Physical Environment:
Soils

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Illinois prairies developed in a wide variety of soils. The topography and soils at Midewin support many of the major prairie types native to Illinois. Dolomite prairie, one of the rarest prairie types, is present at Drummond Dolomite Prairie on the western side of Midewin National Tallgrass Prairie. Areas of outwash sand near the Kankakee River support a xerophytic (dry loving) sand prairie. Typical of the Grand Prairie, many of the soils of Midewin are poorly drained, supporting wet prairie and marshes.

The soils at Midewin are developed from glacial till, outwash sand, proglacial lake sediments, and dolomite bedrock in the area. Prairie soils (mollisols) are widespread. The surface horizon is thick (at least 10 inches), dark colored, and rich in organic matter. Decomposed roots from prairie sod and charcoal from prairie fires contribute to the color and organic matter. Forest soils (alfisols) are present in the groves and upland forests. The forest litter promotes leaching of organic matter from the surface horizons, which are consequently light colored. These soils indicate a long residence time for the groves or forest vegetation upon them. Prairie-forest transition soils also occur in areas where forest has more recently invaded prairie. Shallow, dolomitic soils occur in Drummond Dolomite Prairie. Sandy soils exist in the outwash areas near the Kankakee. Gravelly, well-drained soils occur in scattered locations.

Soil types at Midewin NTP
Soil types at Midewin NTP

The light pink/orange color that dominates the east side of the map consists largely of poorly-drained silty clay loam developed in glacial till. The red is moderately well drained silt loam, and the bright yellow a poorly-drained silt loam. The southwestern portion of the map is dominated by green. These are thin, poorly drained, silty loam, formed in glacial till over dolomite. The pink colors in the southwestern portion of the map are thin, well- drained silt loam over dolomite bedrock.




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http://www.museum.state.il.us/exhibits/midewin/soils.html, Last modified October 21st 2003, 02:53AM.