Alabama Landscapes

The Coastal Plain

Coastal Plain Soils, Agriculture and Vegetation

Soils and Agriculture

Three major soils occur in the Coastal Plain

The soils throughout most of the Coastal Plain are characterized by a well-developed clay horizon underlying a humus-poor topsoil, typical of the Ultisols.  Depending on the underlying material (sandstone, sand, silt or clay) they have a sandy or loamy surface layer and a loamy or clayey subsoil.  This grouping includes Bama Soil, the state soil of Alabama.

Figure CPSV1.  Soil developed on residuum, Dougherty Plain.  Near Red Ridge, Covington County.  The B horizon is clay-rich. (Image © Mike Neilson)

Soils developed mainly on the chalks of the lower Selma Group (Mooreville and Demopolis Chalk) of the Black Prairie are distinctly different from those in the other areas of the Coastal Plain.  The soils are clay-rich, maybe acid or alkaline depending on the parent material,   The alkaline soils are clayey throughout and have a dark-colored, organic-rich surface layer and a yellow to brown colored subsoil (Vertisols). Much of the clay shrinks and swells excessively as it dries or becomes moist and cracks are common in drier periods.  Along the boundary with the Southern Pine Hills, the soils are acid and poorly-drained,

The soils are mainly used for timber, pasture and soybeans. Despite its history of cotton production, the Black Prairie is now a minor producer of that crop.

 Along the floodplains of the major rivers (see Figure CPR3 for locations), immature Inceptisol soils with little horizon development occur.  Formed from flood deposits, they are generally brown in color and clay or silt-rich

About 28% of this land is used for crops and pasture.  Peanuts are a major crop on the Dougherty Plain (southeast  Alabama) and Baldwin County is a major producer of soybeans and pecans.  Cotton is also a major crop along the southern tier of counties.  Beef cattle production dominates pastures. 

Vegetation

The Coastal Plain has four major forest associations (Figure CPSV2)

Figure CPSV2. Forest types in the Coastal Plain.  Black circles: N-Montgomery, S-Mobile. (Simplified from http://www.forestry.auburn.edu/fpdc/alforest.html)

Most of the Coastal Plain is covered with thick stands of loblolly and shortleaf pines.  Much of this is regrowth after timber and pulpwood operations (Figure CPSV3). 

Figure CPSV3. Timber “farm” with several generations of pine trees. South of Georgiana, Butler County (Image © Mike Neilson)

Oak-pine vegetation occurs in the higher regions of the Southern Red Hills and along the Chattahoochee River valley.  The southwestern region (Lime Hills, western part of the Dougherty Plain and the Southern Pine Hills) is covered by oak-hickory stands, which are the sources of much of the timber industry.  Along the floodplains of the Tombigbee and Black Warrior Rivers and south along the Alabama River to Mobile, a rich Oak-Gum-Cypress forest has developed (Figure CPSV4).

 Figure CPSV4.  Cypress swamp near Delchamps, Mobile County (Image © Mike Neilson)

The Black Prairie, (shown as the central white area on the  map) has a distinctive vegetation.  In places, it is bare or covered with short grasses (Figure CPSV5), and was described by scientists in the 19th century as a “prairie.”  Hardwoods dominate in the lower elevations.  One early visitor described the “forests of stately trees.”  Oaks, sweetgums, sycamores, and cottonwoods are common.  Because of the calcium-rich soils, cedars are also common.  In 1913, it was estimated that hardwoods made up about 80% of the tree species in the Black Prairie.

Figure CPSV5.  Black Prairie, SE Montgomery H-231. (Image © Mike Neilson)

On the Dougherty Plain in the southeastern part of the state has developed “a park-like growth of long-leaf pine,” with little undergrowth (Figure CPSV6). The undergrowth is mainly wiregrass, a small spiky to wiry grass (Figure CPSV7).  Its abundance along the Alabama-Florida-Georgia border led to that area being called the Wiregrass region.

Figure CPSV6.  Longleaf Pine, near Geneva, Geneva County.  Long leaf pines have needles 8-18" long and cones that are up to 12" in length.  (Image © Mike Neilson)

Figure CPSV7.  Wiregrass, Houston County.  Wiregrass is often the ground cover for longleaf pine forests.  Periodic burning of the grass regenerates the forest.  (Image © Mike Neilson)

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