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.
Figure 1. Mapped extent
Areas shown in blue indicate the maximum mapped extent of this ecological site. Other ecological sites likely occur within the highlighted areas. It is also possible for this ecological site to occur outside of highlighted areas if detailed soil survey has not been completed or recently updated.
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 is restricted to the uplands of Crowley’s Ridge from Helena, Arkansas north through Stoddard County, Missouri. [Note that the distribution of this site as shown extending west of Crowley’s Ridge (the Loess Hills in pink) onto the Western Lowland terraces (yellow) is an artifact of soil mapping and does not reflect the actual distribution of this ecological site.]
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
-Environmental Protection Agency’s Level IV Ecoregion: Bluff Hills, 74a (Griffith et al., 1998; Woods et al., 2002; Chapman et al., 2002; Chapman et al., 2004; Woods et al., 2004; Daigle et al., 2006)
-231H - Coastal Plains-Loess section of the USDA Forest Service Ecological Subregion (McNab et al., 2005)
-NatureServe Ecological System CES203.071: Mississippi River Alluvial Plain Dry-Mesic Loess Slope Forest (NatureServe 2011)
-Mixed Oak – Hickory Forest Type (Clark et al., 1974)
-Dry-Mesic Loess Forest; Dry-Mesic Loess Woodland (Nelson, 2005)
-Western Mesophytic Forest Region - Mississippi Embayment Section - Loess Hills (Braun, 1950)
Ecological site concept
The Western Fragipan Upland is characterized by deep, moderately well drained soils that formed in a mantle of loess. Soils often perch water during wet seasons and/or high rainfall events due to moderately slow to slow permeability in a dense subsoil layer, typically a fragipan. This site occurs on narrow to broad, upland interfluves to strongly sloping sideslopes. Slopes range from 0 to 20 percent, but dominant gradients are 2 to 12 percent. The natural vegetation prior to settlement likely consisted of a dry-mesic oak – hickory association throughout much of Crowley’s Ridge. However, local inclusions of drier vegetation components such as shortleaf pine and black hickory likely occurred in areas where the soils of this site are in close proximity to and in association with thin loess soils and exposed fluviomarine deposits (gravel and sand). Fire may have been an important influence on both community structure and composition in the northern portions of Crowley’s Ridge but potentially less so toward the southern end.
Northern Deep Loess Backslope Mesophytic Forest
This site joins the Western Fragipan Upland in portions of the southern and northern end of Crowley's Ridge.
Northern Deep Loess Summit - PROVISIONAL
This site joins the Western Fragipan Upland where thick loess soils (no fragipan) occur.
Western Dry Loess Backslope - PROVISIONAL
Western Dry Loess Summit - PROVISIONAL
Southern Rolling Plains Loess Fragipan Upland - PROVISIONAL
This site is the southeastern counterpart to the Western Fragipan Upland.
Northern Loess Fragipan Upland - PROVISIONAL
This site is the northeastern counterpart to the Western Fragipan Upland.
Table 1. Dominant plant species
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