Definition of the Edge Effect

The edge effect is the tendency, within a given ecotone, to exhibit signs of increase among the variety and density of plant and animal life. An ecotone is the area between two different environmental types; which may contain features of the environment on either side. Ecologists typically observe such a phenomenon at the edge or border between two distinctly different ecological zones. The edge effect can occur either naturally or be induced by artificial means.

Ecotones

• An ecotone is the area between two distinctly different ecological types. The ecotone adjoining these different zones will contain features of both and be a sort of blending between the two. Examples of ecotones could include the sparse grasslands between a desert and a fertile plain or the area of a mountainside that shifts from the forest below to the frozen rocky summits above. Mountain ranges are excellent examples of ecotones due to the numerous climate and ecological differences that exist from ground level to their peak. The area of transition between each layer of distinctly different ecology's on the mountain's face is an ecotone.

The Edge Effect

• The ecotone will contain examples of plant and animal life found in both ecological zones that it joins. However, the ecotone may include some species that exist only within the ecotone itself. Generally the density of a given species is greater in the "pure" environment. When the boundary between two ecological environments explodes with a high density of specimens from both adjoining areas, you have what ecologists refer to as the edge effect.

Naturally Occurring Edge Effect

• As plant and animal life from each environment converge at or cross the ecotone, they essentially transplant seeds or offspring into the border between their respective habitats. Often these seeds or offspring remain within the ecotone and a sharp increase in population density is observed. Life from both sides of the ecotone accumulate and remain, thus imprinting aspects of each onto the border between them.

Man-Made Edge Effect

• As a species, mankind has altered the environments they inhabit all across the globe. The destruction of a given global ecosystem for the development of housing communities or industrial facilities creates artificial ecotones. New borders are formed between man-made environments and naturally existing ones. As an animal's habitat is destroyed or encroached upon, that species must find new resources. This creates artificial ecotones between housing communities and woodland areas or on either side of a highway that now splits one ecological zone into two separate halves. In this latter example, the highway itself forms a sort of man-made ecotone.

Intentional Edge Effect

• There are times when humans create artificial ecotones intentionally. Examples of this are:
  --Alley cropping, when trees and agricultural crops are combined to produce hybrid plant life.
  --Chinampas, a system of parallel canals and banks that help establish irrigation systems to fertilize crops or increase the ability of fishermen to catch large amounts of fish by herding them into specially designed ponds
  --Municipal planning, when designing a town or settlement, project planners may intentionally alter certain aspects of the landscape to assist with drainage or create recreational areas such as urban/suburban gardens and parks
  Any of these would inevitably constitute a change in local environments and thus establish artificial ecotones.