| Vegetational patterns change across the landscape in response to variation in environmental factors such as climate, soils, and topography. Few studies have assessed the influence of environmental factors on vegetation patterns at the state or regional scale. In this project, I characterized Illinois remnant prairie and determined the major environmental factors correlating with differences in species composition across 216 remnant prairies. I used a data set collected on Illinois remnant prairies in the 1970s. In 1998, I visited 29 of the original sites, resampled the vegetation, and collected soils for analysis. To broaden the data base to a regional scale, I incorporated Wisconsin remnant prairie data collected in the 1950s. Ordination and classification techniques revealed patterns within vegetation and patterns of distributions and abundances of species. Sites separated along a moisture gradient, with a secondary separation by soil texture. I interpreted these gradients by examining site conditions and relating the to ordination score or classification group. Site information collected at the time of the survey and results of soil tests from the resampled sites were used in this interpretation. A Geographic Information System (GIS) was used to model an integrated moisture index for sites. The GIS was also used to interpret the ordination results by examining similarities between ordination score and environmental or geographic parameters, including soil association, size of site, and geographic location of site. Furthermore, species data were linked to the GIS to allow examination of the relationship between ordination score, geographic location, and abundance of selected species for the state as a whole. The major environmental factor affecting species composition of Illinois remnant prairies is moisture availability as a function of topography, with a secondary separation of dry sites based on soil texture. At this scale of analysis, nutrient availability was not important. |