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Southeastern USA Plains

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Name	†	Color on Map	CEC Code‡
East Central Texas Plains	✓		8.3.8
South Central Plains (Piney Woods)	○		8.3.7
Piedmont	○		8.3.4
Northern Piedmont	○		8.3.1
Southeastern Plains	○		8.3.5
Interior Plateau	○		8.3.3
Interior River Valleys and Hills	○		8.3.2
Mississippi Valley Loess Plains	○		8.3.6

† Status: ✓ = Complete ○ = Needs Image … = Incomplete ∅ = Stub Only

‡ This code refers to the CEC's Level 3 ecoregion codes for North America, see here.

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↑About the Southeastern USA Plains

The Southeastern USA Plains is a region of the Eastern Temperate Forests, and the largest level II ecoregion in the eastern U.S. It consists of two discontinuous pieces, a small one West of the Mississippi in eastern Texas, southwestern Arkansas, and northwestern Louisiana, and most of the region east of the Mississippi, extending north into Illinois and following a U-shape on the map, northeast along the east coast to Pennsylvania and New Jersey, wedged between the Appalachian mountains and the coastal plain.

The topography over much of this region ranges from relatively flat to rolling hills. There is more topographical variation than in the coastal areas to the southeast or the Mississippi Alluvial Plain, but less than in the Appalachians. This region is mostly unglaciated, except for a few small areas at its northernmost limits.

The climate is humid and subtropical with continental influences, with most of the region lying towards the colder end of subtropical. There are four seasons, well-defined in the north but becoming less pronounced as one moves south. The absence of tall mountain ranges creates a continental character to the climate, meaning that there can be large day-to-day or week-to-week swings in temperature and humidity, as chaotic dynamics arise from the interaction of warm air from the gulf of Mexico, cold air from Canada, and cooler, humid air coming off the Atlantic ocean, or drier air coming from the interior west. Although this region averages moderate levels of precipitation year-round, prolonged period of drought or flooding, as well as long cold or warm spells are possible at any time of year.

Much of this region was historically dominated by hardwood forests, although there are mixed and coniferous forests in part of it as well, with pines becoming more common in the southern parts, and there are scattered areas of savanna and prairie, especially in the western and southern portions. Contrasting with more northerly and interior regions, broadleaf evergreen trees and shrubs are common in most of this region, although not usually dominant. There are significant wetlands, but less than in the flatter areas of the Mississippi alluvial and coastal plain regions.

Current land use patterns make this area a patchwork of forest, agricultural land, and urban and suburban development. Prairies and savannas have been greatly reduced in extent, both due to agricultural development that tended to focus on prairie-dominated areas, and fire suppression that has led some of these areas to convert to forest.

This region shares a large border with the Mississippi Alluvial & Southeast USA Coastal Plains; it borders the Mississippi Alluvial region both to the east and west, and is bordered by a small coastal plain along the gulf coast, and a larger plain to the southeast along the east coast. Inland, it is bordered by the more mountainous Ozark, Oauchita-Appalachian Forests. The interior portion shares a border to the north with the Central USA Plains, and the northwest with the Temperate Prairies.

This region is heavily populated, containing most of the metropolitan areas of Washington, D.C., Baltimore, MD, Atlanta, GA, Nashville, TN, most of the Philadelphia, PA metro area, and a small part of New York City's metro area. This region is also moderately utilized for agriculture, both cropland and pastures, and heavily used for forestry, especially in the southern parts of its range. This region is high in biodiversity, but faces serious threats from habitat loss and also introduction of invasive plants through horticulture.