*Forest Degradation under Global Change*

can all contribute to deforestation and forest degradation [4]. Specifically on forest degradation due to stem removals, eleven drivers were identified, namely, forest fires, firewood collection, grazing by wildlife, domesticated animals, carving, poles, shifting cultivation, timber, and mining activities [15]. A higher number of stems/ha/year were removed by shifting cultivation, followed by charcoal, natural death, firewood collection, and poles. In terms of carbon, however, higher above-ground carbon removals were caused by timber followed by fire, shifting cultivation, charcoal, and natural death.

When agriculture leads to the permanent conversion of forest into agricultural land use that is deforestation. However, when there is shifting cultivation within a landscape that is defined primarily as a forest, that is, forest degradation. Forest degradation is also defined when there is agriculture under the forest canopy. This is practiced for some crops that are shade-tolerant or even shadedemanding, such as some types of spice crops. Agriculture is the primary cause of deforestation and forest degradation worldwide, accounting for over 80% of total deforestation in developing nations [2]. Agricultural expansion in form of shifting cultivation and encroachment, which is characterized by a low level of technology and o low agricultural yield [16]. A variety of factors, including cultivation techniques, soil fertility, market potential, population expansion, and perhaps pertinent policies, will influence the length of the fallow and cultivation periods [17]. When the fallow period is shortened for shifting cultivation, carbon stocks are degraded. Agricultural expansion rather than intensification was due to inadequate farming technology, low productivity that resulted from it, and low returns on inputs [18].

Fuelwood and charcoal production are major contributors to forest degradation in Tanzania. This is owing to the fact that the primary source of energy is in the majority of Tanzanian households. Wood biomass is collected for use as fuel or charcoal for both home and commercial purposes. The extraction of adequate fuelwood stocks to damage the forest is a significant aspect. Bailis et al. [19] created a geographical supply and demand technique to quantify greenhouse gas emissions associated with wood harvesting for fuel consumption. Woodfuel Integrated Supply/Demand Overview Mapping (WISDOM). Their findings revealed that the distance to the road had a substantial impact on the occurrence of stumps cut for charcoal. According to field observations and interviews, the geology of the area (slope, soil, presence of stones, and availability of drinking water) and preferred species are important variables in determining the location of charcoal production.

Selective timber harvesting can degrade forest carbon stocks, especially in humid tropical forests [7]. Biomass is lost during harvesting operations due to a number of factors, including wood tree felling and damage to trees surrounding the felled trees. There is both illegal and legitimate timber harvesting. Biomass loss has the potential to deplete humid tropical forest carbon stocks [17].

The influence of fire on forests is multifaceted; fires might be ground fires that burn smaller trees and understory or major stand-replacing fires. Fires reduce the rate of forest regrowth and succession from grassland to forest, resulting in continuous grassland and bushland [17].

When grazing animals are allowed on forest land, they both browse and trample young and regenerating trees, killing or damaging them. This causes forest degradation because young seedlings do not survive, and tree girdling causes the eventual death of larger trees (**Table 4**).


#### **Table 4.**

*Main regions for forest degradation in Tanzania.*

#### **3.5 Methods of monitoring and assessment of forest degradation**

The effects of forest degradation are expected to vary depending on location, forest type, and degree of degradation, making it challenging to detect with medium resolution remote sensing, such as Landsat. There are two types of accounting: land-based and activity-based. Activity-based accounting analyzes emissions independently for each activity and evaluates numerous human activities that cause forest degradation. Regardless of the activities that occur, land-based accounting determines the change in carbon stocks in a specific area of land [17].

Estimates of subsistence wood extraction may be obtained using indirect remote sensing methods. Biomass sampling yields zero-inflated continuous data that challenges conventional statistical approaches. To predict biomass loss as a function of distance to the nearest settlement, Dons et al. [21] employed Tweedie Compound Poisson distributions from the exponential dispersion family in conjunction with GLM. Estimating removals is commonly done by measuring the diameter at breast height (D). The calculated D is then used to calculate biomass and volume using allometric formulae used SD to generate equations for calculating volume, aboveground biomass, and belowground biomass in Tanzanian miombo woods. They analyzed land use and cover maps over a 15-year period by dividing the estimated individual tree volume by the estimated age of the stump.

Distance to populations, urban centers, and roadways are examples of proxy variables that can be used to measure forest degradation [13]. Spatial models that imply a relationship between forest degradation and distance from populated areas, highways, and the forest boundary can be a valuable tool for determining the degree of forest deterioration. In this case, spatial models that imply a relationship between forest degradation and distance from populated areas, highways, and the forest boundary can be a useful tool for estimating the degree of forest deterioration [13]. Focusing on remotely sensed deforestation might miss significant declines in forest quality. Ahrends et al. [8] recommend the use of fast field assessments in conjunction with remote sensing to provide early warning and to allow for prompt and adequately focused conservation and policy responses.

