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Mississippi Alluvial & Southeast USA Coastal Plains

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Name	†	Color on Map	CEC Code‡
Middle Atlantic Coastal Plain	✓		8.5.1
Mississippi Alluvial Plain	○		8.5.2
Southern Coastal Plain	○		8.5.3
Atlantic Coastal Pine Barrens	○		8.5.4

† 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 Mississippi Alluvial & Southeast USA Coastal Plains

The Mississippi Alluvial & Southeast USA Coastal Plains are a Level II ecoregion extending along the East Coast of the United States from Cape Cod, south through most of Florida, and along the Gulf Coast west to Mid-Louisiana, and extending northward in the Alluvial plain of the Mississippi river.

This region is mostly flatter, lower-lying (under 100m/320ft in elevation, with much of the coastal region being much lower), and warmer than the bordering Southeastern USA Plains. This area is mostly unglaciated except the terminal moraine and glacial outwashes that formed Long Island and Cape Cod. Most of the region is flat. There are extensive wetlands, river deltas, estuaries, and along the coast, barrier islands, beaches, and sand dunes. The soils have more sand, silt, and clay than in the more interior regions.

This region mostly has a humid subtropical climate, milder than in the more interior regions. The northernmost limits of this region have four well-defined seasons and roughly constant precipitation year-round, whereas the southernmost parts have less temperature variation but have a pronounced rainy season arriving in summer contrasting with dry winter and early spring. Although there is some continental influence, the low altitude and proximity to the ocean moderates the climate and diminishes the influence of continental air masses. Precipitation arrives mostly from frontal systems in the cool season and more from convective thunderstorms and hurricanes and other tropical storms in the warm season. Hurricanes are a major force in this area, especially in the southern coastal regions.

Land cover ranges from forest to wetlands to developed land. Wetlands and water are much more common over this region than inland. Pines are more dominant in the coastal areas, reflecting excessively-drained, coarse sands and highly acidic soils. Hardwood forests are more dominant in the more interior floodplains, which have richer alluvial soils.

This area is heavily populated and also heavily utilized for agriculture and forestry, with cropland concentrating along the Mississippi river, and extensive pine forestry in the southeastern coastal plains. The biggest population centers in this region is Houston, TX, and other important ones are New Orleans, LA, Jacksonville, Tampa, and Orlando, FL, and the area around Virginia Beach.

This region is bordered inland by the Southeastern USA Plains, which tends to be hillier, higher in elevation, and better drained than this region. Relative to the southeastern coastal plain, that region also has richer soils, although in the west, it tends to have poorer soils relative to the Mississippi Alluvial Plain. The portion of this region in Florida is bordered to the south by the Everglades, with a humid tropical climate. There is a small border to the west along the Gulf Coast with the Texas-Louisiana Coastal Plain, a flat, marshy coastal area with decreasing rainfall to the West, and habitats that increasingly resemble the Great Plains. The northernmost portion of the Mississippi Alluvial Plain also borders the Ozark, Oauchita-Appalachian Forests to the northwest, an interior region of low mountains.