East Gulf Coastal Plain
Description & Physiography
The East Gulf Coastal Plain ecoregion encompasses portions of five states (Georgia, Florida, Alabama, Mississippi, and Louisiana) and over 42 million acres from the southwestern portion of Georgia across the Florida Panhandle and west to the southeastern portion of Louisiana. Physically characterized by subtle topography, soils derived primarily from unconsolidated sands, silts, and clays transported to the ecoregion by the weathering of the Appalachian Mountains, the ecoregion has a wide range of land forms. These range from sandhills and rolling longleaf pine-dominated uplands to pine flatwoods and savannas, seepage bogs, bottomland hardwood forests, barrier islands and dune systems, and estuaries.
The Southeast Coastal Plain ecoregions also share other features, including: a high percentage of land area in wetlands, a dominant role of frequent fire over the majority of the landscape, a diversity of river and stream systems, limited but important karst areas, diverse estuarine and tidal systems and significant large scale disturbance events, such as hurricanes.
The area is characterized by a warm to hot, humid, maritime climate.
Plants & Animals
In North America, the East Gulf Coastal Plain ecoregion is one of the true hotspots of biodiversity and endemism. Part of the reason for this is that the ecoregion has never been glaciated, and has been continuously occupied by plants and animals since the Cretaceous, giving ample time for the evolution of narrow endemic species. Many species, particularly vascular plants, reptiles, amphibians, and fishes occur only in this ecoregion, and many of those are even more narrowly limited within the ecoregion.
The dominant ecological drivers of the terrestrial systems are soils (texture and chemistry), fire frequency, and hydrology. Habitats in the East Gulf Coastal Plain include barrier island systems with annual-dominated beaches, maritime grasslands and scrub, maritime shrub hammocks, and evergreen forests (both broadleaf and needleleaf). These grade through salt marshes to productive estuaries. Inland, longleaf pine woodlands are dominant over most of the landscape, on upland and wetland sites and a wide variety of soils. These pinelands (sandhills, clayhills, flatwoods, and savannas) support a tremendous diversity of plant and animal species; most of them specialized to these systems. For instance, the Southeast Outer Coastal Plain as a whole supports about 1,500 endemic vascular plant species, most of them limited to pineland habitats. Embedded in these pinelands, specialized patch communities such as seepage bogs, treeless“savannas” and “prairies”, and seasonally flooded depression ponds provide rich habitat for plants, amphibians, and invertebrates. Imperiled plant species are concentrated in fire-maintained pinelands (wetland and upland), associated seepage bogs and upland depression wetlands, and barrier island communities. While many imperiled animal species also occur in these communities, there are also significant concentrations in aquatic and bottomland systems, as well as in karstlands.
Humans & History
The freshwater aquatic systems of the East Gulf Coastal Plain are among the most significant and at-risk aquatic biodiversity resources in North America, particularly for fish and mussel species (Master et al, 1998). The rivers can generally be categorized into three main groups: brownwater (with headwaters north of the ecoregion and carrying substantial inorganic loads), blackwater (with headwaters in the Coastal Plain and with “coffee-colored” waters dominated by organic acids), and spring-fed (with headwaters in limestone karst). Each of these groups has unique biodiversity resources. Many aquatic animals are endemic to the ecoregion, and many are restricted to a single river system and its tributaries. Thus, conservation of aquatic biodiversity in the East Gulf Coastal Plain requires conservation of most of the river systems. In addition, the East Gulf Coastal Plain supports a range of bottomland hardwood forests and cypress-gum swamps, as well as many lakes and natural ponds.
What is the current status of East Gulf Coastal Plain biodiversity? The pineland ecosystem -- consisting of fire-maintained longleaf pine and slash pine woodlands and their associated seepage bogs and depression wetland -- once dominated a string of ecoregions from southeastern Virginia to eastern Texas. This system has now been reduced to less than five percent of its former range, making it one of the most endangered landscapes in North America. Not only have these pineland ecosystems been directly reduced in extent, but remaining areas are also fragmented and many suffer from the exclusion of fire, a critical ecological process for their maintenance and health. Aquatic systems have been severely affected by hydrologic alterations, pollution, and introduction of non-native species. Most of the hundreds of species endemic to the ecoregion, many of which were never common, have been further imperiled by these changes.