Impacts of Sudden Oak Death on forests of the Big Sur Region of California

The forests of Big Sur are among the most impacted by Phytophthora ramorum, causal agent of Sudden Oak Death (SOD), in coastal California. Widespread mortality of key ecological species, such as oak (Quercus spp.) and tanoak (Lithocarpus densiflorus) threatens to alter the structure and dynamics of these forests. The distribution and magnitude of tree mortality was assessed across multiple scales over a 794 km² study area on the Pacific slope of the Santa Lucia Range in the Big Sur ecoregion. High-resolution (0.33 m) digital color aircraft imagery was used to detect and map the location of every dead tree which exhibited spectral characteristics of trees killed by SOD. Application of mortality density and basal area loss models in the GIS produced spatially-explicit estimates of 235,678 standing dead trees and 28,667 m² of basal area lost in the study area. The extensive mortality observed across the landscape supports data acquired on 175 1/20 ha long-term ecological monitoring plots established in the same area. Plot locations were based on fire history, land ownership, mortality and forest type. Tanoak and oak mortality levels were species and stem size dependant, often reaching over 50% in P. ramorum associated plots. High levels of coarse woody debris associated with overstory mortality were also recorded. On plots invaded by P. ramorum, 72% of living tanoaks were found to be infected; suggesting mortality levels will continue to increase. Quantification of the environmental impacts of this emerging disease in Big Sur will help guide management and restoration strategies.