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. 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 are predominantly silty where loess thickness of the uplands are deepest but grade to loamy textures in watersheds covered by thin loess. Underlying the loess mantle are Tertiary deposits of unconsolidated sand, silt, clay, gravel, and lignite. 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, 2006).
The full distribution of this site is not known as it often occurs as local inclusions within the Northern Wet Loess Terrace site. However, it is highly probable that the site occurs throughout the Loess Plains (EPA Level IV Ecoregion: 74b) from western Kentucky south to the Southern Rolling Plains (EPA Level IV Ecoregion: 74c) in southwestern Mississippi. The reason this site is shown in only two counties is due to the recognition of a ponded phase for an associated soil for this 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: Loess Plains, 74b (Griffith et al., 1998; Woods et al., 2002; Chapman et al., 2004)
-231H - Coastal Plains-Loess section of the USDA Forest Service Ecological Subregion (McNab et al., 2005)
-LANDFIRE Biophysical Setting 4713260 and NatureServe Ecological System CES203.479 South – Central Interior / Upper Coastal Plain Flatwoods (LANDFIRE, 2008; NatureServe, 2009)
-LANDFIRE Biophysical Setting 4713270 and NatureServe Ecological System CES203.479 South – Central Interior / Upper Coastal Plain Wet Flatwoods (LANDFIRE, 2008; NatureServe, 2009)
-Xerohydric Flatwoods – Kentucky State Nature Preserves Commission (Evans et al., 2009)
-Western Mesophytic Forest Region - Mississippi Embayment Section (Braun, 1950)
Ecological site concept
The Northern Ponded Loess Terrace is characterized by deep, poorly drained soils that formed in loess or silty materials. Locations within the Ohio River drainage, the extreme northern extent of the site, were likely formed in clayey lacustrine sediments. This site occurs as depressions on broad, level terraces with ponding typically occurring from winter to mid-spring in most years. These seasonally ponded depressions often occur as inclusions within a much larger ecological site, typically the hydroxeric flatwoods community of the Northern Wet Loess Terrace. Depressional areas differ from the latter in that a much higher proportion of species associated with wetland habitats are generally represented. Species composition appears to be associated with ponding duration. Depressions ponded for longer periods (e.g., winter through late spring or early summer) generally support a greater concentration of wetland obligates such as bald cypress, buttonbush, and arrowleaf. However, ponding duration for most sites is much shorter (3 to 4 months, maximum), with a composition often consisting of pin oak, cherrybark oak, Shumard’s oak, swamp chestnut oak, and overcup oak. Swamp white oak is an additional component in portions of the site’s northern extent.
Northern Wet Loess Terrace - PROVISIONAL
This is the "matrix community" referenced and discussed in this report.
Western Wet Loess Terrace - PROVISIONAL
This site is mapped broadly across the valley train terraces of the Western Lowlands ecoregion and is the western counterpart of the current ecological site.
Southern Rolling Plains Loess Wet Terrace - PROVISIONAL
This site may possibly be the southern counterpart to the Northern Ponded Loess Terrace.
Northern Wet Loess Interfluve - PROVISIONAL
This is the upland counterpart of the current ecological site.
Table 1. Dominant plant species
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