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Risk of forest diseases given climate change: Case study of Phytophthora ramorum
S. J. FRANKEL (1), R. C. Cobb (2). (1) USDA Forest Service, Pacific Southwest Research Station, Albany, CA, U.S.A.; (2) Department of Plant Pathology, UC Davis, Davis, CA, U.S.A.

Since it was first recognized in the mid1990s,<i> Phytophthora ramorum </i>has killed millions of tanoak, <i>Notholithocarpus densiflorus,</i> and coast live oak (<i>Quercus agrifolia</i>) trees along the Pacific Coast in California and Oregon.  Symptom development, spread and mortality are linked to temperature and moisture conditions.   El Niño conditions that increase rainfall in the spring aid pathogen spread while intense heat coupled with low precipitation levels incite mortality. Data from aerial survey, permanent plots and other reports clearly demonstrate an ebb and flow in disease intensity.   Utilizing these apparent climatic relationships we present projections of how the pathogen will respond to climate change.   Cursory risk assessments and models indicate a range of outcomes but decreased rain and increased summer temperatures would decrease pathogen spread while increasing mortality of infected trees. Previous work has demonstrated that pathogen populations recover quickly following multi-year drought indicating that <i>P. ramorum</i> will be a persistent factor affecting forest ecosystem structure and function along the Pacific Coast. Climate driven fluctuations of pathogen dynamics are a characteristic of this disease which is insufficiently integrated into management plans.  

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