Physiographic features

The Baton Rouge Terrace (EPA Level IV Ecoregions 74D) of the Southern Mississippi Valley Loess (MLRA 134) are located in southeast Louisiana, occurs on the Pleistocene Prairie Terraces and is lower in elevation and has flatter topography than Ecoregion 74c to the north. Similar to other parts of Ecoregion 74, loess is thicker to the west.

“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).

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 tend to have deeper, calcareous loess and steeper, much more dissected topography than the Southern Rolling Plains to the east and Baton Rouge Terrace to the Southeast.

This Site occurs mainly on the broad floodplains of creeks and streams and their tributaries draining the Southern Rolling Plains in Louisiana. Smaller areas of this site occur on the narrow drainways and floodplains of the smaller creeks and streams within the Bluff Hills of Louisiana. This site also occurs as "Gallery Forests" in the "Cajun Prairie" Region of MLRA 134, Ecoregion 34j the Lafayette Loess plain. Slopes are level to nearly level (0 to 3 percent).

Table 2. Representative physiographic features

Climatic features

South 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. Water is a definitive part of the southern Louisiana landscape, largely due to the combination of low elevation and fairly abundant rainfall in most years. Mean annual precipitation ranges from 51 to 67 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, and little more than 1 inch typically falls every few years. Growing seasons are long, typically from late February to late November. Along the gulf coast, it is not unusual for the lowest winter temperature to be above 30 degrees. Inland, there have been occasional blasts of cold air that have dropped temperatures into the teens and 20s, but these are rare. Hurricanes and tropical storms are an important part of the climate of southern Louisiana, with some impact occurring nearly every year in some part of the region. However, devastating storms do not occur too often, and heavy rain and storm surge are usually the biggest concerns, compared to wind damage. The following climatic data are averages from the five 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) CLINTON 5 SE [USC00161899], Clinton, LA

• (2) LAFAYETTE [USC00165021], Lafayette, LA

• (3) NEW IBERIA ACADIANA AP [USC00166657], New Iberia, LA

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

• (5) LAFAYETTE RGNL AP [USW00013976], Breaux Bridge, LA

• (6) LSU BEN-HUR FARM [USC00165620], Baton Rouge, LA

• (7) GRAND COTEAU [USC00163800], Opelousas, LA