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Green River-Southern Wabash Lowlands

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About the Green River-Southern Wabash Lowlands

The Green River-Southern Wabash Lowlands are a region consisting of two discontinuous pieces: a northern piece in southwestern Indiana, referred to in some documents only as the Southern Wabash Lowlands, and across the Ohio river in Kentucky, a southern piece; this region can be seen as the unglaciated counterpart to the Glaciated Wabash Lowlands to the north.

This region has rolling terrain, with wide, shallow valleys. Although this region was mostly unglaciated, it was indirectly affected by glaciation through the deposition of wind-blown sediment, with sand dunes and wind-blown silt depositions found in the west. The east, on the other hand, has exposed bedrock, mostly sandstone and shale, with some siltstone and coal. Over most of the region, however, the soils are formed on alluvium and lacustrine deposits. The soils here tend to be fine-textured, neutral to acidic, and often high in nutrients. The flat terrain leads this region to be drained by meandering, low-gradient streams and rivers, with wide floodplains and soft substrates. There are an abundance of wetlands and oxbow lakes.

The climate is humid and subtropical, with a long growing season reaching from 175 to over 200 days. Precipitation is weakly bimodal, peaking April-May, with a lower peak in November, and being lowest in January and again in August. For plants, moisture availability is lowest in late summer. Many areas flood seasonally.

This area was originally covered in a mix of oak-hickory forest on drier sites, western mixed mesophytic forest on mesic sites, and southern swamp forests on the wetter sites. Some southern plants reach their northern range limits in this region. Upland sites were dominated by white oak (Quercus alba), post oak (Quercus stellata), southern red oak (Quercus falcata), cherrybark oak (Quercus pagoda), and shingle oak (Quercus imbricaria). Mesic sites were dominated by American beech (Fagus grandifolia), tuliptree (Liriodendron tulipifera), sugar maple (Acer saccharum), and northern red oak (Quercus rubra). Bottomland forests included overcup oak (Quercus lyrata), pin oak (Quercus palustris), silver maple (Acer saccharinum), pecan (Carya illinoinensis), slippery elm (Ulmus rubra), American sweetgum (Liquidambar styraciflua), and red maple (Acer rubrum) on sites that flood only temporarily. Areas with more permanent standing water supported bald cypress (Taxodium distichum).

Nowadays little forest remains, most of it having been cleared for agriculture. This region produces corn, soybeans, wheat, livestock, and assorted vegetables. There are also some oil wells and surface coal mines, mostly in Warrick and Pike counties of Indiana or in the Kentucky part of this region. There is some forest cover, unevenly distributed throughout the region. Much of it in regions where heavily dissected terrain leads to steeper slopes. There are also isolated woodlots of varying sizes and shapes throughout the agricultural regions. There is little public protected land, in spite of this region historically being high in biodiversity. Most of this region is rural and sparsely populated, but two small metro areas, those of Evansville, IN, and Owensboro, KY, although centered outside this region, sprawl out into this area with extensive suburbanization around their peripheries. There are numerous small towns throughout the region. This region is also covered by a dense road network, laid out in a grid on the Indiana side, and more irregular on the Kentucky side.

In the north, this region is bordered to the north by its glaciated counterpart, the Glaciated Wabash Lowlands, which is flatter and covered in highly leached till. To the east lies the Crawford-Mammoth Cave Uplands, which are more rugged, more forested, and have karst topography. To the south and west, this region is surrounded by the Wabash-Ohio Bottomlands, a relatively narrow low-lying region along the Wabash and Ohio rivers and some of their larger tributaries. In the south, this region is mostly surrounded by the more rugged, upland Caseyville Hills to the east, south, and west, and is bordered to the north by the same Wabash-Ohio Bottomlands.

References

1. Woods, A.J, Omernik, J.M., Brockman, C.S., Gerber, T.D., Hosteter, W.D., Azevedo, S.H. "Ecoregions of Indiana and Ohio (Poster)", US Geological Survey (1998) Web.

2. Woods, A.J., Omernik, J.M., Martin, W.H., Pond, G.J., Andrews, W.M., Call, S.M, Comstock, J.A., and Taylor, D.D. "Ecoregions of Kentucky (Poster)", U.S. Geological Survey, Reston, VA (2002) Web.