. Comprehensive plan for the Illinois Nature Preserves System. Nature conservation; Wilderness areas. 7 WESTERN FOREST-PRAIRIE DIVISION The Western Forest- Prairie Division is a strong ly dissected glacial till plain of Illinoian and Kansan age. At the time of settlement, forest was the pre- dominant vegetation, but there was also con- siderable prairie on the level uplands. The prairie soils were devel- oped from loess and are fertile. The two sections are geographically separated by the Illinois River valley also have some faunal diffe GLACIAL HISTORY Most of the bedrock is covered by glacia
. Comprehensive plan for the Illinois Nature Preserves System. Nature conservation; Wilderness areas. 7 WESTERN FOREST-PRAIRIE DIVISION The Western Forest- Prairie Division is a strong ly dissected glacial till plain of Illinoian and Kansan age. At the time of settlement, forest was the pre- dominant vegetation, but there was also con- siderable prairie on the level uplands. The prairie soils were devel- oped from loess and are fertile. The two sections are geographically separated by the Illinois River valley also have some faunal diffe GLACIAL HISTORY Most of the bedrock is covered by glacial drift from the Illinoian stage of Pleistocene glaciation. There is an area of older Kansan drift in the west- em parts of Pike and Adams counties. BEDROCK Pennsylvanian and Mississippian bedrocks of limestone, sandstone, shale, and coal crop out frequently along the major streams. TOPOGRAPHY The till plain is strongly dissected, with many ravines in the level to rolling uplands. Flood- plains are developed along the major streams. SOILS Most of the soils are fairly young, having de- veloped from four to five feet of loess. The prai- rie soils are high in organic matter and are simi- lar to those of the Grand Prairie Division. The forest soils are acidic and low in organic matter. Relatively small areas of droughty, fine-textured soils have developed in till on some steep slopes. PLANT COMMUNITIES FOREST: The upland forests consist of an oak-hickory association with black oak, white oak, and several species of hickory as the domi- nants. Scattered sites of fine-textured soils sup- port a post oak-blackjack oak community. This forest community also occurred on the margins of the prairies, perhaps because of fires. The mesic forests contain white oak, red oak, basswood. sugar maple, and slippery elm. The floodplain forests are dominated by silver maple, American elm, ashes, and box elder. PRAIRIE: In presettlement times large prai- ries existed on the uplands of this division. C
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