Robin A. Brake and Ruth Ann Kern
Biology Department
California State University, Fresno
Blue oak woodlands are California’s most common hardwood forest, covering nearly three million acres. These woodlands are endangered due to increasing blue oak senescence, as well as environmental stresses related to pollution, suburban expansion, rural building, firewood harvesting, and agricultural/ranching enterprises. Pinus sabiniana is a dominant endemic species of the valley and foothill woodlands surrounding the San Joaquin Valley in California. P. sabiniana, or gray pine, is inexplicably missing in a fifty-five mile segment on the southeastern portion of its potential range. This study hypothesized that P. sabiniana does not grow in the gap due to an environmental gradient established by slope and aspect compared to those areas that do support the species. Field sampling was conducted in foothill woodland research sites situated north, south, and within the range gap at 15 locales in Fresno, Tulare, and Kern counties. Data was collected for 900 point samples during the spring/summer season 2002 and 2003. All tree and shrub species within each point sample were identified and recorded along with the environmental variables of slope, aspect, potential radiation, topographic position, slope configuration, elevation, and the nature and degree of disturbance. Data will be examined using Canonical Correspondence Analysis (CCA) and analysis of covariance to describe the relationship between P. sabiniana distribution and physical site factors. This study is significant in providing much needed research into a historically under-studied community. Because the gray pine is a major associate in the blue oak foothill woodland community, solving the P. sabiniana range discontinuity mystery will add one more piece of information required to sustain the community in a scientifically appropriate manner.