| Abstract: | Transformation of emergent coastal marsh to mudflats has been noted on the San Bernard National Wildlife Refuge, Texas in areas utilized by wintering lesser snow geese (LSG). Interaction of LSG herbivory and environmental dynamics was investigated at several spatial and temporal scales to determine the extent of mudflat development and the potential for vegetation reestablishment. Historical mudflat/vegetation dynamics from 1939 to 1991 were evaluated from aerial photography utilizing a geographic information system. Less than 4% of the areas was unvegetated in 1939 while 21% was unvegetated in 1991. Rate of mudflat development increased after 1965 following heavy LSG use. Some mudflats revegetated, while others became deeper, open water areas. Distichlis spicata/Spartina alterniflora dominated areas denuded by LSG contain remnant vegetation islands (2-4 m^2). Both heavy- and light-use areas of D. spicata islands had reduced foliar cover and height for the 2.5 years of the study. Islands expanded without further LSG use. Rate of expansion was initially delayed by summer drought and algal mat accumulation. Expansion rate accelerated with increased hydroperiod, reduced salinities and decreased algal mat. Regardless of herbivory level, increased salinity and reduced hydroperiod resulted in low cover values of D. spicata and high Salicornia virginica values. Conversely, reduced salinity and increased hydroperiod resulted in increased D. spicata with a concomitant decrease in S. virginica. The interaction of LSG herbivory, prescribed burning and environmental dynamics was investigated in Scirpus Olneyi communities. LSG utilization of S. Olneyi rhizomes and roots initially reduced cover. Burning did not significantly affect the response variables of S. Olneyi. Regrowth mechanism was reestablishment of uprooted crown material. Spring water levels below the marsh surface and high interstitial soil salinities resulted in a lack of uprooted S. Olneyi regeneration. Lowest regrowth occurred in areas used most intensely followed by spring drought, while highest regrowth was associated with low intensity use followed by spring freshwater inflows. Continued frequent and intense use of the marsh vegetation, coupled with low water and high salinity, can produce slow to revegetate mudflats. Areas more frequently influenced by tide have the potential for accelerated soil erosion. |
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