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 primarily occurs on the terraces of the Western Lowlands Pleistocene Valley Trains (EPA Level IV Ecoregion: 73g; Woods et al., 2004), although the soils of the site have been mapped locally on low-lying areas within Crowley’s Ridge and to the east on the Northern Holocene Meander Belts (EPA Ecoregion: 73c; Woods et al., 2004). The distribution of this site spans the boundaries of MLRA 134 and MLRA 131A (Southern Mississippi River Alluvium).
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
-NRCS Major Land Resource Area (MLRA) 131A – Southern Mississippi River Alluvium
-Environmental Protection Agency’s Level IV Ecoregion: Western Lowlands Pleistocene Valley Trains: 73g (Woods et al., 2004); Pleistocene Valley Trains: 73b (Chapman et al., 2002)
-234A – Southern Mississippi Alluvial Plain section of the USDA Forest Service Ecological Subregion (McNab et al., 2005)
-LANDFIRE Biophysical Setting 4515130 and NatureServe Ecological System CES203.193 Lower Mississippi River Flatwoods, respectively (LANDFIRE, 2008; NatureServe, 2009)
-Hardwood Flats, Early Wisconsin Valley Train and Deweyville Terraces (wet phase) (Klimas et al., 2012)
-Bottomland Flatwoods (Nelson, 2005)
Ecological site concept
The Western Wet Loess Terrace is characterized by deep, poorly drained soils that primarily formed in loess or loess-like materials with low sand content. This site occurs primarily on broad, level to nearly level Pleistocene-age terraces with slopes ranging from 0 to 2 percent but dominantly less than 1 percent. Soils have a seasonally high water table from winter to mid-spring that often become quite dry by late summer. This extreme alteration between saturated and droughty conditions is attributed to an impermeable or slowly permeable subsoil layer that is either a fragipan or a dense accumulation of clay. Natural vegetation of these broad flats often resemble or possess characteristics that are suggestive of hydroxeric flatwoods; that is, they have a relatively open understory and support droughty woodland species such as post, southern red, and black oaks. Locally, loblolly pine may become an additional community component farther south. However, considerable variation in the plant community may occur among and between occurrences. Where some local flats are dominated by post oak, others may be dominated by willow oak, and still others may consist of a strange combination of species found in wetlands (e.g., overcup and pin oak) growing beside drought-tolerant trees (e.g., post oak). Embedded within this site are occasional, shallow depressions that pond during the wetter times of the year, generally late winter to spring (typically referred to as vernal pools).
Western Loess Terrace - PROVISIONAL
Western Fragipan Terrace - PROVISIONAL
Western Moderately Wet Terrace - PROVISIONAL
Northern Wet Loess Terrace - PROVISIONAL
Eastern counterpart to the Western Wet Loess Terrace.
Table 1. Dominant plant species
Click on box and path labels to scroll to the respective text.