Locally rare plant taxa in Napa County, CA: Testing the efficacy of L-rank criteria

Background/Question/Methods

The ecological and evolutionary significance of locally rare plant taxa has been well discussed in the literature. Yet, these taxa have not been well integrated into conservation planning largely due to a lack of distribution data and a system for summarizing their status.  To address this concern, we have developed a set of criteria called L-ranks for categorizing locally rare taxa that largely conform to the G- and S-ranks developed by the Natural Heritage Network (NatureServe). Furthermore, we incorporate aspects of the Red List Criteria developed by the International Union for the Conservation of Nature. In this study, we test the utility of these criteria using the flora of Napa County. We conducted GIS analyses of distributions using 1km x 1 km grids.

Results/Conclusions

Our preliminary analyses indicate that among the 1418 native plant taxa in the county, 56 are considered locally rare based on our criteria.   Furthermore, over 4% of the area of Napa County contains 20 or more locally rare plant taxa.  These hotspots of locally rare plants correspond to some extent with global rare plant hotspots.