Chicago-area prairies and soil type: Are remnant prairies representative of historical extent?
Land cover change has drastically reduced natural vegetation, especially prairie, in the Chicago area, yet remnant populations of prairie plants remain, often in small patches in the landscape. Remaining prairie in some cases may be the result of historical accident, but in many cases particular lands were likely converted due to their value for agriculture or other human uses. Given that soil type is a key factor for agricultural land use, I hypothesized that remnant prairies would be more likely to be found on soil types less suited for agriculture. To assess this idea, I first evaluated areas recorded as prairie in historical land surveys (from 1820-1840) in the 7 county area around Chicago, and determined soil texture, soil series, and slope of these areas in ArcMap. I then identified remnant prairies within this same area and evaluated the soil and slope for those locations.
Overall, findings indicate that current prairies are fairly representative of historical prairie. However, where there are differences, they suggest that areas less desirable for agriculture were more likely to retain some of their native prairie vegetation. Remnant prairie sites were somewhat more likely to be found on sand soils (5.6% of sites) than might be expected based on the total area of sand soils (1%). Areas with steeper slopes were also slightly over-represented among remnant sites. Although most soil series covered by historical prairie continue to be represented among remnant sites, some series were under-represented, in particular two series that are well drained to moderately well drained. Remnant prairies in the Chicago area, although vastly reduced from historic extent, still represent a wide array of soil environments. However, the communities and the plant genotypes that remain are likely to be associated more with environments deems less suitable for cultivation.