Masters Thesis

Conservation of globally and locally rare plant taxa in Napa County, California

Napa County is located within a global biodiversity hotspot, and is one of ten localized areas in California that contain the highest numbers of native and endemic plant species. Conservation of rare taxa is an important issue and the research presented here focuses on the globally, sub-nationally, and locally rare plants of Napa County. Initially, a checklist of the flora of Napa County is developed by combining and reviewing local and statewide data sources. Next, a local rarity classification system is developed and tested. Using a geographic information system, the distributions and hotspots of globally, sub-nationally, and locally rare plants in Napa County are identified. Finally, correlation between rarity, habitat types, and protected lands are assessed. The final native plant checklist for Napa County includes 1418 taxa. At global and sub-national assessment scales, 126 native taxa in Napa County are listed as rare or threatened by the California Natural Diversity Database element ranking system. Aditionally, 89 taxa meet the area of occupancy criteria for rarity status at the local assessment scale. Analysis of the distributions of all rare plant taxa indicates that there are several rarity hotspots in Napa County that only somewhat correspond among different assessment scales as well as with specific habitats and current protected lands. Results from this study make it apparent that Napa County contains remarkably high levels of plant diversity and intense concentrations of special status taxa in several locations. Multiple conservation strategies are necessary to protect the flora of this unique area.

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