#### **3.6 Institutions involved in efforts to control forest degradation**

To properly manage forest resources, it is not sufficient to comprehend different tree species, their regeneration strategies and extraction techniques and rates, for

#### *Forest Degradation in Tanzania: A Systematic Literature Review DOI: http://dx.doi.org/10.5772/intechopen.107157*

instance. Institutions must be involved in determining who has access to environmental resources, how much can be extracted, when, and how. Tanzania has made major advancements in the management of its forest resources since the early 1990s. Community-based forest management (CBFM) and joint forest management have been implemented as part of the phases (JFM). The two strategies are collectively known as participatory forest management (PFM) [22].

Community-based forest management (CBFM) in Tanzania has contributed to improving forest conditions and in some cases improving livelihoods. PFM has been demonstrated to reinforce forest bureaucrats' and other specialists' dominance at the expense of local autonomy and decision-making, which was both a normative objective in and of itself and a major premise underlying its promises of enhancing local livelihoods and forest conservation [23]. Tanzania's Forest Act of 2002 transferred forest resource ownership and management responsibilities to local communities. The objectives of community-based forest management (CBFM) include enhancing rural livelihoods, protecting and regenerating forest resources, and fostering good governance. State-owned forests on the reserved property are managed jointly by community organizations that rely on the forests for their livelihood [23].

## **3.7 Spatial distribution of studies on forest degradation in Tanzania**

The most mentioned region was Dar es Salaam, while the list mentioned was Rukwa when the names of the regions were searched from the whole document (**Figure 4**). However, when the names of the regions were searched only from the titles of the documents, only Kigoma had two mentions. The other mentioned regions were only mentioned once, while the rest had no mention in the title. The spatial distribution of studies on forest degradation may be influenced by a number of factors pertaining to a region, including existing forests and their characteristics, drivers of forest degradation, and proximity and accessibility of the region for research.

#### **Figure 4.**

*The spatial distribution of studies on forest degradation in Tanzania is indicated by number of times a region is mentioned in the title or the number of documents mentioning the region.*

## **4. Conclusions and recommendations**

There were more studies more recently, especially increasing sharply after the year 2000, peaking in 2016 and 2017, and then declining. The increasing interest in forest degradation may be related to more recognition of forest degradation as an important aspect of forest management, especially in comparison to deforestation, which received and continues to receive more attention than forest degradation. The increase in the number of publications toward 2016 and the decline after 2017 may also be related to a big research program that funded many projects related to forest management in general and forest degradation in one way or another. Before and after this program the fewer number of publications may indicate the significance of a focused research program that enhances the number of country-specific projects that get funded. The most frequent keywords taken from titles and abstracts were Tanzania, trees, and REDD+. Forest transition model, drivers, and monitoring were among the least frequent keywords. Keyword clusters formed by VOSviewer appear to be based on numerical correlations without meaningful interpretation of research themes.

Most terms are mentioned less frequently in the document title than in the document as a whole. This indicates that more studies are general on forest degradation than specific on the research terms. This represents research gaps for the research topics represented by the research terms. Some terms are covered less than expected, given their significance in forest degradation. The number of studies one may find on a research topic may depend on the term used to search the studies. For example, agriculture returns more research documents than cultivation. In some cases, this is affected by small differences in the spelling out of the research term. The estimated annual volume removals exceed the estimated mean annual increment indicating forest management in Tanzania is not sustainable. Various studies have found a variety of causes of forest degradation, including deforestation and forest degradation, agricultural expansion, wood extraction and settlement area agriculture, fuel wood production, unsustainable timber extraction, and pasture expansion. The effects of forest degradation are expected to vary depending on location, forest type, and degree of degradation, making it challenging to detect with medium resolution remote sensing, such as Landsat. There are two types of accounting: land-based and activity-based. Activity-based accounting analyses emissions independently for each activity and evaluates numerous human activities that cause forest degradation. Regardless of the activities that occur, land-based accounting determines the change in carbon stocks in a specific area of land. Tanzania has made major advancements in the management of its forest resources since the early 1990s. Community-based forest management (CBFM) and joint forest management (JFM) have been implemented. The most mentioned region was Dar es Salaam, while the list mentioned was Rukwa when the names of the regions were searched from the whole document. However, when the names of the regions were searched only from the titles of the documents, only Kigoma had two mentions. The other mentioned regions were only mentioned once, while the rest had no mention in the title. It is expected that forest stakeholders will find the analysis presented in this study useful. Furthermore, the stakeholders will find interest in addressing temporal, spatial, and thematic research gaps highlighted by this chapter. Temporally, the declining number of publications reported needs to be addressed. Spatially, some administrative regions are underrepresented in the literature. Thematically, more specific research on topics related to forest degradation needs to be carried out.

*Forest Degradation in Tanzania: A Systematic Literature Review DOI: http://dx.doi.org/10.5772/intechopen.107157*
