Species diversity increases on levees and ridges as a larger variety pf 

 plants are capable of tolerating the more favorable growth conditions (Spindler 

 and Noble, 1974). Plant biomass levels may meet or exceed production levels 

 in adjacent marsh systems (Willingham et al., 1975). Dead plant biomass enters 

 the detrital storage and may contribute to soil enrichment through the microbe- 

 nutrient complex, or it may be exported to adjacent systems through surface 

 runoff (Buckman and Brady, 1969; Willingham et al., 1975; Darnell, 1976). Plant 

 biomass increases the infiltration rate of surface water into the soil macropore 

 water, reduces the rate of surface water runoff, and thereby diminishes the 

 associated erosion processes. This particular aspect is important in stabilizing 

 new levee and spoil areas (Darnell, 1976). 



Plant succession on spoil banks and levees is regulated by two agents, 

 fire and subsidence. As in other systems, fire retards succession or returns 

 it to earlier seres. On coastal marsh levees, woody growth, typically groundsel, 

 will be replaced by marshhay cordgrass or other grassy species following repeated 

 burning. Pioneering species are encouraged and species diversity is increased 

 (Spindler and Noble, 1974), Subsidence of the levee system will cause a return 

 to the marsh vegetation that existed before land elevation occurred (Bourn and 

 Cottam, 1950; Spindler and Noble, 1974). 



Terrestrial and semiaquatic consumer groups derive various inputs from 



tne increased habitat diversity associated with elevated sites. The type and 



amount of inputs received depends upon the cover types present, the system's 

 extent, its location, and the local faunal species. 



Elevated levees and ridges serve as travel lanes for terrestrial organisms 

 feeding in the wetlands but residing in nearby uplands - for example, white- 

 tailed deer, raccoon, coyote and livestock (Lay and O'Neil, 1942). In addition, 

 marsh levees and spoil areas may function as habitat extensions for species 

 typically associated with more upland environs: for example, swamp rabbit 

 ( Sylvilaqus aquaticus ), eastern cottontail ( Sylvilagus floridanus ), hispid cotton 

 rat, bobwhite, and numerous other granivorous songbirds. The stratified and 

 often dense vegetation can fulfill particular nesting, refuge, and resting cover 

 requirements for numerous wetland species. Nutria, muskrat, mink ( Mustela 

 vison ), otter ( Lutra canadensis ), alligator, and numerous snakes routinely use 

 high points in the marsh as sunning or resting locations (Lay and O'Neil, 1942). 

 Herons and egrets may nest or roost in the woody growth atop levees. Many 

 species of nesting birds are attracted by the diversity of plant strata, plant 

 composition, and abundant insect populations. Cheniers and levees provide refuge 

 areas during periods of high water in the marsh (Lay and O'Neil, 1942). 



NATIONAL WILDLIFE REFUGE DESCRIPTIONS 



This section contains a description of the location, geology, soils and 

 topography, climatology, hydrology, vegetation, and wildlife of each of the 

 refuges studied. Figure 3-10 shows the ecosystems present in each of the 

 refuges. 



55 



