conifers [86, 87].

**48**

thinning [106, 107]. In the short term, thinning of young trees results in a reduction of above-ground carbon even if there is an increase of the individual tree's growth rate, because they are not able to use all the growing space available, that is, they do not fully occupy the site [104, 108]. In general, increasing thinning intensities result in decreasing standing and deadwood biomass and literfall [109, 110]. At stand level, it seems that biomass and carbon storage is the result of the interaction between the density and size of the overstorey trees. Though with an inverse relationship, they balance each other, resulting in a rather constant above-ground carbon stock, regardless of whether stands are thinned or not [39, 41], especially with early thinning from below [41].

*Soil* and *understory* vegetations are affected by thinning. If biomass residues are kept in the stand, their decomposition incorporates carbon in the soil. Thinning increasing decomposition rates decreases the soil carbon stocks. In the 0–10 cm of the soil layer, carbon stock is higher than in the 10–20 cm layer [39, 40], due to higher decomposition rates [111]. Yet, with time and tree growth, soil carbon stocks tend to be similar in thinned and unthinned stands [112]. Zhang et al. [39] reported that soil carbon stocks prior and 5 years after thinning were similar. Thinnings originate higher light levels in the lower storeys, which can result in higher transpiration and water loss by evaporation (e.g*.* [54, 55]) and increase of the understorey vegetation, the higher the thinning intensity [39]. This is particularly negative if it is composed mainly by shrub vegetation [39]. Yet, heavy thinnings favour pasture production, a suitable option for agroforestry systems [90, 113].

Thinnings are considered primordial adaptive measures as they can reduce vulnerability to climate change, fires, droughts and increase diversity.

Thinning can reduce vulnerability to climate change [95] as it controls stand density [41]. It can improve tree and stand growth by releasing growing space (e.g*.* [41, 77, 114]), including increasing water availability and their use efficiency [77, 101], thus mitigating the effects of the droughts (i.e. water deficits) [77, 95, 114, 115].

Fire prevention is enhanced by thinnings (including also pruning) as they reduce the quantity and horizontal and vertical continuity of fuel, [116] enabling stands to withstand surface fires [117] and increase the canopy seed bank storage [118].

Thinning intensity has a primordial effect on the magnitude and duration of the drought effects on trees and stands. The higher the proportion of crown cover removed, the longer the effects of thinning, that is, more water reaches the soil, enabling drought effects' mitigation [95, 101, 119]. Less-intensive thinnings reach prethinning transpiration levels in a few years, [55, 114] while in heavy ones they last longer [119], occasioning tree growth rates' increase [95, 101, 120]. Broadleaved species seem to have developed resistance mechanisms, mitigating diameter growth reduction [121]. This can be due to the deeper root systems [122] and spring radial growth (especially in the ring-porous species) is much larger than in the autumn one [123]. Conifers seem to have improved recovery and resilience mechanisms, probably due to more precipitation reaching the soil and transpiration reduction [95, 121]. Regardless of tree species, the stronger the drought severity, the longer the recovery period in diameter growth [95], which is probably related to the longer period needed to restore the soil water and to rebuild fine root system [124]. Thus, species with higher expansion rates, increase of leaf area (assimilation ability) and fine roots (water absorption ability), are expected to have more benefits from thinning [115, 125].

An increased diversity in stand structure, especially in pure even-aged stands, particularly in plantations, can be derived from thinning in tree' dimensions [126] and/or their variability [20, 39, 52, 57] as well as in species and their proportions [127] and produces greater trade-offs with other ecosystem services [128, 129]. This is especially valid with methods that promote variability, such as Schädelin or variable density thinnings.

#### **5. Conclusion**

Stand structure and production goals influence the thinning method and its intensity, which in turn affects stand structure and the quantity and quality of the products. Thus, it is of primordial importance the selection of the most suitable methods (that can be more than one during the production cycle) as well as their intensities (which can vary too along the production cycle) that have also to be suited to the products and services desired to the forest stand. Thinning is frequently linked to tree selection. Tree classification systems are quick, low-cost tools that enable thinning implementation and are also a monitoring tool that enables the evaluation of the dynamics of the forest stands.

All thinnings reduce density, however, their effects on density, stand structure, growth, soil, understorey vegetation and diversity depend on the method and intensity of thinning, stand development stage and site quality. The positive effects of thinning are the increase in growth and production, especially in value, and the reduction of the vulnerability of the forest systems to climate change, droughts and fire. The negative effects are related to the reaction of the trees to release, which can cause mortality, growth stagnation or no increase of the growth rates.

#### **Acknowledgements**

This work is funded by National Funds through FCT–Foundation for Science and Technology, under the Project UIDB/05183/2020 (MED) and Project UID/ EMS/50022/2019 (through IDMEC, under LAETA).

#### **Author details**

Ana Cristina Gonçalves Department of Rural Engineering, School of Sciences and Technology, MED-Mediterranean Institute for Agriculture, Environment and Development, Institute of Research and Advanced Education (IIFA), University of Évora, Évora, Portugal

\*Address all correspondence to: acag@uevora.pt

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**51**

*Thinning: An Overview*

**References**

pp. 506

pp. 468

1989. pp. 284

Inc.; 1997. pp. 560

Romandes; 1990. pp. 245

Publishing; 1996. pp. 413

Press; 2014. pp. 213

2009. pp. 664

[8] Florence RG. Ecology and

*DOI: http://dx.doi.org/10.5772/intechopen.93436*

[1] Oliver CD, Larson BC. Forest Stand Dynamics. Update ed. New York: John Wiley & Sons, Inc; 1996. pp. 544

[12] Kerr G, Haufe J. Thinning Practice—A Silvicultural Guide.

[13] Meadows JS, Burkhardt EC, Johnson RL, Hodges JD. A numerical rating system for crown classes of southern hardwoods. Southern Journal of Applied Forestry. 2001;**25**:154-158

1993. pp. 58 (NA-TP-19-93)

[15] Gonçalves AC. Modelação de povoamentos adultos de pinheiro bravo com regeneração de folhosas na Serra da Lousã. Lisboa: Instituto Superior de Agronomia, Universidade Técnica de

[16] Gonçalves AC. Estabelecimento de ensaios para avaliação do efeito do primeiro desbaste no desenvolvimento

[17] Oswald H. Résultats principaux des places déxpérience de chêne du centre national de recherches forestières. Revue Forestière Française. 1981;**XXXIII**

[18] Polge H. Prodution de chênes de qualité. Revue Forestiére Francaise.

[20] Boncina A. Comparison of structure and biodiversity in the Rajhenav virgin forest remnant and managed forest in the Dinaric region of Slovenia. Global Ecology and Biogeography.

[21] Cameron AD. Importance of early selective thinning in the development of

[19] Roy FX. La désignation des arbres de place dans les futaies de chêne destinées à fournir du bois de tranchage. Revue Forestiére Francaise.

de montados de sobro. 1996

[14] Perkey AW, Wilkins BL, Smith HC. Crop Tree Management in Eastern Hardwoods. USDA, Forest Service;

2011. p. 54

Lisboa; 2003

(no sp):65-85

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1975;**XXVII**(1):50-60

2000;**9**(3):201-211

[2] Assmann E. The Principles of Forest Yield Study. Pergamon Press; 1970.

[3] Boudru M. Forêt et Sylviculture. Le Traitement des Forêts. Vol. Tome 2. Gembloux: Presses Agronomiques de

[4] Lanier L, Badré M, Delabraze P, Dubourdieu J, Flammarion JP. Précis de Sylviculture. Engref: Nancy; 1986.

