The southern floodplain forest includes bottomland hardwood stands and deep, alluvial swamps. Boundaries are hard to distinguish, but the type is found where streams and rivers occasionally flood beyond their channels and in deepwater swamps that are inundated for most of the growing season. The southern floodplain forest can range in area from broad river floodplains to narrow strips along small stream channels. Many areas are characterized by sloughs, oxbow lakes, and natural levees of coarse material deposited by flooding. In all areas, drying occurs in late summer and early fall.
Soils range in texture from silty clay and clay to sand.
High clay content results in greater phosphorus content. Soils are somewhat acidic, with pH ranges between 5 and 6. Organic matter content is usually 2 to 5 percent higher than in upland soils. High organic matter content accounts for higher nitrogen concentrations and may explain, in part, why bottomland forests tend to be more productive than upland forests. Species composition in southern floodplain forests is a function of constantly shifting factors like stream migration, soil erosion, and deposition, which change the substrate.