VEGETATION AND FLORA OF A BIODIVERSITY HOTSPOT: PINE HILL, EL DORADO COUNTY, CALIFORNIA, USA

摘要

Pine Hill lies near the center of a gabbrodiorite intrusion in the foothills of the Sierra Nevada mountain range in El Dorado County, CA, USA. We assembled an extensive flora, examined the distribution and associations of vascular plant taxa, and specifically focused on associations of six rare plant taxa. The influence of environmental variables on plant distribution was investigated using a stratified random plot sampling technique and applying canonical correspondence analyses. The site contained over 10% (741 plants) of the flora of the entire state of California including seven rare species. Species segregated into chaparral, oak woodland, and grassland communities. In chaparral and woodland, and on serpentine sites, over 75% of the flora was comprised of native species. The non-serpentine grassland community was dominated by exotic species (64% exotic) and contained no rare species. Shrub and tree cover were the most important biotic factors associated with plant species distribution; serpentine substrate, soil texture, elevation, and degree of disturbance were the most important abiotic factors. Five rare species were restricted to gabbro soils. Consideration of beta diversity contributed little to our understanding of vegetation patterns. Our analyses identified two types of chaparral which we termed "Xeric Seeding" and "Mesic Resprouting" to reflect the environmental conditions and the fire regeneration strategy of the vegetation. Each chaparral type contained different rare species whose regeneration strategies were concordant with chaparral regeneration type.