Interior Low Plateau Ecoregion

Description & Physiography

Often, the key factor in describing land physiography is how it fared during the ice age. The geology of the Interior Low Plateau is of two primary types: the Glaciated Illinoian till that dominates the landscape on the northern edges in Ohio and Indiana, and over much of Illinois, and, to the south, an unglaciated portion of rolling limestone plains punctuated with regions of fairly rugged hills with areas of swampy alluvial valleys, deeply entrenched rivers and streams, and expansive karst plains. Several large rivers traverse the ecoregion, including the Ohio, Tennessee, Cumberland Kentucky and Licking Rivers. All in all, the ecoregion occupies portions of six states in the Midwest and South East regions of the United States, Illinois, Indiana, Ohio, Kentucky, Tennessee and Alabama. Compared with other ecoregions, it is of average size, covering over 74,000 square miles.



The mean annual precipitation across the area sub-regions ranges from 44 to 55 inches, with total rainfall a bit higher in Illinois than in Kentucky and Indiana. The average annual temperature ranges from 57 F in Illinois to 55 F in Kentucky and southern Indiana.  Frost free days average about 190 in Illinois and 185 in Indiana. The growing season lasts 180 to 205 days.


Plants & Animals

Forests in the Interior Low Plateau tend to be transitional between the Mixed Mesophytic Forests to the east in the the Cumberland Plateau and Mountains and the Oak-Hickory forest found to the north and west.  Slope forests feature American beech, sugar maple, yellow-poplar, white oak, white ash, northern red oak, black oak, Shumard oak, blackgum, pignut hickory, and other oaks and hickories. Dry sites on west or south facing slopes are predominately chestnut oak, and other dry site oaks, and hickories. (

Over 150 bird species nest ( in the Interior Low Plateaus physiographic area and the primary game animals and furbearers of the region are the white-tailed deer, gray fox, red fox, raccoon, opossum, striped skunk, mink, muskrat, eastern cottontail, fox squirrel, and gray squirrel.

The paddlefish and sturgeon have been greatly impeded from their migration in these waters by locks, dams, and impoundments along the Ohio River and its major tributaries. Other fauna in these waters are common throughout the State. Uniquely noticeable mussel fauna within this Section are the elktoe, snuffbox, rabbitsboot, and salamander mussels. Populations and habitat being hindered by impoundments.


Humans & History

Prehistoric Native American activities had little effect on the Interior Low Plateau. After 1800, however, approximately 50 percent of the landscape was cleared and most wetlands drained by Euro-Americans. Fires became more frequent during this period, as did erosion, since the hillslopes had been denuded for timber and fuel. Today, the landscape is a patchwork of forest and agricultural lands, the former used for recreation, ecosystem maintenance, and wood-fiber production, the latter for grazing and row crops. Energy and mineral production have affected small portions of the landscape; coal, iron, lead, zinc, fluorite, limestone, sand, and gravel have been mined in the Section, beginning in the mid-1800's. Oil and gas production began in the early 1900's. (



Habitat loss to agriculture and other uses and the fragmentation and reduced quality of what remains are the biggest conservation issues in this area. Grasslands and savannahs have been converted to cool season pasture. Many glades and barrens have become urban areas, and others have been overtaken by woody vegetation due to fire suppression. Especially, in the unglaciated portion of the ecoregion, forests still cover approximately 41% of the landscape. While much of this forest is fragmented, extensive areas of contiguous forest (>300,000 acres) persist in Tennessee, eastern Kentucky, and central Indiana and serve as biodiversity reservoirs for area sensitive species, especially interior breeding neotropical migrant birds.

The Central Tillplains Section has faired less well. The flat terrain and till-derived soils have been especially hard hit, and only small ecosystem remnants persist today - conversion to row-crop agriculture has been almost complete. In Ohio and Indiana, the tillplain portions of the glaciated portion of the Bluegrass Section has fared slightly better, but even so, ecosystem remnants are highly fragmented.

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