Edge Effect Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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An edge effect refers to the effect of a prevailing boundary between contrasting spatial environments within an ecosystem or landscape. Landscapes are comprised of heterogeneous mosaics of habitat patches of varying size, shape and quality; these characteristics change over space and time. The edges or boundaries between habitat patches have implications for ecological processes between patches (e.g., animal movement) as well as within them (e.g., light penetration from patch edge to interior affecting within patch resource availability). The spatial configuration ofpatches–or landscape spatial pattern–includes the degree of fragmentation of or connectivity among habitat patches within the landscape, thereby influencing ecosystem and landscape–level processes such as seasonal animal migration, effective range and dispersal, as well as the ecological impacts of natural or anthropogenic disturbance.

Edge regions among contrasting environments within a landscape are often referred to as ecotones. An example of a commonly considered edge is that between a forest patch and an adjacent non-forest land cover, such as pasture. Such an edge would define a sharp ecotone, and the forest patch would be characterized by a gradient of environmental conditions from its edge to its interior, with varying degrees of available light, ambient air temperature, wind exposure and soil moisture conditions. Close to the forest/nonforest edge, penetration of light and wind into the forest patch creates microhabitats that favor particular light/gap-loving, opportunistic plantand animal species. Increased “understory” growth closer to forest edges because of an increase in the dominance of light-loving plants, combined with lower soil moisture conditions may increase the risk of forest fires at edge locations, further creating new edge areas.

Widespread fragmentation of eastern and Midwestern forests in the United States has increased the abundance of the pasture-loving, brown-headed cowbird, which increasingly parasitizes the nests of interior-dwelling forest birds, driving a widespread reduction in their populations. Predation on bay scallops by fish and invertebrate species is much greater in patchy seagrass areas than in large homogenous expanses of seagrass.

The ratio of forest patch edge to its interior area is one commonly used metric in the field of landscape ecology, and characterizes the degree of forest fragmentation and edge habitat in a landscape. While much of landscape ecological research has focused on the quantification of landscape pattern, including edge-interior ratios and fragmentation and connectivity indices, increasingly studies are examining the ways in which such patterns influence ecological processes, and edge effects comprise a significant area of focus. It is estimated that the forested area of the Amazon Basin that was subject to edge effects in 1988 by virtue of being located within 1 kilometer of a deforested site (341,000 square kilometers) exceeded the extent of actual deforestation (approximately 230,000 square kilometers). Several anthropogenic environmental changes, particularly changesin land use and cover, thus have both direct and indirect consequences for ecological systems.

Bibliography:

A. Irlandi, W.G. Ambrose, and B.A. Orando, “Landscape Ecology and the Marine Environment: How Spatial Configuration of Seagrass Habitat Influences Growth and Survival of the Bay Scallop,” Oikos (v.72, 1995);
E. Ricklefs and G.L.Miller, Ecology, 4th ed. (W.H. Freeman and Company, 2000);
L. Skole and C. Tucker, “Tropical Deforestation and Habitat Loss Fragmentation in the Amazon: Satellite Data From 1978-1988,” Science (v.260, 1993).