**1. Introduction: variability at different spatial and temporal scales**

A given forest ecosystem is part of a landscape ecology matrix that develops as a whole and in which several processes operate in variable spatial and temporal scales. Forest dynamics and spatial variability are closely linked, involving the effects of biologic processes and external factors, which occur at a wide range of spatial scales. In turn, spatial variation of environmental conditions creates variable abiotic templates where forest communities develop. In the forest ecosystem, many aspects change in time and space, whether as a result of its own process or influenced by disturbances. The ecosystem functioning, in its various expressions, emphasizes the internal dynamics of the system in a particular state [1–3].

At the landscape level, different characteristics are involved, such as the amount of *habitat,* patch size, the landscape mosaic and connectivity, which are under the scope of biological conservation, ecological restoration, forest management, landscape ecology and land management [4]. Different management levels may be more or less dependent or related. In turn, different spatial scales can also be considered (local, regional and national).

The spatial pattern of forest patches involves elements such as size, quantity, type, proportion, shape and connectivity [5]. The landscape pattern may affect the

A disturbance is any event that affects or disrupts a particular ecological process

or ecosystem development; modifies the population structure; and changes the availability of a particular resource or the physical environment [6, 10, 14, 15]. A disturbance may be essentially described according to its type, frequency, magnitude or severity, extent and return period. The relative importance of each distur-

The disturbance *type* is one of the most important characteristics of a disturbance regime. Disturbances may be biotic or abiotic, natural or anthropogenic, as well as endogenous or exogenous. Endogenous disorders are an integral part of the autogenic ecosystem development process. The potential to create endogenous disturbances varies with the species, the forest stand and development. The control and intervention on destabilizing forces are important for the development and stability, and the ability to minimize certain effects can be assessed, such as loss of

The *magnitude* may affect more or less the existing plant mass. Some disturbances may destroy all vegetation, while others may leave some trees or other vegetation, which will influence the recovery process, depending on the number of remaining trees, species and position in the canopy. Major exogenous disturbances (fire, storm and clearcutting) result in a reduction or elimination of primary production and have different consequences in terms of biomass and export nutrients. A major disturbance may have an appreciable effect on the subsequent development of the forest ecosystem. For example, a fire may destroy a large part or all of the biomass and suppress primary production. At the same time, nutrients removed by volatilization and leaching can increase soil erosion. A clearcutting also removes a significant amount of nutrients present in the exploited material. A storm with the loss of many trees affects also the primary production; however, the biomass may remain in the system. Soil erosion, which can occur as a result of intensive logging, soil tillage or fire, has a strong negative impact on the ecosystem. A clearcutting or fire leads to the destruction of important hydrological, nutritional and biological soil properties. A clearcutting, particularly on steep slopes and thin soils, may lead to

long-time changes on soil structure and the ecosystem biogeochemistry.

important characteristics that may affect the ecosystem response.

The disturbances *frequency* can be relatively variable and depend on the influence of various factors, both natural and anthropogenic. Typically, larger scale natural disturbances occur over longer periods of time. Disturbances may occur regularly or irregularly in time and space, which will be reflected in the stand characteristics and development. The *time* and *duration* of a disturbance are also

The disturbance *extent* influences on the composition and structure of the stand,

Other relevant elements to consider in stand development are related to the initial conditions after a disturbance, the residual material and stand structural characteristics. A disturbance can create gaps of different size and shape, which may affect stand characteristics and dynamics. A given disturbance may affect different tropic and biological levels. The ecological effects due to disturbances and vegetation development vary with species. The resilience and the community type that are established after a disturbance are highly dependent on the ecosystem characteristics, the site conditions and the species that survive after a disturbance. Plants have different anatomical and physiological characteristics, with different adaptation and regenera-

affecting the microclimatic conditions and colonization capacity from the surrounding areas. A disturbance may intervene at wide range of spatial scales (tree,

tion mechanisms, which allow them to face and survive certain disturbances. A group of trees that develops after a disturbance is designated in some literature as *cohort* [9, 16]. The age range of the cohort may vary according to the

bance varies according to their characteristics and the type of forest.

*Spatial and Temporal Variability Regarding Forest: From Tree to the Landscape*

*DOI: http://dx.doi.org/10.5772/intechopen.91701*

water and nutrients.

stand and landscape).

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#### **Figure 1.**

*Forest management considering different spatial scales: tree, forest stand and landscape. Fluxes and interconnections occur among these spatial scales.*

ecological processes and the disturbances regime [6]. The spatial heterogeneity in forested landscapes may derive from different causes, including changes in ecological conditions, biotic interactions, developmental stages, land uses and disturbances.

In this chapter, the forest is assessed considering the variability at different spatial scales: the landscape, the forest population and the tree (**Figure 1**). A forest, of different size, is viewed as a part of the landscape, which might be structured according to a physiographic or natural model. A forest stand is considered a management unit that can be differentiated with a certain number of site and vegetal characteristics.

The understanding of the forest ecosystem's functioning and dynamics has improved over the past decades [7–13]. A better knowledge of their dynamics is important to forestry, providing a better decision support of the most appropriate practices to achieve certain objectives.
