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Southern Ozarkian River Bluffs

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About the Southern Ozarkian River Bluffs

The Southern Ozarkian River Bluffs is a narrow region of steep bluffs and ravines, running north-south along the western border of the southernmost portion of Illinois, east of the Mississippi Alluvial Plain. This region is part of a forested corridor along the length of the Mississippi river, and is the most densely-forested of the regions in this corridor.

This region is underlain by cherty limestone that is more resistant to erosion and solution than areas to the north. As such, this region is quite rugged and has only limited karst (caves, sinkholes, and underground drainage), and a greater density of surface streams. Atop the limestone are thick layers of loess, fine-textured wind-blown deposits. Unlike areas to the north, this area was never glaciated. Soils here mostly developed on loess, except on the steeper slopes where the underlying bedrock is exposed and soils developed on a mix of thin loess, leached residuum, and less-eroded pieces of bedrock. These soils are often acidic.

This area was probably originally mostly forested, but little is known about the original forest composition.

Nowadays there is still considerable forest cover here, and the forests are high in plant biodiversity. Topographic variability creating different microclimates, variation in soil acidity, and proximity to numerous different ecoregions all contribute to a high species richness here. Upland forests support numerous oaks, sugar maple (Acer saccharum), bitternut hickory (Carya cordiformis), and American basswood (Tilia americana). Floodplains and bottomlands support American elm (Ulmus americana), eastern cottonwood (Populus deltoides), white oak (Quercus alba), northern red oak (Quercus rubra), American sycamore (Platanus occidentalis), and river birch (Betula nigra). Steep slopes with acidic soils support shortleaf pine (Pinus echinata), which reaches its northeastern limit here, and understories of azalea.

There is some public protected land here, mainly at Trail of Tears State Forest. This region is almost entirely unpopulated, due to its steep topography, and has no towns except the unincorporated community of Diswood, located at the confluence of several of the broadest bottomlands near the southern end of this region. There is only a small amount of scattered rural residential development throughout; much of the area lacks a network of roads, having only a few roads that cut across the region, with roads following the flat valleys of the larger streams. There is also little agriculture, with the little cropland and pastureland limited to the few flatter uplands in the northeastern border of this region, and a few of the broader bottomlands throughout.

This region borders many different regions. The northermost section is bordered to the northwest by the Karstic Northern Ozarkian River Bluffs, a similar region but with less cherty limestone that is more easily eroded, and thus generates more karst. The northernmost section is bordered to the northeast by the Southern Illinoian Till Plain, a flat, higher-elevation region. The border to the southwest and west is with the Middle Mississippi Alluvial Plain, a low, flat region. The borders to the east are variable: in the north, this region has a short border with the Northern Shawnee Hills, and south of that, a longer border with the Southern Shawnee Hills. There is then a short border with the low, flat Wabash-Ohio Bottomlands. The southernmost end of this region is bordered to the south by the low, flat Northern Holocene Meander Belts to the south and the rugged River Hills to the southwest.

References

1. Woods, A.J., Omernik, J.M., Butler, D.R., Ford, J.G., Henley, J.E., Hoagland, B.W., Arndt, D.S., and Moran, B.C. "Ecoregions of Oklahoma (Poster)", Reston, VA, U.S. Geological Survey (2005) Web.