[5] Matthews JD. Silvicultural Systems. Oxford: Claredon Press;

[6] Smith DM, Larson BC, Kelty MJ, Ashton PMS. The Practice of

Silviculture. Applied Forest Ecology. 9th ed. New York: John Wiley & Sons,

[7] Schütz JP. Sylviculture 1. Principes d'Éducation des Forêts. Lausanne: Presses Polytechniques et Universitaires

Silviculture of Eucalyptus Forests. Csiro

[9] O'Hara KL. Multiaged Silviculture Managing for Complex Forest Stand Structures. Oxford: Oxford University

[10] Pretzsch H. Forest dynamics, growth, and yield. Berlin: Springer;

[11] Meadows JS, Skojac DAA. New tree classification system for Southern Hardwoods. Southern Journal of Applied Forestry. 2008;**32**(2):69-79

Gembloux; 1989. pp. 344

### **References**

*Silviculture*

**5. Conclusion**

**50**

**Author details**

Portugal

Ana Cristina Gonçalves

**Acknowledgements**

Department of Rural Engineering, School of Sciences and Technology,

\*Address all correspondence to: acag@uevora.pt

provided the original work is properly cited.

evaluation of the dynamics of the forest stands.

EMS/50022/2019 (through IDMEC, under LAETA).

MED-Mediterranean Institute for Agriculture, Environment and Development, Institute of Research and Advanced Education (IIFA), University of Évora, Évora,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Stand structure and production goals influence the thinning method and its intensity, which in turn affects stand structure and the quantity and quality of the products. Thus, it is of primordial importance the selection of the most suitable methods (that can be more than one during the production cycle) as well as their intensities (which can vary too along the production cycle) that have also to be suited to the products and services desired to the forest stand. Thinning is frequently linked to tree selection. Tree classification systems are quick, low-cost tools that enable thinning implementation and are also a monitoring tool that enables the

All thinnings reduce density, however, their effects on density, stand structure,

This work is funded by National Funds through FCT–Foundation for Science and Technology, under the Project UIDB/05183/2020 (MED) and Project UID/

growth, soil, understorey vegetation and diversity depend on the method and intensity of thinning, stand development stage and site quality. The positive effects of thinning are the increase in growth and production, especially in value, and the reduction of the vulnerability of the forest systems to climate change, droughts and fire. The negative effects are related to the reaction of the trees to release, which can

cause mortality, growth stagnation or no increase of the growth rates.

[1] Oliver CD, Larson BC. Forest Stand Dynamics. Update ed. New York: John Wiley & Sons, Inc; 1996. pp. 544

[2] Assmann E. The Principles of Forest Yield Study. Pergamon Press; 1970. pp. 506

[3] Boudru M. Forêt et Sylviculture. Le Traitement des Forêts. Vol. Tome 2. Gembloux: Presses Agronomiques de Gembloux; 1989. pp. 344

[4] Lanier L, Badré M, Delabraze P, Dubourdieu J, Flammarion JP. Précis de Sylviculture. Engref: Nancy; 1986. pp. 468

[5] Matthews JD. Silvicultural Systems. Oxford: Claredon Press; 1989. pp. 284

[6] Smith DM, Larson BC, Kelty MJ, Ashton PMS. The Practice of Silviculture. Applied Forest Ecology. 9th ed. New York: John Wiley & Sons, Inc.; 1997. pp. 560

[7] Schütz JP. Sylviculture 1. Principes d'Éducation des Forêts. Lausanne: Presses Polytechniques et Universitaires Romandes; 1990. pp. 245

[8] Florence RG. Ecology and Silviculture of Eucalyptus Forests. Csiro Publishing; 1996. pp. 413

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[21] Cameron AD. Importance of early selective thinning in the development of long-term stand stability and improved log quality: A review. Forestry. 2002;**75**(1):25-35

[22] Jobling J, Pearce ML. Free-growth of oak. Forest Record. 1977;**113**:3-17

[23] Kerr G. The effect of heavy or "free growth" thinning on oak (*Quercus petraea* and *Q. robur*). Forestry. 1996;**69**(4):303-317

[24] Kerr G, Evans J. Growing broadleaves for timber. In: Forestry Commission Handbook. London: H.M.S.O; 1993. pp. 95

[25] Carey AB. Active and passive forest management for multiple values. Northwestern Naturalist. 2006;**87**(1):18

[26] Carey AB. Biocomplexity and restoration of biodiversity in temperate coniferous forest: Inducing spatial heterogeneity with variable-density thinning. Forestry. 2003;**76**(2):127-136

[27] Comfort EJ, Roberts SD, Harrington CA. Midcanopy growth following thinning in young-growth conifer forests on the Olympic Peninsula western Washington. Forest Ecology and Management. 2010;**259**(8):1606-1614

[28] Sullivan TP, Sullivan DS, Lindgren PMF, Ransome DB. Stand structure and small mammals in intensively managed forests: Scale, time, and testing extremes. Forest Ecology and Management. 2013;**310**:1071-1087

[29] Puettmann K, Ares A, Burton J, Dodson E. Forest restoration using variable density thinning: Lessons from Douglas-Fir stands in Western Oregon. Forests. 2016;**7**(12):310

[30] O'Hara KL, Nesmith JCB, Leonard L, Porter DJ. Restoration of old forest features in Coast Redwood Forests using early-stage variabledensity thinning. Restororation Ecology. 2010;**18**:125-135

[31] Roberts SD, Harrington CA. Individual tree growth response to variable-density thinning in coastal Pacific Northwest forests. Forest Ecology and Management. 2008;**255**(7):2771-2781

[32] O'Hara KL, Leonard LP, Keyes CR. Variable-density thinning and a marking paradox: Comparing prescription protocols to attain stand variability in Coast Redwood. Western Journal of Applied Forestry. 2012;**27**(3):143-149

[33] del Río M, Bravo-Oviedo A, Pretzsch H, Löf M, Ruiz-Peinado R. A review of thinning effects on Scots pine stands: From growth and yield to new challenges under global change. Forest Systems. 2017;**26**(2):eR03S

[34] Gradel A, Ammer C, Ganbaatar B, Nadaldorj O, Dovdondemberel B, Wagner S. On the effect of thinning on tree growth and stand structure of White Birch (*Betula platyphylla* Sukaczev) and Siberian Larch (*Larix sibirica* Ledeb.) in Mongolia. Forests. 2017;**8**(4):105

[35] Bose AK, Weiskittel A, Kuehne C, Wagner RG, Turnblom E, Burkhart HE. Does commercial thinning improve stand-level growth of the three most commercially important softwood forest types in North America? Forest Ecology and Management. 2018;**409**:683-693

[36] Kuehne C, Weiskittel AR, Wagner RG, Roth BE. Development and evaluation of individual tree- and stand-level approaches for predicting spruce-fir response to commercial thinning in Maine, USA. Forest Ecology and Management. 2016;**376**:84-95

[37] Mäkinen H, Isomäki A. Thinning intensity and long-term changes in increment and stem form of Scots pine trees. Forest Ecology and Management. 2004;**203**(1-3):21-34

**53**

*Thinning: An Overview*

2019;**138**(3):433-443

2015;**134**(5):737-754

2019;**433**:276-286

2016;**210**(1):108-121

*DOI: http://dx.doi.org/10.5772/intechopen.93436*

[38] Peltola H, Kilpeläinen A, Sauvala K, Räisänen T, Ikonen V-P. Effects of early thinning regime and tree status on the radial growth and wood density of Scots pine. Silva Fennica. 2007;**41**(3):489-505

[46] Hoover C, Stout S. The carbon consequences of thinning techniques: Stand structure makes a difference. Journal of Forestry. 2007;**105**(5):

[47] Horner GJ, Baker PJ, Nally RM, Cunningham SC, Thomson JR, Hamilton F. Forest structure, habitat and carbon benefits from thinning floodplain forests: Managing early stand density makes a difference. Forest Ecology and Management.

