An ecotone is a location where two distinct ecosystems meet and have some characteristics of both systems. In addition to containing some species from each ecosystem, ecotones may also contain species that are specific to the particular ecotone, or to ecotones in general, because they are able to exploit resources from both ecosystems.
The ability of ecotones to support a greater variety of species than the adjacent ecosystems is referred to as the edge effect, and it plays an important role in maintaining biodiversity.
Ecotones can be of various widths, ranging from just a few meters to hundreds of meters or even kilometers, depending on the types of ecosystems, environmental gradients, human activity and natural disturbances. Examples of narrow ecotones are the boundary between a forest and a field, between a forest and a desert, between a salt marsh or lake and dry land, and where an urban environment meets a wilderness area.
Another example would be the meeting of a cliff and the flat land above or below it. This is because cliffs provide various microhabitats that are different from flat land and which can host specialized species, such as plants that thrive in the different sunlight and moisture conditions on cliffs and birds that require the safe nesting conditions that cliffs can provide.
The lengths of ecotones are also highly variable. They can be be local, extending just a few meters, or they can be regional or even extend hundreds of kilometers. Examples of long distance ecotones include tree lines on mountain ranges and coastal estuaries, which are junctions between saltwater and fresh water habitats.
Ecotones differ from ecoclines in that the latter emphasize a continuous transition in physical or chemical characteristics between two ecosystems, such as in temperature or salinity, rather than sharp transitions, and thus they also have a roughly continuous transition in their composition of species. The species diversity in ecoclines is often greater than that in ecotones because of their gradual nature and because they typically provide more stable environmental conditions than ecotones.