Physiographic features

The Bluff Hills and the Southern Rolling Plains (EPA Level IV Ecoregions 74A and 74C, respectively) of the Southern Mississippi Valley Loess (MLRA 134) are located in southwest Mississippi and southeast Louisiana. The areas lie within the Coastal Plain Province of the Atlantic Plain. The underlying geology consists of marine deposits of sand, silt, clay, and lignite of the Pascagoula, Hattiesburg, Catahoula and Citronelle formations. The Bluff Hills, which bound the Mississippi River floodplain, are capped by loess deposits often greater than 50 feet thick (Chapman et al., 2004). The adjacent terraces of the Southern Rolling Plain are loess mantled as well.

“Loess” is the geologic term of German origin that refers to widespread deposits of homogeneous layers of friable, porous silt mixed with minor amounts of clay or fine sand (Heinrich, 2008). The loess mantle, created by well-sorted windblown silt, was deposited during the Pleistocene age. Its source was glacial sediment from glacial meltwater that was flowing down an extensive braided stream system depositing large volumes of silt over the floodplain of the Mississippi River (Heinrich, 2008). Glacial meltwater ceased flowing when southern edges of ice sheets stopped melting in fall and winter, thereby creating dry conditions on the previously flooded Mississippi River Valley. Strong seasonal winds blew across dry floodplains and eroded large quantities of silt-sized sediment, and transported it out of the Mississippi alluvial valley and deposited it on adjacent uplands and terraces (Heinrich, 2008). Over thousands of years, the silt accumulations created loess deposits that are many feet thick (Heinrich, 2008). The Bluff Hills and Southern Rolling Plains are covered mainly with 2 separate layers (and ages) of loess deposits, the older and lower Sicily Island loess and the younger Peoria loess at the soil surface. In Louisiana, the Sicily Island Hills (composed of basal strata of undifferentiated Catahoula Formation, overlain by Citronelle Formation deposits) are mantled with deep loess (25 to 30 feet thick in places) on the ridgetops and some entire side slopes.

Where blankets of loess are thicker than 6 feet, the soils formed entirely in loess. Where loess deposits are less than 6 feet thick, soils reflect the nature of the underlying parent material (McDaniel, 2001). Thick loess areas produce intensely dissected terrain with excessively steep slopes and ridge and ravine topography (McDaniel, 2001). The Bluff Hills and the Sicily Island Hills tend to have deeper, calcareous loess and steeper, much more dissected topography than the Southern Rolling Plains to the east. The loess mantle on the Southern Rolling Plains begins to thin and become more acid in the east as it transitions to the Southeastern Plains. Stream gradients in the Bluff Hills are high with narrow drainageways and floodplains, while the stream gradients become lower with broader floodplains in the Southern Rolling Plains.

This Site is located in the very steep, highly dissected Sicily Island Hills in Louisiana and the very steep, highly dissected Bluff Hills adjacent to the Mississippi River floodplains and the very western portion of the uplands of the Southern Rolling Plains in Mississippi and Louisiana. In extreme southwest Mississippi and adjacent area in Louisiana, the site is in an area locally known as the Tunica Hills. This site occurs on long, narrow, winding ridgetops and steep and very steep side slopes, upper parts of drainageways, and sharp breaks near ridgetops. Slopes mainly range from steep to very steep (12 to 90 percent), and erosion is a severe hazard. Many of these sites are in eroded to severely eroded areas with gullies cutting through unstable sideslopes and drainageways.

Table 2. Representative physiographic features

Climatic features

The Southern Bluff Hills portions of MLRA 134 in Mississippi and Louisiana has a warm, humid climate, with fairly long summers and relatively short winters. The result is a long growing season and abundant plant growth. As you move northward in this region temperature trends lower and Precipitation is not as well distributed. This change in distribution does not imply that there is a rainy season and dry season, however there is a change in distribution. Water is a definitive part of this landscape, largely due to the combination of low elevation and fairly abundant rainfall in most years. Mean annual precipitation ranges from 50 to 70 inches over this region, and is fairly well distributed throughout the year. There have been very few years when less than 50 inches of precipitation has fallen. Snow is a rarity, however chances increase as you move Northward through the region. Growing seasons are long, typically from late February to late November. Hurricanes and tropical storms impact the climate of this region predominately in the southern areas, with some impact occurring nearly every year in some areas. However, devastating storms do not occur too often, and heavy rain is usually the biggest concern compared to wind damage. The following climatic data are averages from the four weather stations listed below. Temperature and precipitation may vary considerably from that listed for each month. Site specific weather data should be used for land management decisions. For site specific weather conditions, obtain data from a weather station close to the site. Information can be accessed from specific weather stations at http://www.wrcc.dri.edu/coopmap/ or http://www.wrcc.dri.edu/summary/climsmla.html.

Table 3. Representative climatic features

Climate stations used

• (1) NATCHEZ [USC00226177], Natchez, MS

• (2) PORT GIBSON 1 NE [USC00227132], Port Gibson, MS

• (3) WOODVILLE 4 ESE [USC00229793], Centreville, MS

• (4) BATON ROUGE RYAN AP [USW00013970], Baton Rouge, LA

Influencing water features

This site is influenced mostly by surface hydrology. The Slope greater than 12% will shed rainfall and reduces the amount that will be available for plant growth. However as you near the footslopes at the lower end of this site available water may increase as sub-surface moist flows laterally within the profile.

