What Is an Edge Habitat

Across the globe, human development has fragmented once-continuous landscapes and ecosystems into isolated patches of natural habitat. Roads, towns, fences, canals, reservoirs, and farms are all examples of human artifacts that alter the pattern of the landscape. At the edges of developed areas, where natural habitats meet encroaching human habitats, animals are forced to adapt quickly to their new circumstances--and a closer look at the fate of these so-called edge species can give us sobering insights into the quality of the wild lands that remain. The health of any natural ecosystem depends significantly on two factors: the overall size of the habitat, and what is happening along its edges. For example, when human development cuts into an old-growth forest, the newly exposed edges are subjected to a series of microclimatic changes, including increases in sunlight, temperature, relative humidity, and exposure to wind. Plantlife and Microclimate Create New Habitats Plants are the first living organisms to respond to these changes, usually with increased leaf-fall, elevated tree mortality, and an influx of secondary-successional species. In turn, the combined changes in plant life and microclimate create new habitats for animals. More-reclusive bird species move to the interior of the remaining woodland, while birds better adapted to edge environments develop strongholds on the periphery. Populations of larger mammals like deer or big cats, which require large areas of undisturbed forest to support their numbers, often decrease in size. If their established territories have been destroyed, these mammals must adjust their social structure to accommodate the closer quarters of the remaining forest. Fragmented Forests Resemble Islands Researchers have found that fragmented forests resemble nothing so much as islands. The human development that surrounds a forest island acts as a barrier to animal migration, dispersal, and interbreeding (its very difficult for any animals, even relatively smart ones, to cross a busy highway!) In these island-like communities, species diversity is governed largely by the size of the remaining intact forest. In a way, this is not all bad news; the imposition of artificial constraints can be a major driver of evolution and the flourishing of better-adapted species. The problem is that evolution is a long-term process, unfolding over thousands or millions of years, while a given animal population may disappear in as little as a decade (or even a single year or month) if its ecosystem has been wrecked beyond repair. The changes in animal distribution and population that result from fragmentation and the creation of edge habitats illustrate how dynamic a cut-off ecosystem can be. It would be ideal if—when the bulldozers have disappeared—the environmental damages subsided; unfortunately, this is rarely the case. The animals and wildlife left behind must begin a complex process of adaptation and a long search for a new natural balance. Edited on February 8, 2017, by Bob Strauss