Abstract

For three-quarters of a century edge or zone of transition between different ecological associations has intrigued ecologists. high diversity of plants and animals associated with edges and ecotones quickly became known as edge effect principle, which is widely referred to as a fundamental concept of ecology (e.g., Wiens 1976). For 55 years since enunciation as a game management principle, wildlife biologists have considered that the potential density of game of low radius requiring two or more types is, within ordinary limits, proportional to sum of type peripheries (Leopold 1933:132). Standard habitat management guides include prescription to create as much 'edge' as possible because wildlife is a product of places where two habitats meet (Yoakum & Dasmann 1971). But increasing emphasis on plant and nongame wildlife conservation during last two decades has revealed many characteristics of edges and ecotones that are now considered undesirable. term derives from Greek root tonus, referring to tension. As originally coined, referred to zone of tension between ecological communities. As it turns out, term was a harbinger of tension that now exists between scientific communities. Debate about whether land managers should or should not continue to prescribe creation of edges in name of wildlife conservation now simmers in wildlife profession and several land management agencies. This subject was topic of a special session at 1987 annual meeting of Society for Conservation Biology. This introduction and three of five papers presented in that session provided historical and much of contemporary basis for evaluating such land management decisions. As originally formulated, The line that connects points of accumulated or abrupt change ... is a stress line or ecotone (Clements 1907:297). This as well as other early formulations clearly alluded to a onedimensional concept, and ornithologists such as Kendeigh (1944) and Johnston (1947) went so far as to conclude that bird densities should be reported as pairs per 100 acres for forest interior species, but pairs per mile of edge for edge species. Numerous indices aimed at assessing habitat interspersion and/or landscape diversity-for example, shoreline index-are based on this one-dimensional aspect of edge (Welch 1948; Baxter & Wolfe 1972; Scheurholtz 1974; Patten 1974; Fried 1975; Ghiselin 1977; Taylor 1977; Thomas, Maser, & Rodiek 1979; Asherin, Short, & Roelle 1979; Hays, Summers, & Seite 1981). But confusion surrounding nature of edges and ecotones emerged shortly after concept was coined. Shelford (1913) clearly referred to a two-dimensional phenomenon when he stated The forest margin, as we have seen, possesses in addition to characteristic species . .. . and Deventer (1936) treated swamp edge, forest edge, and fence row as though they were discrete habitat types. Johnston (1947) concluded her classic study by stating The forest edge is considered to be a distinct community because it is inhabited by a characteristic set of species.... Beecher's (1942) analysis nearly foretold current forest management quandary when he observed that forest margins only function as edge habitat when their extent is greater than some minimum threshold acreage. Richard Yahner has published extensively on topic of edge effects as they pertain to various groups of wildlife and his paper presented here reviews these various issues as they are understood by practicing wildlife ecologists and managers. Swynnerton was perhaps first to be confronted with intrinsic contradictions of managing for edge ef-

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