Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.
Major Land Resource Area (MLRA): 134X–Southern Mississippi Valley Loess
The Southern Mississippi Valley Loess (MLRA 134) extends some 500 miles from the southern tip of Illinois to southern Louisiana. This MLRA occurs in Mississippi (39 percent), Tennessee (23 percent), Louisiana (15 percent), Arkansas (11 percent), Kentucky (9 percent), Missouri (2 percent), and Illinois (1 percent). It makes up about 26,520 square miles. Landscapes consist of highly dissected uplands, level to undulating plains, and broad terraces that are covered with a mantle of loess. Underlying the loess are Tertiary deposits of unconsolidated sand, silt, clay, gravel, and lignite. The soils, mainly Alfisols, formed in the loess mantle. Stream systems of the MLRA typically originate as low-gradient drainageways in the upper reaches that broaden rapidly downstream to wide, level floodplains with highly meandering channels. Alluvial soils, mostly Entisols and Inceptisols, are predominantly silty where loess thickness of the uplands are deepest but grade to loamy textures in watersheds covered by thin loess. Crowley’s Ridge, Macon Ridge, and Lafayette Loess Plains are discontinuous, erosional remnants that run north to south in southeastern Missouri - eastern Arkansas, northeastern Louisiana, and south-central Louisiana, respectively. Elevations range from around 100 feet on terraces in southern Louisiana to over 600 feet on uplands in western Kentucky. The steep, dissected uplands are mainly in hardwood forests while less sloping areas are used for crop, pasture, and forage production (USDA-NRCS, 2006).
This site occurs on floodplains of small drainageways to large streams that mainly drain upland areas of Crowley’s Ridge from about Forrest City, Arkansas northward through Stoddard County, Missouri.
All or portions of the geographic range of this site falls within a number of ecological/land classifications including:
-NRCS Major Land Resource Area (MLRA) 134 – Southern Mississippi Valley Loess (USDA-NRCS, 2006)
-Environmental Protection Agency’s Level IV Ecoregion: Bluff Hills, 74a (Chapman et al., 2002; Woods et al., 2004)
-231H - Coastal Plains-Loess section of the USDA Forest Service Ecological Subregion (McNab et al., 2005)
-LANDFIRE Biophysical Setting 4514730 Gulf and Atlantic Coastal Plain Floodplain Systems (LANDFIRE, 2008)
- East Gulf Coastal Plain Small Stream and River Floodplain Forest CES203.559 (NatureServe, 2012)
-Mesic Bottomland Forest (Nelson, 2005)
-Western Mesophytic Forest Region - Mississippi Embayment Section - Loess Hills (Braun, 1950)
Ecological site concept
The Western Alluvial Flat is characterized by deep, well drained to moderately well drained soils that formed in silty to loamy alluvium. Soil reactions range from very strongly acid to strongly acid in all horizons. This site occurs primarily on better drained portions (higher positions) of narrow to broad floodplains and secondarily on alluvial fans. Within stream and floodplain environments, specific landforms associated with the site include natural levees, rises, and the better drained flats that often border the stream-front or levee position. Flooding ranges from rare to frequent during winter and spring, and duration is brief to very long depending on stream and drainage basin size and flood event. Slopes are variable and dependent on floodplain position; dominant slopes of the flats are 0 to 2 percent but range to 5 percent on natural levees. The native vegetation of this site is the fabled, southern bottomland hardwood forest. The better drainage capabilities of the soil provide an incredible medium for supporting exemplary examples of upland and lowland species co-occurring within single stands. Overstory components often include cherrybark oak, white oak, willow oak, water oak, Shumard’s oak, swamp chestnut oak, tuliptree, American beech, American sycamore, sweetgum, maple, eastern cottonwood, hickories, elm, river birch, and green ash.
Western Moderately Wet Alluvial Flat - PROVISIONAL
This site occurs in close association with the Western Alluvial Flat and is characterized primarily by somewhat poorly drained soils.
Southern Rolling Plains Loess Stream Terrace - PROVISIONAL
This site occurs in the southeastern extent of MLRA 134 and supports similar soils and landform characteristics as the Western Alluvial Flat.
Northern Alluvial Flat - PROVISIONAL
This site is the eastern counterpart to the Western Alluvial Flat and includes similar soils.
Table 1. Dominant plant species
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