Gap Analysis of the Actual Vegetation
of California: The Southwestern Region
Frank W. Davis, Peter
A. Stine, David M. Stoms, Mark I. Borchert, and Allan D. Hollander
Gap Analysis is a method of conservation
risk assessment that evaluates the protection status of plant communities,
animal species and vertebrate species richness by overlay of biological
distribution data on a map of existing biological reserves. The National
Biological Survey has undertaken a national Gap Analysis that is being
conducted by individual states but that will eventually produce regional
and national assessments. Given California's size and complexity,
we are conducting separate Gap Analyses for each of the state's 10
ecological regions, as delineated in The Jepson Manual. Here we summarize
our findings on the distribution of plant communities and dominant
plant species in the Southwestern Region of California, exclusive
of the Channel Islands. We tabulate and discuss regional distribution
patterns, management status and patterns of land ownership for 76
dominant woody species and 62 natural communities. Nineteen of 62
mapped communities appear to be at risk, as determined by their poor
representation in existing reserves, parks or wilderness areas. Communities
restricted largely to the lower elevations, such as non-native grasslands
and coastal sage scrub types, are clearly at considerable risk. A
majority of the lands at these elevations have already been converted
to agricultural or urban uses and most of the remaining lands are
threatened with future urbanization. Areas that appear to be of highest
priority for conservation action based on agreement between our analysis
and a recent assessment by The Nature Conservancy include the Santa
Margarita River, San Mateo Creek, Miramar Mesa, Santa Clara floodplain
near Fillmore, Sespe and Piru Canyons, and Tejon Pass.