River terraces, Swales, and levees provide limited relief, but overall, it is flatter than neighboring ecoregions in Arkansas, including the South Central Plains.

The ecoregion provides important habitat for fish and wildlife, and includes the largest continuous system of wetlands in North America.

The Mississippi Alluvial Plain has been widely cleared and drained for cultivation; this widespread loss or degradation of forest and wetland habitat has impacted wildlife and reduced bird populations.

Presently, most of the northern and central sections are in cropland and receive heavy treatments of insecticides and herbicides; soybeans, cotton, and rice are the major crops, and aquaculture is also important.

Fish communities in least altered streams typically have an insignificant proportion of sensitive species; sunfishes are dominant followed by minnows.

Small to medium size earthquakes still occur frequently; their shocks are magnified by the alluvial plain's unconsolidated deposits, creating regional land management issues.

Point bars, natural levees, swales, and abandoned channels marked by meander scars and oxbow lakes are common and characteristic.

Overall, soils are not as sandy as the Northern Pleistocene Valley Trains (73b) and are finer and have more organic matter than the Arkansas/Ouachita River Holocene Meander Belts (73h).

Younger sandy soils have fewer oaks and more sugarberry, elm, ash, pecan, cottonwood, and sycamore than Ecoregion 73d.

The Northern Pleistocene Valley Trains ecoregion is a flat to irregular alluvial plain composed of sandy to gravelly glacial outwash overlain by alluvium; sand sheets, widespread in the St. Francis Lowlands (73c), are absent.

They were transported to Arkansas by the Mississippi River and its tributaries and have been subsequently eroded, reduced in size, and fragmented by laterally migrating channels or buried by thick sediments.

Cropland is extensive and has largely replaced the original forests; soybeans, corn, and cotton are the most common crops but wheat, sorghum, and rice are also produced.

The Big Lake National Wildlife Refuge preserves flat flooded swamplands created by the New Madrid earthquakes.

The Northern Backswamps ecoregion is made up of low-lying overflow areas on floodplains, and includes poorly drained flats and swales.

Soils developed from clayey alluvium including overbank and slack-water deposits; they commonly have a high shrink-swell potential and are locally rich in organic material.

In all, about 400,000 acres of prairie grasses and forbs occurred in Ecoregion 73e, and were a sharp contrast to the bottomland forests that once dominated other parts of the Mississippi Alluvial Plain (73).

Rice fields provide habitat and forage for large numbers and many species of waterfowl; duck and goose hunting occurs.

Today, Ecoregion 73f contains some of the most extensive remaining tracts of native bottomland hardwood forest in the Mississippi Alluvial Plain.

Point bars, natural levees, swales, and abandoned channels marked by meander scars and oxbow lakes are common and characteristic.

It flows against the edge of the South Central Plains, receives drainage from it, and has sufficient habitat diversity to be one of the most species-rich streams in North America.

This artificial drainage and the sandy veneer of natural levee deposits help explain why Ecoregion 73i is more easily and widely farmed than the Northern Backswamps (73d).

Macon Ridge (73j) is a continuation of the Western Lowlands Pleistocene Valley Trains (73g) but is better drained, and supports drier plant communities.

[2] The Southern Holocene Meander Belts ecoregion stretches from just north of Natchez, Mississippi south to New Orleans, Louisiana.

Similar to the Northern Holocene Meander Belts (73a), point bars, oxbows, natural levees, and abandoned channels occur.

This region, however, has a longer growing season, warmer annual temperatures, some hyperthermic soils, and more precipitation than its northern counterparts of 73a and 73h.

It is composed of scattered small remnants of early-Wisconsin glacial outwash deposits, similar to those of Macon Ridge (73j).

Some species occur here that are not present in the Macon Ridge (73j) or Western Lowlands Pleistocene Valley Trains (73g) ecoregions to the north in Arkansas.

Bottomland hardwood forests are more prevalent in this region than in the adjacent Southern Holocene Meander Belts (73k), where cropland is common.

Extensive organic deposits lie mainly below sea level in permanently flooded settings resulting in the development of mucky surfaced Histosols.

Lack of sediment input, delta erosion, land subsidence, and rising sea levels threaten the region.