266-270

2010;**259**(3):286-293

[48] Schaedel MS, Larson AJ,

Affleck DLR, Belote RT, Goodburn JM, Page-Dumroese DS. Early forest thinning changes aboveground carbon distribution among pools, but not total amount. Forest Ecology and Management. 2017;**389**:187-198

[49] Lei X, Lu Y, Peng C, Zhang X, Chang J, Hong L. Growth and structure development of semi-natural larchspruce-fir (*Larix olgensis*–*Picea jezoensis*–*Abies nephrolepis*) forests in northeast China: 12-year results after thinning. Forest Ecology and Management. 2007;**240**(1-3):165-177

[50] Juodvalkis A, Kairiukstis L, Vasiliauskas R. Effects of thinning on growth of six tree species in north-temperate forests of Lithuania. European Journal of Forest Research.

[51] Bradford JB, Palik BJ. A comparison of thinning methods in red pine: Consequences for stand-level growth and tree diameter. Canadian Journal of Forest Research. 2009;**39**(3):489-496

2005;**124**(3):187-192

[52] Kuehne C, Weiskittel A, Pommerening A, Wagner RG. Evaluation of 10-year temporal and spatial variability in structure and growth across contrasting commercial thinning treatments in spruce-fir forests of northern Maine, USA. Annals of Forest Science. 2018;**75**(1):20

[39] Zhang H, Zhou G, Wang Y, Bai S, Sun Z, Berninger F, et al. Thinning and species mixing in Chinese fir monocultures improve carbon sequestration in subtropical China. European Journal of Forest Research.

[40] Strukelj M, Brais S, Paré D. Nineyear changes in carbon dynamics following different intensities of harvesting in boreal aspen stands. European Journal of Forest Research.

[41] Trouvé R, Bontemps J-D, Collet C, Seynave I, Lebourgeois F. When do dendrometric rules fail? Insights from 20 years of experimental thinnings on sessile oak in the GIS Coop network. Forest Ecology and Management.

[42] Zeide B. Thinning and growth. Journal of Forestry. 2001:20-25

[43] Giuggiola A, Ogée J, Rigling A, Gessler A, Bugmann H, Treydte K. Improvement of water and light availability after thinning at a xeric site: Which matters more? A dual isotope approach. New Phytologist.

[44] Taeger S, Zang C, Liesebach M, Schneck V, Menzel A. Impact of climate and drought events on the growth of Scots pine (*Pinus sylvestris* L.) provenances. Forest Ecology and Management. 2013;**307**:30-42

[45] Dwyer JM, Fensham R, Buckley YM. Restoration thinning accelerates structural development and carbon sequestration in an endangered Australian ecosystem: Restoration thinning in natural regrowth. Journal of Applied Ecology. 2010;**47**(3):681-691

#### *Thinning: An Overview DOI: http://dx.doi.org/10.5772/intechopen.93436*

*Silviculture*

2002;**75**(1):25-35

1996;**69**(4):303-317

H.M.S.O; 1993. pp. 95

long-term stand stability and improved

[31] Roberts SD, Harrington CA. Individual tree growth response to variable-density thinning in coastal Pacific Northwest forests. Forest Ecology and Management.

2008;**255**(7):2771-2781

2012;**27**(3):143-149

[32] O'Hara KL, Leonard LP,

Keyes CR. Variable-density thinning and a marking paradox: Comparing prescription protocols to attain stand variability in Coast Redwood. Western Journal of Applied Forestry.

[33] del Río M, Bravo-Oviedo A, Pretzsch H, Löf M, Ruiz-Peinado R. A review of thinning effects on Scots pine stands: From growth and yield to new challenges under global change. Forest

Systems. 2017;**26**(2):eR03S

2017;**8**(4):105

2018;**409**:683-693

2004;**203**(1-3):21-34

[36] Kuehne C, Weiskittel AR, Wagner RG, Roth BE. Development and evaluation of individual tree- and stand-level approaches for predicting spruce-fir response to commercial thinning in Maine, USA. Forest Ecology and Management. 2016;**376**:84-95

[37] Mäkinen H, Isomäki A. Thinning intensity and long-term changes in increment and stem form of Scots pine trees. Forest Ecology and Management.

[34] Gradel A, Ammer C, Ganbaatar B, Nadaldorj O, Dovdondemberel B, Wagner S. On the effect of thinning on tree growth and stand structure of White Birch (*Betula platyphylla* Sukaczev) and Siberian Larch (*Larix sibirica* Ledeb.) in Mongolia. Forests.

[35] Bose AK, Weiskittel A, Kuehne C, Wagner RG, Turnblom E, Burkhart HE. Does commercial thinning improve stand-level growth of the three most commercially important softwood forest types in North America? Forest Ecology and Management.

[22] Jobling J, Pearce ML. Free-growth of

[23] Kerr G. The effect of heavy or "free growth" thinning on oak (*Quercus petraea* and *Q. robur*). Forestry.

log quality: A review. Forestry.

oak. Forest Record. 1977;**113**:3-17

[24] Kerr G, Evans J. Growing broadleaves for timber. In: Forestry Commission Handbook. London:

[25] Carey AB. Active and passive forest management for multiple values. Northwestern Naturalist. 2006;**87**(1):18

[26] Carey AB. Biocomplexity and restoration of biodiversity in temperate coniferous forest: Inducing spatial heterogeneity with variable-density thinning. Forestry. 2003;**76**(2):127-136

[27] Comfort EJ, Roberts SD, Harrington CA. Midcanopy growth following thinning in young-growth conifer forests on the Olympic Peninsula western Washington. Forest Ecology and Management. 2010;**259**(8):1606-1614

[28] Sullivan TP, Sullivan DS, Lindgren PMF, Ransome DB. Stand structure and small mammals in

intensively managed forests: Scale, time, and testing extremes. Forest Ecology and Management. 2013;**310**:1071-1087

[29] Puettmann K, Ares A, Burton J, Dodson E. Forest restoration using variable density thinning: Lessons from Douglas-Fir stands in Western Oregon.

Forests. 2016;**7**(12):310

2010;**18**:125-135

[30] O'Hara KL, Nesmith JCB, Leonard L, Porter DJ. Restoration of old forest features in Coast Redwood Forests using early-stage variabledensity thinning. Restororation Ecology.

