Floristic affinities of Horse Mountain, Grouse Mountain, Board Camp Mountain, and surrounding areas, Humboldt County, California

Floristic studies are especially timely since habitat loss is increasing dramatically. From the conservation perspective, it is imperative to document the distribution of plant species in areas that are floristically rich. For this study, I conducted a floristic survey along a 20-mile transect in the Horse Mountain, Grouse Mountain and Board Camp Mountain areas of Humboldt County, California. I also determined the phytogeographical affinities of the taxa I found and made comparisons between my flora and 11 other northwest California floras. Additionally, I made a comparison between my flora and the historical collection of Joseph Prince Tracy, a botanist who collected extensively in the same area during the early 1900s. I used an informal stratified sampling regime to cover the different vegetation types within the study area. Five hundred and forty-eight species were identified from 77 vascular plant families, including 18 California Native Plant Society listed taxa and 28 taxa endemic to northwest California. Most had affinities to western North America (273 species) due to the lower elevational position of the study area. One fifth show affinities to the California Floristic Province (124 species, including 23 endemics), and another 17% (96 species, including 5 endemics) had boreal affinities that are found throughout the state's mountains at higher elevations. Some 56 species are not native to the California. I used ordination and cluster analysis to compare my flora to 11 other northwest California floras. These analyses revealed two main groups: (1) montane floras of the Klamath Region and (2) low and montane elevation floras of both the Klamath Mountains (Old Gasquet Toll Road, 58% shared taxa) and Coast Ranges (Lassics and Snow Mountain, both 65% shared taxa). Comparisons between my flora and the Tracy collection found 295 species in common. Of the 439 taxa Tracy documented from the study area and nearby South Fork Mountain, three non-native species were present during his time suggesting an influx of 54 non-native species over the last 60 years.