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Western Dissected Illinoian Till Plain

Ecoregion in IL

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The Western Dissected Illinoian Till Plain ecoregion is a well dissected, pre-Wisconsinan till plain with broad, nearly level interfluves, and many forested slopes, ravines, and floodplains. It is generally more dissected and forested than the Illinois/Indiana Prairies (54a), and is physiographically distinct from the broad flats and hills of the Southern Illinoian Till Plain (72j). The Western Dissected Illinoian Till Plain (72i) is capped with loess and till, and is underlain by Pennsylvanian and Mississippian limestone, sandstone, shale, and coal; outcrops are common in valleys and ravines (Schwegman, 1973, p. 19). Alfisols are common, and are low in organic matter, acidic, and well-drained. Mollisols also occur, but are less extensive than in Ecoregion 54a; they developed in thick loess (Natural Resources Conservation Service, various dates). In the early 19th century, oak – hickory forests covered well-drained slopes, whereas more mesic sites supported white oak, red oak, and basswood (Schwegman, 1973, p. 19). Prairies were found on nearly level interfluves (Nelson, 1978, p. 104). Marshes and wet prairie also occurred, but were less common than in the Central Corn Belt Plains (54). Today, cropland and pastureland have almost entirely replaced the native prairies; corn and soybeans are the main crops. Steep slopes and ravines remain largely wooded, but forested acreage is less than it was at the time of settlement. Artificial drainage is less extensive than in neighboring Ecoregions 54a; partially as a result, nitrate concentrations in the surface waters of The Western Dissected Illinoian Till Plain ecoregion tend to be lower than in Ecoregion 54a (personal communication, 2005, Charles Pederson). Sheet erosion can be severe on cultivated slopes.

— EPA

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Western Dissected Illinoian Till Plain

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