**52**

[38] Peltola H, Kilpeläinen A, Sauvala K, Räisänen T, Ikonen V-P. Effects of early thinning regime and tree status on the radial growth and wood density of Scots pine. Silva Fennica. 2007;**41**(3):489-505

[39] Zhang H, Zhou G, Wang Y, Bai S, Sun Z, Berninger F, et al. Thinning and species mixing in Chinese fir monocultures improve carbon sequestration in subtropical China. European Journal of Forest Research. 2019;**138**(3):433-443

[40] Strukelj M, Brais S, Paré D. Nineyear changes in carbon dynamics following different intensities of harvesting in boreal aspen stands. European Journal of Forest Research. 2015;**134**(5):737-754

[41] Trouvé R, Bontemps J-D, Collet C, Seynave I, Lebourgeois F. When do dendrometric rules fail? Insights from 20 years of experimental thinnings on sessile oak in the GIS Coop network. Forest Ecology and Management. 2019;**433**:276-286

[42] Zeide B. Thinning and growth. Journal of Forestry. 2001:20-25

[43] Giuggiola A, Ogée J, Rigling A, Gessler A, Bugmann H, Treydte K. Improvement of water and light availability after thinning at a xeric site: Which matters more? A dual isotope approach. New Phytologist. 2016;**210**(1):108-121

[44] Taeger S, Zang C, Liesebach M, Schneck V, Menzel A. Impact of climate and drought events on the growth of Scots pine (*Pinus sylvestris* L.) provenances. Forest Ecology and Management. 2013;**307**:30-42

[45] Dwyer JM, Fensham R, Buckley YM. Restoration thinning accelerates structural development and carbon sequestration in an endangered Australian ecosystem: Restoration thinning in natural regrowth. Journal of Applied Ecology. 2010;**47**(3):681-691

[46] Hoover C, Stout S. The carbon consequences of thinning techniques: Stand structure makes a difference. Journal of Forestry. 2007;**105**(5): 266-270

[47] Horner GJ, Baker PJ, Nally RM, Cunningham SC, Thomson JR, Hamilton F. Forest structure, habitat and carbon benefits from thinning floodplain forests: Managing early stand density makes a difference. Forest Ecology and Management. 2010;**259**(3):286-293

[48] Schaedel MS, Larson AJ, Affleck DLR, Belote RT, Goodburn JM, Page-Dumroese DS. Early forest thinning changes aboveground carbon distribution among pools, but not total amount. Forest Ecology and Management. 2017;**389**:187-198

[49] Lei X, Lu Y, Peng C, Zhang X, Chang J, Hong L. Growth and structure development of semi-natural larchspruce-fir (*Larix olgensis*–*Picea jezoensis*–*Abies nephrolepis*) forests in northeast China: 12-year results after thinning. Forest Ecology and Management. 2007;**240**(1-3):165-177

[50] Juodvalkis A, Kairiukstis L, Vasiliauskas R. Effects of thinning on growth of six tree species in north-temperate forests of Lithuania. European Journal of Forest Research. 2005;**124**(3):187-192

[51] Bradford JB, Palik BJ. A comparison of thinning methods in red pine: Consequences for stand-level growth and tree diameter. Canadian Journal of Forest Research. 2009;**39**(3):489-496

[52] Kuehne C, Weiskittel A, Pommerening A, Wagner RG. Evaluation of 10-year temporal and spatial variability in structure and growth across contrasting commercial thinning treatments in spruce-fir forests of northern Maine, USA. Annals of Forest Science. 2018;**75**(1):20

[53] Pretzsch H. Stand density and growth of Norway spruce (*Picea abies* (L.) Karst.) and European beech (*Fagus sylvatica* L.): Evidence from long-term experimental plots. European Journal of Forest Research. 2005;**124**(3):193-205

[54] Brooks JR, Mitchell AK. Interpreting tree responses to thinning and fertilization using tree-ring stable isotopes. New Phytologist. 2011;**190**(3):770-782

[55] Lagergren F, Lankreijer H, Kučera J, Cienciala E, Mölder M, Lindroth A. Thinning effects on pine-spruce forest transpiration in central Sweden. Forest Ecology and Management. 2008;**255**(7):2312-2323

[56] Gagné L, Sirois L, Lavoie L. Comparaison du volume et de la valeur des bois résineux issus d'éclaircies par le bas et par dégagement d'arbres-élites dans l'Est du Canada. Canadian Journal of Forest Research. 2016;**46**(11):1320-1329

[57] Schütz J-P, Ammann PL, Zingg A. Optimising the yield of Douglas-fir with an appropriate thinning regime. European Journal of Forest Research. 2015;**134**(3):469-480

[58] Curtis RO, Harrington CA, Brodie LC. Stand development 18 years after gap creation in a uniform Douglas-Fir plantation. In: Report No.: PNW-RP-610. USDA Forest Service; 2017. p. 38

[59] Davis LR, Puettmann KJ, Tucker GF. Overstory response to alternative thinning treatments in young Douglas-fir forests of Western Oregon. Northwest Science. 2007;**81**(1):1-14

[60] Willis JL, Roberts SD, Harrington CA. Variable density thinning promotes variable structural responses 14 years after treatment in the Pacific Northwest. Forest Ecology and Management. 2018;**410**:114-125

[61] Gardiner B, Blennow K, Carnus J-M, Fleischer P, Ingemarson F, Landmann G, et al. Destructive Storms in European Forests. Joensuu: European Forest Institute; 2010. p. 138

[62] Lindström A, Rune G. Root deformation in plantations of containergrown Scots pine trees: Effects on root growth, tree stability and stem straightness. In: Stokes A, editor. The Supporting Roots of Trees and Woody Plants: Form, Function and Physiology. Dordrecht: Springer Netherlands; 2000. pp. 31-39

[63] Schmidt M, Hanewinkel M, Kändler G, Kublin E, Kohnle U. An inventory-based approach for modeling single-tree storm damage— Experiences with the winter storm of 1999 in southwestern Germany. Canadian Journal of Forest Research. 2010;**40**(8):1636-1652

[64] Binkley D, Campoe OC, Gspaltl M, Forrester DI. Light absorption and use efficiency in forests: Why patterns differ for trees and stands. Forest Ecology and Management. 2013;**288**:5-13

[65] Lee MJ, García O. Plasticity and extrapolation in modeling mixedspecies stands. Forest Science. 2016;**62**(1):1-8

[66] Keskitalo E, Bergh J, Felton A, Björkman C, Berlin M, Axelsson P, et al. Adaptation to climate change in Swedish Forestry. Forests. 2016;**7**(2):28

[67] Mäkinen H, Isomäki A. Thinning intensity and long-term changes in increment and stem form of Norway spruce trees. Forest Ecology and Management. 2004;**201**(2-3):295-309

[68] Nilsson U, Agestam E, Ekö P-M, Elfving B, Fahlvik N, Johansson U, et al. Thinning of Scots pine and Norway spruce monocultures in Sweden effects of different thinning programmes on standlevel gross- and net stem volume

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[77] Aldea J, Bravo F, Bravo-Oviedo A, Ruiz-Peinado R, Rodríguez F, del Río M. Thinning enhances the species-specific radial increment response to drought in Mediterranean pine-oak stands. Agricultural and Forest Meteorology.

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[69] Sullivan TP, Sullivan DS.

[70] Varmola M, Salminen H, Timonen M. Thinning response and growth trends of seeded Scots pine stands at the arctic timberline. Silva

Fennica. 2004;**38**(1):71-83

2002;**36**(4):813-825

2001;**145**(1-2):137-149

2006;**63**(4):349-354

2015;**6**(12):2678-2702

[73] Peltola H. Swaying of trees in response to wind and thinning in a stand of Scots pine. Boundary Layer Meteorology. 1996;**77**(3-4):285-304

[74] Sharma M, Smith M, Burkhart HE, Amateis RL. Modeling the impact of thinning on height development of dominant and codominant loblolly pine trees. Annals of Forest Science.

[75] Mäkinen H, Isomäki A. Thinning intensity and growth of Scots pine stands in Finland. Forest Ecology and Management. 2004;**201**(2-3):311-325

[76] Moulinier J, Brais S, Harvey B, Koubaa A. Response of Boreal Jack Pine (*Pinus banksiana* Lamb.) stands to a gradient of commercial thinning intensities, with and without N fertilization. Forests.

[71] Peltola H, Miina J, Rouvinen I, Kellomäki S. Effect of early thinning on the diameter growth distribution along the stem of Scots pine. Silva Fennica.

