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Bluff Hills

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About the Bluff Hills

The Bluff Hills are a collection of discontinuous areas where there is steep, rugged terrain covered in thick deposits of loess. The region is mostly located east of the Mississippi river, towards the west end of the Mississippi Valley Loess Plains, extending from Kentucky through Tennessee and well into Mississippi, but there are a few small discontinuous pieces west of the river in Missouri and Arkansas as well.

This region consists of steep, highly-dissected terrain, including steep hills, bluffs, winding ridges, and narrow valleys. This region is mostly covered in thick layers of loess, but the steep topography has caused lower layers to be exposed as well; there are some unconsolidated sandy and gravely sediments, and along the western bluffs in the eastern sections of this region, some areas of exposed sand, silt, and clay. Soils tend to be deep, well-drained to excessively-drained, nutrient-rich, and erosion-prone. The portions of this region in Missouri and Arkansas have a greater portion of sandy or gravely soils, which are more drought-prone and lower in fertility; this area also has more spring-fed streams and seeps.

The climate is humid and subtropical, but this region covers such a large area that there are substantial climate differences over its range. Winter lows average as much as 12°F (7°C) lower in the north than the south, with daytime highs varying even more, by as much as 16°F (9°C); summer temperatures are only slightly warmer in the south, differing by about 3°F (1.5°C). The growing season ranges from 180 degrees in the north to 250 days in the south, with a weak seasonality that varies regionally. The north has a bimodal precipitation pattern, peaking in late April and again in late November, with a dry season peaking in August; in the south, rainfall is consistently higher in winter with summers having less rain but more cloud cover. The western portions of this region also have slightly lower rainfall. The northern and western portions of this region also have more continental influence to the climate, experiencing more extreme swings of temperature and humidity.

This region was mostly forested originally; because it spans such a large area, forest cover varies considerably throughout. In the north, drier uplands supported oak-hickory and mixed oak forests, mostly dominated by white oak (Quercus alba). More mesic slopes supported sugar maple (Acer saccharum), bitternut hickory (Carya cordiformis), tuliptree (Liriodendron tulipifera), and American beech (Fagus grandifolia). In the south, more mesic sites featured water oak (Quercus nigra), cherrybark oak (Quercus pagoda), white oak, American sweetgum (Liquidambar styraciflua), American basswood (Tilia americana), tuliptree, beech, and white ash (Fraxinus americana). At the very far southern end, from Vicksburg, MS onward, there was also some beech-magnolia-holly forest, with beech, southern magnolia (Magnolia grandiflora), and American holly (Ilex opaca) as dominants.

The separate pieces in Missouri and Arkansas had a slightly different forest composition, with fire-prone, open forests of blackjack oak (Quercus marilandica) and post oak (Quercus stellata) on the driest sites, southern red oak (Quercus falcata) and white oak on the slightly less dry sites, and beech and sugar maple on the more mesic sites. On sandy soils, there is also a small amount of shortleaf pine (Pinus echinata), mainly in northern Arkansas. Tuliptree is found on disturbed or early-successional sites.

Currently this region is still largely forested, with a similar composition to the historical cover, but there is some pasture and cropland, mostly on the gentler slopes. The region produces livestock, hay, corn, soybeans, and wheat, and in the south, cotton. The portions in Arkansas and Missouri have drier and less-fertile soil and are mostly used for pasture, with little cropland, but in Arkansas, peaches are also produced here. There is also some oil and gas extraction in Mississippi. This region is sparsely populated throughout. It contains only small towns, many of which are unincorporated, and some of the sparser, outer reaches of Memphis' suburbs. For the most part, towns tend to be built mostly on the lower, flatter areas just outside of this region.

The eastern portions of this region are mostly bordered to the east by the Loess Plains, which are flatter and have little exposed bedrock. In the far south in Mississippi, this region is instead bordered to the east by the Southern Rolling Plains. To the west, these portions of the region are bordered by various regions of the Mississippi Alluvial Plain, mostly by the Northern Holocene Meander Belts, except for areas where they instead border the Northern Pleistocene Valley Trains, and a few areas where they border the Northern Backswamps.

The western portions of this region are entirely surrounded by the Mississippi Alluvial Plain, and is bordered to the east mostly by the St. Francis Lowlands, except in the south of the Arkansas portion where it is bordered by the Northern Holocene Meander Belts. These portions are all bordered to the west by the Western Lowlands Pleistocene Valley Trains.

References

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. Griffith, G.E.; Omernik, J.M.; and Azevedo, S.H. "Ecoregions of Tennessee (Poster)", U.S. Geological Survey, Reston, VA (1998) Web.