Flucutations in Biotic Communities I. Prairie‐Forest Ecotone of Central Illinois

Abstract

The ecotone between deciduous forest and prairie is a tension zone which, by virtue of biotic forces, growth forms, and mores characters, results in a very unstable condition with dynamic annual, seasonal, and diurnal fluctuations in the biota. Although of composite character, the emergent result is, in some degree, a totally new community characterized by a different biota, or a somewhat changed or modified mores on the part of the constituent biota usually considered characteristic of either or both of the adjoining biomes (Bird, '30, p. 362). The entire tension area may be termed ecotone of the first order to distinguish it from the ecotone of the second order which is composed of forest edge thickets of individual forested plots in the larger tension zone. Plant studies in areas of this type have been made in various areas by Weaver and Himmel ('17), Pool, Weaver, and Jean ('18), Vestal ('18), Hanson ('22), and Clements and Weaver ('24). Biotic study of such areas has remained untouched. As has been pointed out by Shelford ('13) and Weese ('24) this area has its own fauna which ranges into the adjacent grassland and forest comnmunities; certain plants likewise have an overlapping zone of distribution in the second order ecotone. There is an environmental gradient within which, for the animals at least, exist a variety of micro-climates. Hence the entire biota is essentially a composite of forms of adjoining communities, but also includes indigeneous forms which often form an important part of the perennial nucleus. The area studied was in the ecotone parkland and savannah area of Illinois. Patches of woods and outlying thickets in the area originally occupied by the river forest of the Salt Fork of the Vermillion river in the vicinity of Urbana, Champaign County, Illinois, were selected as being representative relics of former wide spread communities. The woodlands selected are known locally as the Brownfield Woods (sec. 1, T 19 N, R 9 E) and the University Woods (sec. 34, T 20 N, R 9 E) and previously have been studied by McDougall ('22, '25, and '28), Weese ('24), Telford ('26), Blake ('27 and '31), and Smith-Davidson ('28, '30, and '32). Prairie communities nearby have been studied by Shackleford ('29) and Rice ('31). The forest border of thicket and brush in its original undisturbed condition occupied a width of approximately .004 miles. In northern and central Illinois this probably totaled one per cent of the total area.