[72] Bachofen H, Zingg A. Effectiveness of structure improvement thinning on stand structure in subalpine Norway spruce (*Picea abies* (L.) Karst.) stands. Forest Ecology and Management.

*Thinning: An Overview DOI: http://dx.doi.org/10.5772/intechopen.93436*

production. Studia Forestalia Suecica. 2010;**219**:1-46

*Silviculture*

[53] Pretzsch H. Stand density and growth of Norway spruce (*Picea abies* (L.) Karst.) and European beech (*Fagus sylvatica* L.): Evidence from long-term experimental plots. European Journal of Forest Research. 2005;**124**(3):193-205

[61] Gardiner B, Blennow K, Carnus J-M, Fleischer P, Ingemarson F,

Forest Institute; 2010. p. 138

pp. 31-39

[62] Lindström A, Rune G. Root

[63] Schmidt M, Hanewinkel M, Kändler G, Kublin E, Kohnle U. An inventory-based approach for modeling single-tree storm damage— Experiences with the winter storm of 1999 in southwestern Germany. Canadian Journal of Forest Research.

[64] Binkley D, Campoe OC, Gspaltl M, Forrester DI. Light absorption and use efficiency in forests: Why patterns differ for trees and stands. Forest Ecology and

2010;**40**(8):1636-1652

Management. 2013;**288**:5-13

2016;**62**(1):1-8

[65] Lee MJ, García O. Plasticity and extrapolation in modeling mixedspecies stands. Forest Science.

[66] Keskitalo E, Bergh J, Felton A, Björkman C, Berlin M, Axelsson P, et al. Adaptation to climate change in Swedish

[67] Mäkinen H, Isomäki A. Thinning intensity and long-term changes in increment and stem form of Norway spruce trees. Forest Ecology and Management. 2004;**201**(2-3):295-309

[68] Nilsson U, Agestam E, Ekö P-M, Elfving B, Fahlvik N, Johansson U, et al. Thinning of Scots pine and Norway spruce monocultures in Sweden effects of different thinning programmes on standlevel gross- and net stem volume

Forestry. Forests. 2016;**7**(2):28

Landmann G, et al. Destructive Storms in European Forests. Joensuu: European

deformation in plantations of containergrown Scots pine trees: Effects on root growth, tree stability and stem straightness. In: Stokes A, editor. The Supporting Roots of Trees and Woody Plants: Form, Function and Physiology. Dordrecht: Springer Netherlands; 2000.

[54] Brooks JR, Mitchell AK.

2011;**190**(3):770-782

2008;**255**(7):2312-2323

2016;**46**(11):1320-1329

2015;**134**(3):469-480

2017. p. 38

[58] Curtis RO, Harrington CA, Brodie LC. Stand development 18 years after gap creation in a uniform Douglas-Fir plantation. In: Report No.: PNW-RP-610. USDA Forest Service;

[56] Gagné L, Sirois L, Lavoie L. Comparaison du volume et de la valeur des bois résineux issus

d'éclaircies par le bas et par dégagement d'arbres-élites dans l'Est du Canada. Canadian Journal of Forest Research.

[57] Schütz J-P, Ammann PL, Zingg A. Optimising the yield of Douglas-fir with an appropriate thinning regime. European Journal of Forest Research.

[59] Davis LR, Puettmann KJ, Tucker GF. Overstory response to alternative thinning treatments in young

Douglas-fir forests of Western Oregon. Northwest Science. 2007;**81**(1):1-14

[60] Willis JL, Roberts SD, Harrington CA. Variable density thinning promotes variable structural responses 14 years after treatment in the Pacific Northwest. Forest Ecology and Management. 2018;**410**:114-125

Interpreting tree responses to thinning and fertilization using tree-ring stable isotopes. New Phytologist.

[55] Lagergren F, Lankreijer H, Kučera J, Cienciala E, Mölder M, Lindroth A. Thinning effects on pine-spruce forest transpiration in central Sweden. Forest Ecology and Management.

**54**

[69] Sullivan TP, Sullivan DS. Acceleration of old-growth structural attributes in lodgepole pine forest: Tree growth and stand structure 25 years after thinning. Forest Ecology and Management. 2016;**365**:96-106

[70] Varmola M, Salminen H, Timonen M. Thinning response and growth trends of seeded Scots pine stands at the arctic timberline. Silva Fennica. 2004;**38**(1):71-83

[71] Peltola H, Miina J, Rouvinen I, Kellomäki S. Effect of early thinning on the diameter growth distribution along the stem of Scots pine. Silva Fennica. 2002;**36**(4):813-825

[72] Bachofen H, Zingg A. Effectiveness of structure improvement thinning on stand structure in subalpine Norway spruce (*Picea abies* (L.) Karst.) stands. Forest Ecology and Management. 2001;**145**(1-2):137-149

[73] Peltola H. Swaying of trees in response to wind and thinning in a stand of Scots pine. Boundary Layer Meteorology. 1996;**77**(3-4):285-304

[74] Sharma M, Smith M, Burkhart HE, Amateis RL. Modeling the impact of thinning on height development of dominant and codominant loblolly pine trees. Annals of Forest Science. 2006;**63**(4):349-354

[75] Mäkinen H, Isomäki A. Thinning intensity and growth of Scots pine stands in Finland. Forest Ecology and Management. 2004;**201**(2-3):311-325

[76] Moulinier J, Brais S, Harvey B, Koubaa A. Response of Boreal Jack Pine (*Pinus banksiana* Lamb.) stands to a gradient of commercial thinning intensities, with and without N fertilization. Forests. 2015;**6**(12):2678-2702

[77] Aldea J, Bravo F, Bravo-Oviedo A, Ruiz-Peinado R, Rodríguez F, del Río M. Thinning enhances the species-specific radial increment response to drought in Mediterranean pine-oak stands. Agricultural and Forest Meteorology. 2017;**237-238**:371-383

[78] Fernández-de-Uña L, Cañellas I, Gea-Izquierdo G. Stand competition determines how different tree species will cope with a warming climate. Liang E, editor. PLoS One. 2015;10(3):e0122255.

[79] Martín-Benito D, Del Río M, Heinrich I, Helle G, Cañellas I. Response of climate-growth relationships and water use efficiency to thinning in a *Pinus nigra* afforestation. Forest Ecology and Management. 2010;**259**(5):967-975

[80] Schwinning S, Weiner J. Mechanisms determining the degree of size asymmetry in competition among plants. Oecologia. 1998;**113**(4):447-455

[81] Thomas AD, Walsh RPD, Shakesby RA. Nutrient losses in eroded sediment after fire in eucalyptus and pine forests in the wet Mediterranean environment of northern Portugal. CATENA. 1999;**36**(4):283-302

[82] Dobner M, Nicoletti MF, Arce JE. Influence of crown thinning on radial growth pattern of *Pinus taeda* in southern Brazil. New Forests. 2019;**50**(3):437-454

[83] Liziniewicz M, Ekö PM, Klang F. Effects of five tree-selection strategies when thinning spruce (*Picea abies*) stands: A case study in a field trail in southern Sweden. Scandinavian Journal of Forest Research. 2016;**31**(5):495-506

[84] Trouvé R, Bontemps J-D, Seynave I, Collet C, Lebourgeois F. Stand density, tree social status and water stress influence allocation in height and diameter growth of *Quercus petraea* (Liebl.), Mäkelä A, editor. Tree Physiology. 2015;35(10):1035-1046.

