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1 Phytophthora ramorum (causal agent of sudden oak death) is an emerging generalist pathogen in coastal forests of California and Oregon, USA, that causes lethal stem infections on oaks (Quercus spp.) and tanoak (Lithocarpus densiflorus) as well as nonlethal foliar infections on a broad range of trees and shrubs. 2 We studied P. ramorum over its known range in coastal redwood forests to determine forest compositional variables that are important to its epidemiology within the geographical area that it has already invaded. Redwood forests are dominated by coast redwood (Sequoia sempervirens), tanoak and California bay laurel (Umbellularia californica). 3 A total of 120 permanent plots (500 m² each) were established in redwood forests at 12 sites within the main epidemic area in California. Over 5000 trees were mapped and examined for the presence of P. ramorum during spring 2002 and …