Soil features

Soils are well drained Typic Hapludalfs (Memphis), Ultic Hapludalfs (Feliciana), Typic Eutrudepts (Natchez), and somewhat excessively drained Typic Udorthents (Fortadams). These steep to very steep soils formed in thick loess deposits in the highly dissected Bluff Hills, the Sicily Island Hills, and the western portion of the Southern Rolling Plains in the Southern Mississippi Valley Loess (MLRA 134). Slopes range from 12 to 90 percent. These deep, moderately permeable soils are found on mainly on narrow, winding ridgetops and steep to very steep, unstable side slopes. These soils have relatively few restrictions for plant growth. These soils have medium fertility, but could possibly have moderately high to high levels of exchangeable aluminum that are potentially toxic to plants. The seasonal high water table is at a depth of more than 6 feet below the surface. Erosion hazard is severe and limits land use potential. Many of these soils are in eroded to severely eroded areas with gullies cutting through unstable sideslopes and drainageways.

The soils listed in this section of the description may not be all inclusive. There may be other soils that fit this site concept, as well as in some areas where the listed soils are mapped they may not fit the site concept. Some soil map units and soil series included in this Provisional Ecological Site grouping were used as “best fit” for a particular soil-landscape catena during a specific era of soil mapping, regardless of origin of parent material or Major Land Resource Area. Therefore, these soil series may not be typical for MLRA 134, and those soil map units deserve further investigation in a joint ecological-soil survey project. When utilizing this description verify it is the correct site utilizing multiple parameters, the soils, the physiography and the location. If the site does not fit the particular location well utilize the Similar or Associated Sites listed in the Supporting Information section of this description to determine if another site may be a better fit to your location.

Table 4. Representative soil features

Other references

Autin, W. J., Burns, S. F., Miller, B. J., Saucier, R. T., & Snead, J. I. (1991). Quaternary geology of the lower Mississippi Valley. The Geology of North America, 2, 547-582.

Chapman, S.S, Griffith, G.E., Omernik, J.M., Comstock, J.A., Beiser, M.C., and Johnson, D., 2004, Ecoregions of Mississippi, (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey (map scale 1:1,000,000).

Cowardin, L. M., Carter, V., Golet, F. C., & LaRoe, E. T. (1979). Classification of wetlands and deepwater habitats of the United States. US Fish and Wildlife Service FWS/OBS, 79(31), 131.

Daigle, J.J., Griffith, G.E., Omernik, J.M., Faulkner, P.L., McCulloh, R.P., Handley, L.R., Smith, L.M., and Chapman, S.S., 2006, Ecoregions of Louisiana (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey (map scale 1:1,000,000).

Emerson, F. V. (1918). Loess-depositing winds in Louisiana. The Journal of Geology, 26(6), 532-541.

Ezell, A. W., & Hodges, J. D. (1995). Bottomland hardwood management: Species Site Relationships. MSU Extension Service Publication 2004.

Guyette, R. P., Stambaugh, M. C., Dey, D. C., & Muzika, R. M. (2012). Predicting fire frequency with chemistry and climate. Ecosystems, 15(2), 322-335.

Heinrich, P. V., (2008)_Loess Map of LA, Louisiana Geological Survey

Kochian, L. V., Pineros, M. A., & Hoekenga, O. A. (2005). The physiology, genetics and molecular biology of plant aluminum resistance and toxicity. In Root Physiology: From Gene to Function (pp. 175-195). Springer Netherlands.

Miller, B. J., Lewis, G. C., Alford, J. J. & Day, W. J. (1984) Loesses in Louisiana and at Vicksburg, Mississippi. Guidebook for Friends of the Pleistocene Field Trip.

Miller, B. J., Day, W. J., & Schumacher, B. A. (1986). Loesses and loess-derived soils in the Lower Mississippi Valley. Guidebook for soils-geomorphology tour.

Pettry, D. E., & Switzer, R. E. (1998). Sodium soils in Mississippi.

Rutledge, E.M., M.J. Guccione, H.W. Markewich, D.A. Wysocki, and L.B. Ward. 1996. Loess stratigraphy of the Lower Mississippi Valley. Engineering Geology 45: 167-183.

Saucier, Roger T. 1994. Geomorphology and Quaternary Geologic History of the Lower Mississippi Valley, Volume I & II. U.S. Army Corps of Engineers, Vicksburg, MS.

Schumacher, B. A., Miller, B. J., & Day, W. J. (1987). A chronotoposequence of soils developed in loess in central Louisiana. Soil Science Society of America Journal, 51(4), 1005-1010.

Theriot, R. F. (1992). Flood tolerance of plant species in bottomland forests of the southeastern United States.

United States Salinity Laboratory Staff, USA, USDA (1954), Diagnosis and improvement of saline and alkali soils, USDA Agriculture Handbook 60,1954, 160 pp.

Contributors

D Charles Stemmans II
Rachel Stout Evans