[85] Weiskittel A, Kenefic L, Seymour R, Phillips L. Long-term effects of precommercial thinning on the stem dimensions, form and branch characteristics of red spruce and balsam fir crop trees in Maine, USA. Silva Fennica. 2009;**43**(3):397-409

[86] Anton-Fernandez C, Burkhart HE, Strub M, Amateis RL. Effects of initial spacing on height development of Loblolly Pine. Forest Science. 2011;**57**(3):201-211

[87] Zhao D, Kane M, Borders BE. Growth responses to planting density and management intensity in loblolly pine plantations in the southeastern USA Lower Coastal Plain. Annals of Forest Science. 2011;**68**(3):625-635

[88] Schaedel MS, Larson AJ, Affleck DLR, Belote RT, Goodburn JM, Wright DK, et al. Long-term precommercial thinning effects on *Larix occidentalis* (western larch) tree and stand characteristics. Canadian Journal of Forest Research. 2017;**47**(7):861-874

[89] Valinger E, Sjögren H, Nord G, Cedergren J. Effects on stem growth of Scots pine 33 years after thinning and/ or fertilization in northern Sweden. Scandinavian Journal of Forest Research. 2019;**34**(1):33-38

[90] Martínez Pastur G, Soler R, Lencinas MV, Cellini JM, Peri PL. Long-term monitoring of thinning for silvopastoral purposes in *Nothofagus antarctica* forests of Tierra del Fuego, Argentina. Forest Systems. 2018;**27**(1):e01S

[91] Mehtätalo L, Peltola H, Kilpeläinen A, Ikonen V-P. The response of basal area growth of Scots pine to thinning: A longitudinal analysis of tree-specific series using a nonlinear mixed-effects model. Forest Science. 2014;**60**(4):636-644

[92] Sillett SC, Van Pelt R, Kramer RD, Carroll AL, Koch GW. Biomass and growth potential of *Eucalyptus regnans* up to 100 m tall. Forest Ecology and Management. 2015;**348**:78-91

[93] Sillett SC, Van Pelt R, Koch GW, Ambrose AR, Carroll AL, Antoine ME, et al. Increasing wood production through old age in tall trees. Forest Ecology and Management. 2010;**259**(5):976-994

[94] Stephenson NL, Das AJ, Condit R, Russo SE, Baker PJ, Beckman NG, et al. Rate of tree carbon accumulation increases continuously with tree size. Nature. 2014;**507**(7490):90-93

[95] Sohn JA, Saha S, Bauhus J. Potential of forest thinning to mitigate drought stress: A meta-analysis. Forest Ecology and Management. 2016;**380**:261-273

[96] Guiterman CH, Seymour RS, Weiskittel AR. Long-term thinning effects on the leaf area of *Pinus strobus* L. as estimated from Litterfall and individual-tree allometric models. Forest Science. 2012;**58**(1):85-93

[97] Peri PL, Martínez Pastur G, Monelos L. Natural dynamics and thinning response of young lenga (*Nothofagus pumilio*) trees in secondary forests of Southern Patagonia. Bosque Valdivia. 2013;**34**(3):5-6

[98] Aussenac G. Interactions between forest stands and microclimate: Ecophysiological aspects and consequences for silviculture. Annals of Forest Science. 2000;**57**(3):287-301

[99] Primicia I, Artázcoz R, Imbert J-B, Puertas F, Traver M-C, Castillo F-J. Influence of thinning intensity and canopy type on Scots pine stand and growth dynamics in a mixed managed forest. Forest Systems. 2016;**25**(2):e057

[100] Pretzsch H, Rais A. Wood quality in complex forests versus even-aged monocultures: Review and perspectives.

**57**

*Thinning: An Overview*

2016;**50**(4):845-880

2013;**23**(8):1735-1742

*DOI: http://dx.doi.org/10.5772/intechopen.93436*

[108] De las Heras J, Moya D, López-Serrano FR, Rubio E. Carbon

2013;**44**(3):457-470

2006;**237**(1-3):342-352

sequestration of naturally regenerated Aleppo pine stands in response to early thinning. New Forests.

[109] Blanco JA, Imbert JB, Castillo FJ. Influence of site characteristics and thinning intensity on litterfall production in two *Pinus sylvestris* L. forests in the western Pyrenees. Forest Ecology and Management.

[110] Finkral AJ, Evans AM. The effects of a thinning treatment on carbon stocks in a northern *Arizona ponderosa* pine forest. Forest Ecology and Management. 2008;**255**(7):2743-2750

[111] Jobbágy EG, Jackson RB. The distribution of soil nutrients with depth: Global patterns and the imprint of plants. Biogeochemistry. 2001;**53**:51-77

[112] Hoover CM, Heath LS. A commentary on 'Mineral soil carbon fluxes in forests and implications for carbon balance assessments': A deeper look at the data. GCB Bioenergy.

[113] Peri PL, Bahamonde HA, Lencinas MV, Gargaglione V, Soler R, Ormaechea S, et al. A review of silvopastoral systems in native forests of *Nothofagus antarctica* in southern Patagonia, Argentina. Agroforestry Systems. 2016;**90**(6):933-960

[114] Bréda N, Granier A, Aussenac G. Effects of thinning on soil and tree water relations, transpiration and growth in an oak forest (*Quercus* 

*petraea* (Matt.) Liebl.). Tree Physiology.

[115] Sohn JA, Hartig F, Kohler M, Huss J, Bauhus J. Heavy and frequent thinning promotes drought adaptation in *Pinus sylvestris* forests. Ecological Applications. 2016;**26**(7):2190-2205

2015;**7**(2):362-365

1995;**15**(5):295-306

[102] Fahlvik N, Ekö P-M, Pettersson N. Influence of precommercial thinning grade on branch diameter and crown ratio in *Pinus sylvestris* in southern Sweden. Scandinavian Journal of Forest

Research. 2005;**20**(3):243-251

[103] D'Amato AW, Bradford JB, Fraver S, Palik BJ. Forest management for mitigation and adaptation to climate

change: Insights from long-term

2011;**84**(2):149-157

[105] Skovsgaard JP, Stupak I,

Journal of Forest Research. 2006;**21**(6):470-488

2010;**40**(4):659-667

2009;**82**(1):87-104

[106] Keyser TL. Thinning and site quality influence aboveground tree carbon stocks in yellow-poplar forests of the southern Appalachians. Canadian Journal of Forest Research.

[107] Skovsgaard JP. Analysing effects of thinning on stand volume growth in relation to site conditions: A case study for even-aged Sitka spruce (*Picea sitchensis* (Bong.) Carr.). Forestry.

silviculture experiments. Forest Ecology and Management. 2011;**262**(5):803-816

[104] Jimenez E, Vega JA, Fernandez C, Fonturbel T. Is pre-commercial thinning compatible with carbon sequestration? A case study in a maritime pine stand in northwestern Spain. Forestry.

Vesterdal L. Distribution of biomass and carbon in even-aged stands of Norway spruce (*Picea abies* (L.) Karst.): A case study on spacing and thinning effects in northern Denmark. Scandinavian

Wood Science and Technology.

[101] D'Amato AW, Bradford JB, Fraver S, Palik BJ. Effects of thinning on drought vulnerability and climate response in north temperate forest ecosystems. Ecological Applications.

