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ABSTRACT. Zebra mussels, Dreissena polymorpha, were collected monthly from April/May to November in 1990 and

Summary0 Submergence of coastal wetlands in Louisiana is currently rapid and widespread[ A number of factors contribute to this loss of habitat\ including the activities of herbivores[ The objective of this study was to examine the e}ects of large mammals\ predominantly nutria and wild boar\ on processes controlling soil elevation in coastal marshes[

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Both vertebrate herbivores and fire have long been known to have dramatic and important effects on wetland vegetation. However, the interactive effects of burning and herbivory have received less attention. In this study, conducted in the coastal marshes of the Pearl River Basin in Louisiana, USA, both the effects of herbivory and fire as well as the interaction between these effects were examined in three marsh community types: Sagittaria lancifolia, Panicum virgatum, and Spartina patens. At five sites for each of the three cc~mmunity types, the effects of burning and fencing to exclude herbivores were determined over two years.Results showed that total biomass was reduced by burning but increased by fencing, with no interactive effects on total biomass. Species density (the number of species per unit area) was enhanced in plots that were both burned and fenced. Spartina patens was an important component in all three communities. Cover estimates indicated that S. patens responded to burning and fencing differently from the other dominant species. In the Panicum virgatum community, P. virgatum cover was enhanced by burning and fencing while S. patens cover was reduced. In the Sagittaria lancifolia community, S. lancifolia and Vigna luteola were enhanced by burning and fencing while S. patens was reduced. In the S. patens community, Scirpus americanus was enhanced by fencing, but burning had no significant effect on cover of either dominant species. These and other data are generally consistent with the hypothesis that herbivory favors S. patens while burning favors other dominant species. Thus, the relative effects of fire and herbivory have an influence (along with other factors such as salinity) on the dominance of S. patens in coastal marshes.

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