Indiana Biological Survey
Aquatic Research Center
Division of Fishes Projects
Interior Plateau Ecoregion
Characteristics of the Interior Plateau (IP) Ecoregion are transitional between the adjacent Eastern Corn Belt Plains and Western Allegheny Plateau Ecoregions. The Interior Plateau includes a till plain of low topographic relief formed from Illinoian glacial drift materials, rolling to modestly dissected basin terrain, and rolling to deeply dissected plateaus. Layers of sandstone, siltstone, shale, and limestone underlie much of the Interior Plateau. Limestone outcrops are common, as are areas pitted with limestone sinks.
Approximately 15 percent, or 8400 square miles, of the entire ecoregion is represented on the map of the Upper Midwest. Elevations within this area vary from about 500 feet near the Ohio River, to more than 1000 feet on some of the higher hills. Local relief is commonly between 100 and 200 feet on the till plains and generally around 400 feet in the more hilly terrain, though relief may exceed 800 feet on some of the steeper hills. Average annual precipitation in the Interior Plateau ranges from 40 to 45 inches. Precipitation is distributed fairly evenly throughout the growing season and is usually adequate for crop production.
The majority of the streams in this ecoregion are perennial. Stream density over much of the region is approximately two miles per square mile, except in areas containing numerous limestone sinks, where surface streams are much less common. Large watersheds cover 200 to 500 square miles. Natural lakes are few, and occur mainly in areas underlain by limestone (which may include many limestone sinks containing standing water).
Land use in the Interior Plateau represents a transition between the Eastern Corn Belt Plains and the Western Allegheny Plateau. The Eastern Corn Belt Plains Ecoregion is well suited for cropland and livestock production while the Western Allegheny Plateau is managed mainly for timber and mining products. Acreage in the Interior Plateau is managed for cropland, livestock, pasture, woodland, and forest; the land use varies with local topography. Principal crops include hay, grains, and pasture for livestock. Corn, soybeans, wheat, and tobacco are cultivated to a lesser degree. Beef cattle are the predominant livestock throughout the ecoregion, with dairy cattle and swine well represented. Poultry is raised intensively in some locations. Numerous quarries and gravel pits occur throughout the ecoregion, and some areas are covered by gas and oil fields and coal strip mines.
As with soils of the Western Allegheny Plateau, many of the soils in the Interior Plateau formed in residuum from a variety of sedimentary rocks overlain by varying amounts of loess. Some soils of the Interior Plateau, like those of the Eastern Corn Belt Plains, are derived from calcareous loam till with localized mantlings of loess. Developed under predominantly forest vegetation, soils are lighter in color, more acid, and more likely to have a hardpan layer, Fragiudalfs, Hapludalfs, Fragiudalts, and Hapludults formed on ridge tops , side slopes, and flat areas of uplands. Dystrochrepts, Fluvaquents, and Udifluvents developed in association with floodplains. Fragiaquults evolved in some small basins and depressions, and Haplaquepts in slack water areas. Paleudults developed on old landscapes with broad, smooth slopes.
The vegetation of the Interior Plateau includes a variety of forest types which range from hardwood forests, like those in the Eastern Corn Belt Plains, to mixed mesophytic forest, like that of the Western Allegheny Plateau. The biotic complexity of the Interior Plateau can be attributed to the variety in topographic and edaphic factors. On drier slopes and uplands, forest communities include combinations of oak species (such as white, black, red, scarlet, chinquapin, post, bur, blackjack, and chestnut) and one or more species of hickory (bitternut, mockernut, pignut, and shagbark). Associated trees include yellow poplar, blackgum, sugar maple, red maple, white ash, green ash, American elm, red elm, basswood, sweetgum, and several pine species. Black walnut, black cherry, American beech, and eastern hemlock may also be present. In basins underlain y limestone, forests are comprised of blue ash, white ash, American elm, Ohio buckeye, and red mulberry. Flat areas with impervious soils support maple, white elm, and associated species such as swamp white oak, sourgum, white oak, shellbark hickory, beech, and cottonwood.
Land use impacts on stream quality are mainly from production of livestock, poultry, and crops. Where pastured cattle have access to streams, stream banks become eroded through trampling and removal of riparian vegetation. Manure dispersal can have large effects on stream water chemistry. Many rivers have been channelized and/or dammed for flood control. Such alteration of seasonal hydrologic cycles decreases the array of stream habitats for biota. Strip mines can have long-term physical and chemical effects over many stream miles. Seepage of sludge from drilling sites in gas and oil fields can affect water turbidity and water chemistry.
Indiana Biological Survey - Aquatic Research Center
6440 S. Fairfax Rd., Bloomington, IN 47401
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