*Thinning: An Overview DOI: http://dx.doi.org/10.5772/intechopen.93436*

Wood Science and Technology. 2016;**50**(4):845-880

*Silviculture*

[85] Weiskittel A, Kenefic L, Seymour R,

[92] Sillett SC, Van Pelt R, Kramer RD, Carroll AL, Koch GW. Biomass and growth potential of *Eucalyptus regnans* up to 100 m tall. Forest Ecology and Management. 2015;**348**:78-91

[93] Sillett SC, Van Pelt R, Koch GW, Ambrose AR, Carroll AL, Antoine ME, et al. Increasing wood production through old age in tall trees. Forest Ecology and Management. 2010;**259**(5):976-994

[94] Stephenson NL, Das AJ, Condit R, Russo SE, Baker PJ, Beckman NG, et al. Rate of tree carbon accumulation increases continuously with tree size. Nature. 2014;**507**(7490):90-93

[95] Sohn JA, Saha S, Bauhus J. Potential of forest thinning to mitigate drought stress: A meta-analysis. Forest Ecology and Management. 2016;**380**:261-273

[96] Guiterman CH, Seymour RS, Weiskittel AR. Long-term thinning effects on the leaf area of *Pinus strobus* L. as estimated from Litterfall and individual-tree allometric models. Forest Science. 2012;**58**(1):85-93

[97] Peri PL, Martínez Pastur G, Monelos L. Natural dynamics and thinning response of young lenga (*Nothofagus pumilio*) trees in secondary forests of Southern Patagonia. Bosque

[98] Aussenac G. Interactions between forest stands and microclimate: Ecophysiological aspects and

consequences for silviculture. Annals of Forest Science. 2000;**57**(3):287-301

[99] Primicia I, Artázcoz R, Imbert J-B, Puertas F, Traver M-C, Castillo F-J. Influence of thinning intensity and canopy type on Scots pine stand and growth dynamics in a mixed managed forest. Forest Systems. 2016;**25**(2):e057

[100] Pretzsch H, Rais A. Wood quality in complex forests versus even-aged monocultures: Review and perspectives.

Valdivia. 2013;**34**(3):5-6

[86] Anton-Fernandez C, Burkhart HE, Strub M, Amateis RL. Effects of initial spacing on height development of Loblolly Pine. Forest Science.

[87] Zhao D, Kane M, Borders BE. Growth responses to planting density and management intensity in loblolly pine plantations in the southeastern USA Lower Coastal Plain. Annals of Forest Science. 2011;**68**(3):625-635

[88] Schaedel MS, Larson AJ,

Wright DK, et al. Long-term precommercial thinning effects on *Larix occidentalis* (western larch) tree and stand characteristics. Canadian Journal of Forest Research.

2017;**47**(7):861-874

2018;**27**(1):e01S

2014;**60**(4):636-644

Affleck DLR, Belote RT, Goodburn JM,

[89] Valinger E, Sjögren H, Nord G, Cedergren J. Effects on stem growth of Scots pine 33 years after thinning and/ or fertilization in northern Sweden. Scandinavian Journal of Forest Research. 2019;**34**(1):33-38

[90] Martínez Pastur G, Soler R, Lencinas MV, Cellini JM, Peri PL. Long-term monitoring of thinning for silvopastoral purposes in *Nothofagus antarctica* forests of Tierra del Fuego, Argentina. Forest Systems.

[91] Mehtätalo L, Peltola H,

Kilpeläinen A, Ikonen V-P. The response of basal area growth of Scots pine to thinning: A longitudinal analysis of tree-specific series using a nonlinear mixed-effects model. Forest Science.

2011;**57**(3):201-211

Phillips L. Long-term effects of precommercial thinning on the stem dimensions, form and branch characteristics of red spruce and balsam fir crop trees in Maine, USA. Silva Fennica. 2009;**43**(3):397-409

**56**

[101] D'Amato AW, Bradford JB, Fraver S, Palik BJ. Effects of thinning on drought vulnerability and climate response in north temperate forest ecosystems. Ecological Applications. 2013;**23**(8):1735-1742

[102] Fahlvik N, Ekö P-M, Pettersson N. Influence of precommercial thinning grade on branch diameter and crown ratio in *Pinus sylvestris* in southern Sweden. Scandinavian Journal of Forest Research. 2005;**20**(3):243-251

[103] D'Amato AW, Bradford JB, Fraver S, Palik BJ. Forest management for mitigation and adaptation to climate change: Insights from long-term silviculture experiments. Forest Ecology and Management. 2011;**262**(5):803-816

[104] Jimenez E, Vega JA, Fernandez C, Fonturbel T. Is pre-commercial thinning compatible with carbon sequestration? A case study in a maritime pine stand in northwestern Spain. Forestry. 2011;**84**(2):149-157

[105] Skovsgaard JP, Stupak I, Vesterdal L. Distribution of biomass and carbon in even-aged stands of Norway spruce (*Picea abies* (L.) Karst.): A case study on spacing and thinning effects in northern Denmark. Scandinavian Journal of Forest Research. 2006;**21**(6):470-488

[106] Keyser TL. Thinning and site quality influence aboveground tree carbon stocks in yellow-poplar forests of the southern Appalachians. Canadian Journal of Forest Research. 2010;**40**(4):659-667

[107] Skovsgaard JP. Analysing effects of thinning on stand volume growth in relation to site conditions: A case study for even-aged Sitka spruce (*Picea sitchensis* (Bong.) Carr.). Forestry. 2009;**82**(1):87-104

[108] De las Heras J, Moya D, López-Serrano FR, Rubio E. Carbon sequestration of naturally regenerated Aleppo pine stands in response to early thinning. New Forests. 2013;**44**(3):457-470

[109] Blanco JA, Imbert JB, Castillo FJ. Influence of site characteristics and thinning intensity on litterfall production in two *Pinus sylvestris* L. forests in the western Pyrenees. Forest Ecology and Management. 2006;**237**(1-3):342-352

[110] Finkral AJ, Evans AM. The effects of a thinning treatment on carbon stocks in a northern *Arizona ponderosa* pine forest. Forest Ecology and Management. 2008;**255**(7):2743-2750

[111] Jobbágy EG, Jackson RB. The distribution of soil nutrients with depth: Global patterns and the imprint of plants. Biogeochemistry. 2001;**53**:51-77

[112] Hoover CM, Heath LS. A commentary on 'Mineral soil carbon fluxes in forests and implications for carbon balance assessments': A deeper look at the data. GCB Bioenergy. 2015;**7**(2):362-365

[113] Peri PL, Bahamonde HA, Lencinas MV, Gargaglione V, Soler R, Ormaechea S, et al. A review of silvopastoral systems in native forests of *Nothofagus antarctica* in southern Patagonia, Argentina. Agroforestry Systems. 2016;**90**(6):933-960

[114] Bréda N, Granier A, Aussenac G. Effects of thinning on soil and tree water relations, transpiration and growth in an oak forest (*Quercus petraea* (Matt.) Liebl.). Tree Physiology. 1995;**15**(5):295-306

[115] Sohn JA, Hartig F, Kohler M, Huss J, Bauhus J. Heavy and frequent thinning promotes drought adaptation in *Pinus sylvestris* forests. Ecological Applications. 2016;**26**(7):2190-2205

[116] Fulé PZ, Waltz AEM, Covington WW, Heinlein TA. Measuring forest restoration effectiveness in reducing hazardous fuels. Journal of Forestry-Washington. 2001;**99**(11):24-29

[117] Fernandes PM, Vega JA, Jiménez E, Rigolot E. Fire resistance of European pines. Forest Ecology and Management. 2008;**256**(3):246-255

[118] Verkaik I, Espelta JM. Post-fire regeneration thinning, cone production, serotiny and regeneration age in *Pinus halepensis*. Forest Ecology and Management. 2006;**231**(1-3):155-163

[119] Bren L, Lane P, Hepworth G. Longer-term water use of native eucalyptus forest after logging and regeneration: The Coranderrk experiment. Journal of Hydrology. 2010;**384**(1-2):52-64

