Conservation of plant and abiotic diversity in grazed and ungrazed meadows of the Sierra Nevada (California).

摘要

Chapter one evaluated our field method using surface moisture classes at the end of August to track species change across the gradient in Kern Plateau meadows, California. As individual species distributions and composition as a whole changed across our a priori moisture classes, and as ordination results showed that moisture class described the majority of variation in species composition, we determined that this method was a good surrogate for the complex hydrologic gradient.; Chapter two examined how impacts on physical characteristics in meadows affect biodiversity. Habitats were characterized by hydrology (moisture class), topography, and gross vegetation physiognomy. Species richness was significantly correlated with habitat richness but not species pool. Diversity on non-channel habitats significantly exceeded that of channel habitats when overhanging banks were removed from the analysis, highlighting the importance of overhanging banks on incised channels. Species richness was higher in dry habitats, but wet habitats had a higher proportion of meadow-dependent species. Stringers were significantly higher in species richness than main meadows.; We concluded that habitat richness was more important than species pool in determining species richness, that non-channelized habitats and stringers contributed most to plant diversity, and that grazing intensity should be controlled in important habitat types: stringers, overhanging banks and willow.; Chapter 3 addressed grazing impacts on channel morphology and incision, moisture class, and species composition by sampling southern Sierra Nevada grazed and ungrazed meadows. Grazed meadows had a significantly higher channel width-to-depth ratio than ungrazed meadows. Channel depth, channel width-to-depth ratio, grazing, and year all significantly affected moisture class distribution. Both greater width-to-depth ratios and grazing were associated with drier moisture classes. Ordination results indicated that grazing, year, and position in basin correlated with the first three axes, explaining 23% of the species data variation. Six ungrazed meadow indicator species, or 43%, were megaforbs, even though megaforbs constitute only 4% of the total flora.; We concluded that cow/calf seasonal grazing is correlated with physical changes in meadow physiography, and that these changes affect moisture class availability and therefore habitat availability. Megaforbs are especially susceptible to impacts of grazing in montane and sub-alpine meadows.