Tree Stratum Composition and Distribution in the Streamside Forest

Abstract

The woody vegetation of the streamside forest in Robert Allerton Park, Piatt Co., Illinois, is described in relation to the distribution of river level frequencies of the Sangamon River. The habitats most frequently flooded are dominated by Acer saccharinum. With decreasing flooding frequency, dominance is transferred to Celtis occidentalis and Quercus imbricaria. The areas experiencing no flooding are dominated by Q. alba. Changes in the vegetational structure of elevational increments of .304 m (1 ft) are discussed. The principle that communities change gradually along environmental gradients is illustrated in a vertical elevation of less than 4 m. INTRODUCTION With the current expanding need for water resources, many civil works contractors are rapidly harnessing rivers and streams with a continuing emphasis on the construction of dams and reservoirs. Increased importance is also now being given to the environmental quality of these areas, and this emphasis is expected to intensify in the future. The clash between these seemingly widely opposed philosophies can only be rationally dicussed, and reasonable alternatives suggested, if an understanding of the streamside ecosystem is sufficient to adequately predict the effects of proposed perturbations. Historically, efforts to increase production have received vastly more attention than efforts to measure and mitigate the damaging effects of modern society on our water, land and air resources. As a result, relatively little informations about the effects of dams and similar structures on the dynamics of streamside ecosystems is now available. If ecological changes resulting from water resource development are to be objectively determined, then parameters of the natural biophysical environment must receive added attention. Certainly the riparian forests of the Midwest have come under stress as the industrialization and urbanization of areas within the farm belt have intensified the need for water. Forests within tihe Peninsula section of the Oak-Hickory Forest region described by Braun (1967) are considered to be of three general types: bottomland forests which line most of the streams, upland forests occurring in the upland areas bordering the major rivers and streams, and those isolated timber areas within the prairie, the Prairie Grove forests. The Prairie Grove forests have been considered in some detail by Boggess (1964), Boggess and Bailey (1964) and Boggess and Geis (1966). The upland communities associated with river courses were considered to be older than the Prairie Groves (Boggess and Geis, 1967), as the drainage ways in the Illinois prairie were believed to have been the major migratory pathway for tree in-