[120] Bréda N, Huc R, Granier A, Dreyer E. Temperate forest trees and stands under severe drought: A review of ecophysiological responses, adaptation processes and long-term consequences. Annals of Forest Science. 2006;**63**(6):625-644

[121] Sohn JA, Gebhardt T, Ammer C, Bauhus J, Häberle K-H, Matyssek R, et al. Mitigation of drought by thinning: Shortterm and long-term effects on growth and physiological performance of Norway spruce (*Picea abies*). Forest Ecology and Management. 2013;**308**:188-197

[122] Christina M, Laclau J-P, Gonçalves JLM, Jourdan C, Nouvellon Y, Bouillet J-P. Almost symmetrical vertical growth rates above and below ground in one of the world's most productive forests. Ecosphere. 2011;**2**(3):art27

[123] Foster TE, Schmalzer PA, Fox GA. Seasonal climate and its differential impact on growth of co-occurring species. European Journal of Forest Research. 2015;**134**(3):497-510

[124] Mainiero R, Kazda M. Depthrelated fine root dynamics of *Fagus sylvatica* during exceptional drought. Forest Ecology and Management. 2006;**237**(1-3):135-142

[125] Dieler J, Pretzsch H. Morphological plasticity of European beech (*Fagus sylvatica* L.) in pure and mixedspecies stands. Forest Ecology and Management. 2013;**295**:97-108

[126] Crecente-Campo F, Pommerening A, Rodríguez-Soalleiro R. Impacts of thinning on structure, growth and risk of crown fire in a *Pinus sylvestris* L. plantation in northern Spain. Forest Ecology and Management. 2009;**257**(9):1945-1954

[127] Peri PL, Dube F, Varella A. Silvopastoral Systems in Southern South America. Heidelberg, New York: Springer; 2016. pp. 270

[128] Martínez Pastur G, Peri PL, Huertas Herrera A, Schindler S, Díaz-Delgado R, Lencinas MV, et al. Linking potential biodiversity and three ecosystem services in silvopastoral managed forest landscapes of Tierra del Fuego, Argentina. International Journal of Biodiversity Science, Ecosystem Services & Management. 2017;**13**(2):1-11

[129] Peri PL, López DR, Rusch V, Rusch G, Rosas YM, Martínez Pastur G. State and transition model approach in native forests of Southern Patagonia (Argentina): Linking ecosystem services, thresholds and resilience. International Journal of Biodiversity Science, Ecosystem Services & Management. 2017;**13**(2):105-118

**59**

forestry [1–3].

**Chapter 4**

Change

*Janusz Szmyt*

**Abstract**

Differentiation of the Forest

of Adverse Effects of Climate

Structure as the Mitigation Action

For several decades, the attention of societies has been focused on potential environmental changes due to climate change. Although climate change is not a new phenomenon, in the recent two decades, there has been a growing interest of scientists trying to determine scenarios of trends and their potential impact on forest ecosystems and forestry. Despite the uncertainties of climate change and the response of forest ecosystem to change, the forest management must deal with these uncertainties. There is no single prescription on how to manage forest resources under climate change in order to fulfill all demands from society. Various strategies in forest management are developed to counteract the adverse effects of climate change on forests and forestry. The future forest management should implement the following three main strategies: create forests which are resistant to change, promote their greater resilience to change, and enable forests to respond to change. It is expected that the more the structured forest, the higher the adaptive capacity is expected. Experiment focused on the influence of different silvicultural procedures on the structure of Scots pine in Poland is presented. Achieved results indicated that the process of stand structure conversion is a long-term process and different

structural elements can be modified to different extents.

**1. Forests and forestry under climate change**

silviculture, *Pinus sylvestris*

**Keywords:** stand structure, adaptive management, stand diversity, adaptive

For several decades, the attention of societies has been focused on the information about potential changes in our environment due to the changing climate system. Although the climate change is not a new phenomenon, in the recent two decades, there has been a growing interest of scientists trying to determine trends in climate change and their potential impact on a number of areas of human life. The impact of these changes is also studied in the context of forest ecosystems and

As the Intergovernmental Panel on Climate Change (IPCC) reports indicate, one of the significant reasons for the observed climate change is the increasing content of greenhouse gases in the atmosphere and the human activity attributed

#### **Chapter 4**

*Silviculture*

[116] Fulé PZ, Waltz AEM, Covington WW, Heinlein TA. Measuring forest restoration effectiveness in reducing hazardous fuels. Journal of Forestry-Washington.

[117] Fernandes PM, Vega JA, Jiménez E, Rigolot E. Fire resistance of European pines. Forest Ecology and Management.

[124] Mainiero R, Kazda M. Depthrelated fine root dynamics of *Fagus sylvatica* during exceptional drought. Forest Ecology and Management.

[125] Dieler J, Pretzsch H. Morphological plasticity of European beech (*Fagus sylvatica* L.) in pure and mixedspecies stands. Forest Ecology and Management. 2013;**295**:97-108

Pommerening A, Rodríguez-Soalleiro R. Impacts of thinning on structure, growth and risk of crown fire in a *Pinus sylvestris* L. plantation in northern Spain. Forest Ecology and Management.

2006;**237**(1-3):135-142

[126] Crecente-Campo F,

2009;**257**(9):1945-1954

Springer; 2016. pp. 270

2017;**13**(2):1-11

[127] Peri PL, Dube F, Varella A. Silvopastoral Systems in Southern South America. Heidelberg, New York:

[128] Martínez Pastur G, Peri PL, Huertas Herrera A, Schindler S, Díaz-Delgado R, Lencinas MV, et al. Linking potential biodiversity and three ecosystem services in silvopastoral managed forest landscapes of Tierra del Fuego, Argentina. International Journal of Biodiversity Science, Ecosystem Services & Management.

[129] Peri PL, López DR, Rusch V, Rusch G, Rosas YM, Martínez Pastur G. State and transition model approach in native forests of Southern Patagonia (Argentina): Linking ecosystem services, thresholds and resilience. International Journal of Biodiversity Science, Ecosystem Services & Management. 2017;**13**(2):105-118

[118] Verkaik I, Espelta JM. Post-fire regeneration thinning, cone production,

serotiny and regeneration age in *Pinus halepensis*. Forest Ecology and Management. 2006;**231**(1-3):155-163

[119] Bren L, Lane P, Hepworth G. Longer-term water use of native eucalyptus forest after logging and regeneration: The Coranderrk experiment. Journal of Hydrology.

[120] Bréda N, Huc R, Granier A, Dreyer E. Temperate forest trees and stands under severe drought: A review of ecophysiological responses, adaptation processes and long-term consequences. Annals of Forest Science.

[121] Sohn JA, Gebhardt T, Ammer C, Bauhus J, Häberle K-H, Matyssek R, et al. Mitigation of drought by thinning: Shortterm and long-term effects on growth and physiological performance of Norway spruce (*Picea abies*). Forest Ecology and

Management. 2013;**308**:188-197

[122] Christina M, Laclau J-P,

Gonçalves JLM, Jourdan C, Nouvellon Y, Bouillet J-P. Almost symmetrical vertical growth rates above and below ground in one of the world's most productive forests. Ecosphere. 2011;**2**(3):art27

[123] Foster TE, Schmalzer PA, Fox GA. Seasonal climate and its differential impact on growth of co-occurring species. European Journal of Forest Research. 2015;**134**(3):497-510

2001;**99**(11):24-29

2008;**256**(3):246-255

2010;**384**(1-2):52-64

2006;**63**(6):625-644

**58**
