Landscape and local variation in mixed evergreen forest composition related to Phytophthora ramorum (Sudden Oak Death) near Big Sur, California

Background/Question/Methods Mixed evergreen forests of central coastal California have been dramatically impacted by the recently introduced plant pathogen, Phytophthora ramorum. Surprisingly little is known about composition or dynamics of these forests, even in the absence of P. ramorum, making it difficult to evaluate longer term impacts of the disease in the region. We collected forest plot data using a multi-scale sampling design to characterize forest composition, disease incidence and tree mortality along environmental and time-since-fire gradients.

Results/Conclusions Species local abundance is strongly correlated with regional frequency. Forest composition shifts locally along topo-moisture gradients and regionally along gradients from moist coastal sites to drier interior sites. Most dominant tree species sprout vigorously after burning and there is only weak relationship between forest composition and time since burning.  Lithocarpus densiflorum is the most frequent tree species in our sample and also the most impacted by P. ramorum. L. densiflorum mortality is higher on northeast facing slopes. Contrary to expectations, mortality is not significantly associated with basal of Umbellularia californica, an important host for the disease, probably because the disease has not yet spread across the entire study region.