PARENT SESSION
Oral Session #99: Grazing.
Presiding: T. Arredondo
Friday, August 9. 9:00 AM to 12:00 PM. Graham Meeting Room, TCC.
The effects of grazing by Tule elk and cattle on the vegetation dynamics and spider community of coastal salt marshes.
Traut, Bibit*,1, 1 University of California, Davis, Davis, CA
ABSTRACT- Salt marshes in the Point Reyes National Seashore (PRNS) are maintained both as wildland areas and agricultural open space. Yet, the impacts of this multiple use is not well understood, and there is concern that grazing the ecotone between the marsh and upland, the high salt marsh, may negatively impact this threatened habitat. The goal of this study was to determine if excluding cattle and Tule elk would result in increased vegetation complexity (structure and richness) and subsequently affect the spider community. Fenced exclosures were erected in the summer of 1999 at Home Bay (PRNS) and White Gulch (PRNS) to assess impacts of grazing by cattle and Tule elk, respectively. Within each marsh, a 20m x 5m mainplot of the high marsh was selected. Within each mainplot, 10 subplots (2m x 2m) were randomly selected, with 5 randomly established as exclosures and the others 5 left unfenced as controls. After two years, spider diversity and plant biomass, cover and height were measured within the inner 1m x 1m area. Both Tule elk and cattle grazing reduced plant biomass and height and led to increased bareground. Plant richness was not significantly different between cattle grazed and ungrazed plots, but individuals of plant species were more evenly distributed in the exclosures. Whereas in those plots grazed by Tule elk, species richness did increase in exclosures, but without a shift in individual species distributions. I had expected to see a response by the spider community to changes in vegetation structure, but there were no significant differences in spider diversity in any of the grazed or ungrazed plots. These results indicate that trophic generalists in a transition zone, the high salt marsh, may be responding to other factors than vegetation structure alone. Furthermore, grazing in the high salt marsh ecotone shifts plant community structure.
KEY WORDS: salt marsh, grazing, vegetation, spiders