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Identifying Differences in Illinois Dry Prairies by Examining Soil Factors and their Effects on Plant Species Composition

Lundgren, Jessie. 2013. Texas A&M


Illinois is home to a wide array of prairie remnants that have been preserved from the period of westward expansion. Of these, dry prairies are known to be among the most species rich. Within the class of dry prairies there are three major types in Illinois: dolomite prairies, gravel hill prairies, and sand prairies. For years these prairies have only been differentiated by their substrate as each of their names imply, but no work has been done to confirm whether or not the substrate does differ significantly, and if that difference alters the environment enough to change the plant community. This study was conducted to deepen the understanding of the factors setting these prairie types apart. To accomplish this 18 remnant prairies representing a mixture of the three site types were examined. At each of these locations soil properties were analyzed including nutrient availability, infiltration rates, and soil texture. In addition, a survey was performed to determine plant composition at each study site. Soil nutrients differed among the different prairie types, with significant differences between sand prairies, and dolomite and gravel prairies. These differences were most evident in nitrogen, potassium, magnesium, and calcium. Other important nutrients such as phosphorous, iron, and copper were not significantly different between all three types. Infiltration rate was not significantly different between sand and either of the two other site types, but dolomite and gravel hills varied significantly from each other. Soil texture was also found to vary significantly between dolomite and the other two site types with much higher proportions of clay and silt in dolomite prairies. The plant surveys were analyzed in R using an ordination to graphically display the plant species as they relate to the three prairie types. The results of this analysis suggest there is a significant difference in floral community of sand prairies compared to the other two prairie types, whereas gravel hill and dolomite prairies do not differ significantly from each other based on the plant community. This research suggests there are some significant differences between the soils of these prairies, and there is a significant difference in species composition which can also differentiate these sites from each other. Additionally, gravel hill and dolomite prairies may not be two distinct types of prairies based on their species composition and soil properties. Considering these two prairie types as a single type instead would allow management agencies to use time and resources more effectively by managing these sites together.