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Northern Holocene Meander Belts

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About the Northern Holocene Meander Belts

The Northern Holocene Meander Belts are a section of the Mississippi Alluvial Plain extending from the extreme southern tip of Illinois, through Kentucky and Missouri, Tennessee, and Arkansas, into Mississippi and northern Louisiana. It covers much of the eastern portions of the Mississippi Alluvial Plain but does not extend into its southernmost portions. This previously highly biodiverse area has been aggressively utilized for agriculture through clearing of most of the bottomland forests and extensive drainage and channelization.

This region consists of broad, nearly level floodplains, low terraces, islands, and abandoned channels of the Mississippi river and its tributaries, with numerous features characteristic of a broad floodplain of a major river, including oxbow lakes, shallow ponds, back swamps, natural levies, sloughs, and point bars. Streams are uncommon and tend to be winding and low-gradient. Soils are all formed on relatively recent alluvial deposits, and tend to be high in nutrients, varying in texture from moderately well-drained to very poorly-drained, with the best-drained soils tending to occur closest to the rivers or more recently-abandonded channels. The water table is consistently high, and many areas flood seasonally.

The climate is humid and subtropical, with significant variation in winter lows over the length of this region; although the north is colder, the low elevations and abundance of water tends to make this region have some of the mildest winter temperatures of any areas extending so far north and inland.

At the time of European settlement, this region was mostly covered in bottomland forests, with bottomland swamps on the most frequently-flooded sites. Many southern species reach their northern range limits here. Better-drained areas, including natural levees, supported bottomland forest of American sweetgum (Liquidambar styraciflua), sugarberry (Celtis laevigata), red maple (Acer rubrum), slippery elm (Ulmus rubra), pecan (Carya illinoinensis), overcup oak (Quercus lyrata), willow oak (Quercus phellos), eastern cottonwood (Populus deltoides), American sycamore (Platanus occidentalis), and water hickory (Carya aquatica), and in the north of this region, pin oak (Quercus palustris), and in all but the northernmost portions, water oak (Quercus nigra), cherrybark oak (Quercus pagoda), and swamp chestnut oak (Quercus michauxii), and in the far south, nuttall's oak (Quercus texana). Swamps supported bald cypress (Taxodium distichum) and water tupelo (Nyssa aquatica). Sandbars were often dominated by pure stands of black willow (Salix nigra). Point bars supported diverse forests with black willow on the newest-deposited soil, followed by river birch (Betula nigra), then developing into more diverse assemblages of eastern cottonwood, sugarberry, sycamore, green ash (Fraxinus pennsylvanica), and pecan. The south of this region in Mississippi and Louisiana also had some forested canebreaks with scattered deciduous trees amongst giant cane (Arundinaria gigantea).

This area has been heavily altered through channelization and drainage of wetlands. Forests have been mostly cleared, with only scattered fragments of forest found on the most poorly-drained sites. An overwhelming majority of this area is now used for cropland, producing livestock, soybean, corn, wheat, sorghum, hay, and in all but the north, rice, and cotton. There is also some commercial catfish production and pastureland in the south. Channelization projects may have increased the prevalence of river birch here, which readily colonizes soils exposed in these projects.

In spite of the alterations humans have made to this region, greatly reducing wetland habitat, it still has immense value to water birds. There has been some restoration of the bottomland forests since around 1985.

Most of this region is sparsely populated, but there is some urbanization; it contains the small cities of Cairo, IL, West Memphis, AR, Blytheville, AR, and part of Greenville, MS, as well as numerous smaller towns. As this region is flood-prone, all of these cities have suffered damaging and often dangerous floods. This region has a majority-black population originating as slaves to plantations in this region, and tends to be significantly poorer than nearby regions on safer, drier ground.

This region is interspersed with other regions of the Mississippi Alluvial Plain, including the Northern Backswamps and the Northern Pleistocene Valley Trains. It is bordered to the south by the Southern Holocene Meander Belts, a geologically-similar region separated due to differences in climate and vegetation; the cutoff between these two areas is arbitrary and represents a gradual transition. This region is bordered to the west by the St. Francis Lowlands in the north, the Western Lowlands Pleistocene Valley Trains south of that, and then the Arkansas/Ouachita River Backswamps in some areas, and the Macon Ridge in others. To the east, it is bordered by the Mississippi Valley Loess Plains, by the Bluff Hills where steep bluffs are found, and by the Loess Plains in the flatter areas.

References

1. Woods, A.J., Omernik, J.M., Martin, W.H., Pond, G.J., Andrews, W.M., Call, S.M, Comstock, J.A., and Taylor, D.D. "Ecoregions of Kentucky (Poster)", U.S. Geological Survey, Reston, VA (2002) Web.

2. Griffith, G.E.; Omernik, J.M.; and Azevedo, S.H. "Ecoregions of Tennessee (Poster)", U.S. Geological Survey, Reston, VA (1998) Web.