Landscape ecology is the study of the causes and ecological consequences of spatial pattern in landscapes. While there is no specific spatial extent that defines a landscape, most landscape ecologists are interested in large areas ranging from a few square kilometers to entire continents. Within landscapes it is usually possible to define a series of different ecosystem types occurring as patches within the greater landscape. For example, in an agricultural landscape the patches might be different fields, woodlots, hedgerows, buildings, and ponds. The goal of a landscape ecologist is to understand and describe landscape structure; how this structure influences the movement of organisms, material, or energy across the landscape; and how and why landscape structure changes over time.
A landscape's structure can be quantified by describing characteristics of patches, such as their number, size, shape, position, and composition. Landscape ecologists have defined measures to quantify each of these attributes. For example, a shape index has been defined as the ratio of the patch's perimeter to the perimeter of a circle the same area as the patch. A circular patch would have the value of 1, and as the patch became more convoluted in shape, its shape index would increase in value.
A landscape's structure has an important influence on various ecological processes occurring in the landscape. For example, consider two landscapes having equal areas of forest and agricultural land. In one landscape the forest is divided into many small patches, whereas in the other landscape the forested area occurs as one large patch. The more fragmented landscape will provide more habitat to those organisms that thrive at boundaries between two ecosystem types, whereas the less fragmented landscape will be better for those species that require larger areas of undisturbed forest. So, just knowing what percentage of the landscape is forest versus cropland is not sufficient to predict what species may occur; it is also important to know how the patches are distributed across the landscape.
Another example of how landscape structure can be important comes from studies of lakes within a forested landscape. The position of a lake within the landscape can be an important determinant of the lake's physical, chemical, and biological characteristics. Because water flows downhill, lakes that are lower in the landscape receive more water from streams and groundwater than lakes higher in the flow system, which receive most of their water from precipitation. Lakes higher in the landscape tend to be smaller, more dilute chemically, and have fewer species of fish than lakes lower in the landscape, even though all of the lakes in the landscape experience the same weather and are situated in the same geological substrate .
Landscape structure can change through natural geological or biological processes. Earthquakes, volcanoes, and landslides are examples of geological processes. The work of beavers building a dam to flood an area is an example of a biological activity that can change landscape structure. Human activity, such as the clearing of forest land for agriculture or the expansion of urban areas, has also caused significant changes in landscape structure. These changes in structure, whether caused by natural forces or by humans, can have significant impacts on the ecology of landscapes.
Although landscape ecology is a relatively new scientific discipline, since the 1980s landscape ecologists have begun to understand how to characterize landscape structure, how landscape structure influences ecological processes, and how landscape structure changes.
Timothy K. Kratz
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Turner, Monica Goigel. Landscape Ecology in Theory and Practice: Pattern and Process. New York: Springer, 2001.