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Northern Hilly Gulf Coastal Plain

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About the Northern Hilly Gulf Coastal Plain

The Northern Hilly Gulf Coastal Plain, referred to in some documents as the Southeastern Plains and Hills, is a region of the Southeastern Plains located in western Tennessee and northern Mississippi. The southern end of the region, in Mississippi, is separated into a narrower eastern portion and a broader western portion. This region consists of bands of sand and clay formations with north-south orientations.

This region consists of dissected, irregular plains, low, broad-topped hills, and broad bottomlands along streams with level to gently undulating terraces. The region is underlain by a mix of different substrates of varying texture, mostly sands and gravels. These include iron-rich sands, other coarser sands, clayey fine sands, clay, silty clay, and clay decomposition residuum, chert-pebble gravel and sand, some loess and lignite (brown coal), and in the southeast, some sandy limestone. Soil types and textures are highly variable, ranging from well-drained to poorly-drained, and highly fertile to leached and highly infertile, but on average, this region contains more soils low in fertility.

The climate is humid and subtropical with a weakly seasonal precipitation pattern. A wet season peaks in late April, and precipitation declines to a low in late August, then increasing to peak again in early December. The drier season brings both lower rainfall and higher sunlight, but humidity usually remains high. Although total rainfall is high, the dry season is pronounced enough to impose significant drought stress on plants, especially those growing on drier soils and sunnier exposures.

Original forest cover here was diverse. The north of the area was mostly covered in oak-hickory and oak-hickory-pine forest, with bottomland hardwoods along streams and rivers, including American sycamore (Platanus occidentalis), American sweetgum (Liquidambar styraciflua), and tupelo (Nyssa sp.). In the south, mixed oak and oak-pine forest was more common. Dominant trees included black oak (Quercus velutina), post oak (Quercus stellata), blackjack oak (Quercus marilandica), southern red oak (Quercus falcata), southern red oak (Quercus falcata), pignut hickory (Carya glabra), mockernut hickory (Carya tomentosa), and some shortleaf pine (Pinus echinata). More mesic sites supported white oak (Quercus alba), sweetgum, American holly (Ilex opaca), American beech (Fagus grandifolia), and tuliptree (Liriodendron tulipifera).

Nowadays there is a mix of land use. In the north there is mostly wild forest interspersed with pasture and cropland producing hay, soybeans, corn, sorghum, wheat, and cotton. In the south there is a bit less cropland but there are also some pine plantations, and there is some public protected land, most notably Holly Springs National Forest. There is some urbanization here, with the region containing the small cities of Jackson, TN and Oxford, MS, as well as many smaller towns. Most of the region, however, is sparsely populated.

This region is bordered to the west by the Loess Plains, a heavily agricultural region with fine-textured soils. In the north, this region is bordered to the east by the Western Highland Rim; just south of that there is a small border to the east with the Transition Hills, and south of that, with the Fall Line Hills. In the south of this region, where it is divided, the eastern portion is bordered to the east by the Blackland Prairie. The two sections are separated by a long area of Flatwoods/Blackland Prairie Margins. The westernmost section is bordered to the south by the Southern Hilly Gulf Coastal Plain.

References

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