Examining the relationship between fire history and Sudden Oak Death patterns: A case study in Sonoma County1

Fire is often integral to forest ecology and can affect forest disease dynamics. Sudden Oak Death has spread across a large, fire-prone portion of California, killing large numbers of oaks and tanoaks and infecting most associated woody plants. Building on our earlier study of fire-disease dynamics, we examined spatial patterns of confirmed infections in relation to past fire history for a single county using a geographic information system (GIS). The region analyzed here is Sonoma County, where infections have been documented in past burn areas and exposure to the disease is thought to be extensive. We found that the disease is extremely rare inside recently burned areas (since 1950), although the relationship in this region is somewhat weaker than previous findings across a much larger area. This highlights how factors such as variation in vegetation, climate, and patterns of severity within burn areas are important to consider in the landscape pathology of Sudden Oak Death. Despite confirmation of earlier findings at a different scale of analysis, it remains to be seen whether the observed negative relationship between current infection locations and past fires is due to a fire-related mechanism, a surrogate of fire, and/or an artifact of the datasets used. Regardless, it is likely that interactions between the disease and fire will vary with local differences in host species composition, the stage of disease progression, and the scales of space and time used in analyses