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Outer Bluegrass

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About the Outer Bluegrass

The Outer Bluegrass region, sometimes referred to as the Northern Bluegrass region, is an irregularly-circular area stretching from southwestern Ohio into northern Kentucky.

This region is underlain by a mix of limestone and shale, and consists of rolling hills with karst topography, featuring sinkholes, springs, and entrenched rivers. There are both perennial and intermittent streams. The northernmost parts of this region have discontinuous glacial till from pre-Wisconsinian glaciations; this till is highly leached and produces acidic, nutrient-poor soils, contrasting with most of this region which has fertile, calcium-rich soils.

This region has a humid subtropical climate with a mild seasonality of precipitation, the wetter season peaking in May and the drier season peaking in September.

The original vegetation of this area is poorly understood. At the time of European settlement, uplands were dominated by open savannas, with stands of open white oak forest on more acidic sites. However, there is evidence that these trees are remnants of a closed-canopy forest which was cleared by Europeans at the time of settlement. The forest may have been a relatively short-lived phenomenon driven by Native American population loss caused by diseases brought to North America by Europeans. Prior to this, Native Americans probably maintained this area as grasslands over a much longer time-scale. However, the climate and soil type is sufficient to support closed-canopy forests, which probably would have covered the area were it not for human intervention. Forest cover was probably Oak-Hickory forest, with some western mixed mesophytic forest in the northern portions of this region in Ohio and Indiana, and some mixed oak and oak-sugar maple in Ohio. The region along the Ohio river featured bottomland hardwoods. There was also a lot of giant cane (Arundinaria gigantea) along streams, especially in the east.

Current land usage is mostly agricultural, with some urban development. Agriculture is much more diversified than regions farther north, and includes general farming, dairy farming, pastureland, hay, corn, soybean, small grain, and tobacco production. Remaining forest cover is sparse in the south, but much higher in the north of this region, where there are larger tracts of forest, and some public lands including Miami Whitewater Forest and the smaller Mitchell Memorial Forest, Shawnee Lookout, and Mt. Airy Forest. In the south, even small woodlots are rare, and forest cover is mostly limited to long, narrow strips of forest along streams. This region is quite populous, including most of the Cincinnati, OH and Louisville, KY metropolitan areas. This region has poor water quality owing to runoff from agriculture and urban areas.

This region surrounds the Hills of the Bluegrass, but in the east, it also directly borders the Inner Bluegrass to the west. To the east, there is an abrupt border with the much more rugged Knobs-Lower Scioto Dissected Plateau. To the north and northwest there is a border in most places with the highly-leached Pre-Wisconsinan Drift Plains, although in a few places there is a direct border with the more recently-glaciated and agriculturally-fertile Loamy High Lime Till Plains. Along the Whitewater River in Indiana, there is also a small border to the north with the Whitewater Interlobate Area. To the south and southwest, this region borders the Knobs-Norman Upland.


1. 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.

2. 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.