Factors Related to the Distribution of Prairie Plants along a Moisture Gradient

Abstract

Environmental factors influencing the distribution of plant species at Goose Lake Prairie Nature Preserve, Morris, Illinois, were studied. Polar and Gaussian ordination was applied to plant data from 40 stands located along a gentle slope that was 550 m long and varied in elevation only 2.1 m. Selected environmental parameters were measured in each stand. Community types studied varied from drymesic prairie to emergent aquatic vegetation. When species' abundances were plotted over the ordered stands, a series of overlapping curves resulted that generally conformed to species sequences reported by other workers. Stand x-vectors determined by Gaussian ordination were significantly correlated with soil moisture (r = .86, p < 0.01). Application of stepwise multiple regression delineated drainage and elevation and, to a lesser extent, soil depth and texture, as being the environmental variables most important in predicting stand x-vector values and soil moisture. These four environmental variables accounted for 82 % and 84% of the variance in moisture and x-vector values, respectively. INTRODUCTION Except for descriptive studies (e.g., Gleason, 1910; Vestal, 1914; Sampson, 1921; Evers, 1955) little information is available concerning phytosociology of prairie species in Illinois. We expected that plant distributions in response to environmental variation would be similar to those shown by studies of prairies in neighboring states. Studies of Midwestern prairies (e.g., Whitford, 1958; Curtis, 1955, 1959; Dix and Butler, 1960; Partch, 1962; Bliss and Cox, 1964; Dix and Smeins, 1967; Redmann, 1972; Crist and Glenn-Lewin, 1978) demonstrated a gradual change in species composition in response to a topographic gradient. However, at Goose Lake Prairie Nature Preserve plants generally thought to be dissimilar in their habitat preferences, based on these studies, were often found growing in close proximity without any obvious differences in their habitats. Therefore a study was initiated in 1977 to determine distributional patterns of major plant species at Goose Lake Prairie and to relate these patterns to environmental conditions. Studies that examined environmental factors influencing plant distribution in prairie vegetation similar to that of Goose Lake Prairie revealed that plant compositional changes in response to elevation were due to the presence of moisture gradients (Dix and Smeins, 1967; Hulett et al., 1968; Whitman and Wali, 1976; Clambey and Landers, 1978). For example, Dix and Smeins (1967) found that drainage, influenced by topographic variation, determined the pattern of prairie, meadow and marsh vegetation in North Dakota. Similarly, topographically caused variation in water depth and permanency were primary factors determining plant community structure in Iowa wetland vegetation types (Clambey and Landers, 1978). STUDY AREA The 612-ha Goose Lake Prairie Nature Preserve (4 km long by 2.4 km wide) is located 10 km E of Morris, Grundy Co., Illinois. Topography is flat to gently rolling and, except for a few areas, changes in elevation are subtle. Total relief is only 11 m and slopes greater than 5 % are rare. Soil depth to bedrock varies from 20-150 cm. The preserve is poorly drained and extensive areas of standing water are common after heavy or frequent storms.