Upper East Gulf Coastal Plain Ecoregion
Description & Physiography
Encompassing some 52,908 square miles, the Upper East Gulf Coastal Plain has been worked and reworked by coastal and fluvial processes – and sculpted by wind-deposited silt called loess. Bluffs along the eastern edge of the Mississippi River, such as those around Vicksburg, are covered with up to 200 feet of loess. Approximately 70 million years ago, the ecoregion would have been around 4000 ft elevation. However, the earth’s crust later sagged forming a trough called the Mississippi Embayment. During the Tertiary and Cretaceous periods this trough was repeatedly invaded by shallow seas which left behind 100’s of meters of sediments that occupy broad bands approximately paralleling the Gulf of Mexico, which give satellite imagery its belted character.
More recently, in 1811, the New Madrid earthquake revealed an ancient, buried rift zone, which has acted as a “zone of weakness” in the continental crust. The quake was among the strongest in recorded United States history, resulting in 9 feet of land subsidence in the region around Reelfoot Lake in Tennessee.
Generally, the Upper East Gulf Coastal Plain features a warm to hot, humid maritime climate, though the cool ravines of the Tunica Hills have produced a micro-climate, home to plants and animals typically found in northerly regions such as the Ozarks and Appalachian Mountains.
Plants & Animals
The vast majority of the Upper East Gulf Coastal Plain has been considered a “Priority Class 1” for freshwater species conservation due to the richness of the fauna present. For example, rivers in this region provide habitat for over 206 native fish species; making the region among the top 3 in the southeastern United States. This species richness may be due, in part, to the fact that the Mississippi Embayment region was an important refugium for fish diversity during Pleistocene glaciation. The region also supports relatively large numbers of crayfish and mussel species despite heavily disturbed conditions, especially the Mississippi tributaries, that have been channelized or subjected to heavy sedimentation.
The natural vegetation of the Upper East Gulf may be characterized as broad bands of different composition that roughly parallel the coast. From south to north these include southern mixed forests, oak-hickory-pine forests, and oak-hickory forests, interrupted by occasional southern floodplain forests and black belt prairies. The two predominant forest types – southern mixed forests and oak-hickory-pine forests – include large amounts of longleaf pine (Pinus palustris) and shortleaf pine (Pinus echinata) respectively.
Humans & History
Much of the Upper East Coastal Plain features agriculturally productive soils and were among the South's most important agricultural areas before the American Civil War. The long history of cultivation and disturbance has left few large, intact prairies in the region. Likewise, extensive ridge-top clearing took place between the early 1820's and mid-century. Eventually few forested ridges remained, and many native plants and animals disappeared from all but the steep slopes and deep ravines. Louisiana’s Tunica Hills became an important agricultural center, and many of the popular trading routes used to haul agricultural products to the steamboat docks along the Mississippi River are visible today. After the Civil War, many plantations in the region were abandoned, and natural succession resulted in the forests we see today.
Today, Upper East Coastal Plain areas, such as the Tunica Hills in Louisiana, are dominated by many of the same species recorded by the early land surveyors, with a few notable exceptions. Here, Loblolly pine, which was never noted during the surveys and is thought to have occurred no further west than the area around Thompson Creek, is now very common. Loblolly pine seeds are readily dispersed by the wind and animals, and the species rapidly colonizes abandoned fields. Finally, exotic species, most notably Japanese privet, which likely escaped from ornamental plantings around the original plantations, have invaded even the most remote portions of the Hills. Uncommon animals such as timber rattlesnakes and migratory birds such as the yellow-billed cuckoo, wood thrush and great-crested flycatcher exist in significant numbers in the Tunica Hills while their numbers are decreasing elsewhere.