Effects of Sudden Oak Death on Coast Live Oak Woodland Vegetation Structure
Letty Brown1 and Barbara Allen-Diaz2
This study seeks to identify correlates between the spread of non-native Phytophthora ramorum and the structure of native coast live oak (Quercus agrifolia) plant communities. We compare stand structure, plant species composition, and environmental characteristics in coast live oak woodlands over a gradient of Sudden Oak Death (SOD) infection. The primary objective is to establish baseline information about the types and rates of change in successional pathways, including the potential for species invasions and effects on vegetation productivity. Five 1-ha plots have been established; 3 in Marin County and 2 in Contra Costa County. Within each 1-ha plot, five 0.08 ha subplots were established to sample species composition of herbaceous, shrub, and tree layers, tree seedling density, tree diameter and height, and SOD disease characteristics. Tissue samples from all plots are being collected and tested for presence of P. ramorum. Environmental attributes include slope, aspect, elevation, light intensity, and soil type. Characteristics of downed woody debris are also recorded. On the 25 sub-plots established thus far, slope varies between 20% and 60%, with a 40% average. All aspects are represented, but plots tend to occur in mesic Q. agrifolia community types with California bay (Umbellaria californica), black oak (Quercus kelloggii), and/or buckeye (Aesculus californica), or madrone (Arbutus menziesii) represented. As an indicator of slightly drier sites, toyon (Heteromeles arbutifolia) may be present but with much less frequency than the other tree species. Understory herbaceous and shrub species in these stands tend to be sparse. In order to establish additional uninfected control plots, we will incorporate plots in Mendocino and San Luis Obispo counties. This research is funded by the USDA Pacific Southwest Station of the Forest Service and is part of a larger study that includes research by collaborators in tanoak (Lithocarpus densiflorus) communities, and estimates of reptiles and amphibians, small mammals, and birds utilizing these SOD-infected and uninfected sites.
1Dept. of Environmental Science, Policy and Management- Ecosystem Sciences, 151 Hilgard Hall, University of California, Berkeley, CA 94720-3110; lbrown@nature.berkeley.edu
2Dept. of Environmental Science, Policy and Management- Ecosystem Sciences, 151 Hilgard Hall, University of California, Berkeley, CA 94720-3110; ballen@nature.berkeley.edu
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