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The study of the distribution and abundance of elements within landscapes, the origins of these elements, and their impacts on organisms and processes. A landscape may be thought of as a heterogeneous assemblage or mosaic of internally uniform elements or patches, such as blocks of forest, agricultural fields, and housing subdivisions. Biogeographers, land-use planners, hydrologists, and ecosystem ecologists are concerned with patterns and processes at large scale. Landscape ecologists bridge these disciplines in order to understand the interplay between the natural and human factors that influence the development of landscapes, and the impacts of landscape patterns on humans, other organisms, and the flows of materials and energy among patches. Much of landscape ecology is founded on the notion that many observations, such as the persistence of a small mammal population within a forest patch, may be fully understood only by accounting for regional as well as local factors.
Factors that lead to the development of a landscape pattern include a combination of human and nonhuman agents. The geology of a region, including the topography and soils along with the regional climate, is strongly linked to the distribution of surface water and the types of vegetation that can exist on a site. These factors influence the pattern of human settlement and the array of past and present uses of land and water. One prevalent effect of humans is habitat fragmentation, which arises because humans tend to reduce the size and increase the isolation among patches of native habitat.
The pattern of patches on a landscape can in turn can have direct effects on many different processes. The structure and arrangement of patches can affect the physical movement of materials such as nutrients or pollutants and the fate of populations of plants and animals. Many of these impacts can be traced to two factors, the role of patch edges and the connectedness among patches.
The boundary between two patches often act as filters or barriers to the transport of biological and physical elements. As an example, leaving buffer strips of native vegetation along stream courses during logging activities can greatly reduce the amount of sediment and nutrients that reach the stream from the logged area. Edge effects can result when forests are logged and there is a flux of light and wind into areas formerly located in the interior of a forest. In this example, edges can be a less suitable habitat for plants and animals not able to cope with drier, high-light conditions. When habitats are fragmented, patches eventually can become so small that they are all edge. When this happens, forest interior dwellers may become extinct. When patch boundaries act as barriers to movement, they can have pronounced effects on the dynamics of populations within and among patches. In the extreme, low connectivity can result in regional extinction even when a suitable habitat remains. This can occur if populations depend on dispersal from neighboring populations. When a population becomes extinct within a patch, there is no way for a colonist to reach the vacant habitat and reestablish the population. This process is repeated until all of the populations within a region disappear. Landscape ecologists have promoted the use of corridors of native habitat between patches to preserve connectivity despite the fragmentation of a landscape.