Ecosystem response to the repeated interaction of disease and fire

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This award focuses on the long-term study of interactions between fire and a forest disease, Sudden Oak Death, in the Big Sur region of California. While fire is an important part of the ecology of healthy California forests, Sudden Oak Death is a recently introduced disease that has killed millions of trees in coastal California over the past 20 years. Disease-killed trees serve as fuel and may increase the risk for the ignition, spread, and increased intensity of wildfires. While fire and disease both cause extensive tree death, each disturbance type results in different types of impacts and recovery of forests. To that end, the proposed research seeks to determine how multiple, and altered, disturbances interact to determine the composition of the regenerating plant community and shape the severity, frequency, and timing of future disturbances. The threat of wildfire plays a major role in policy decisions in many communities throughout California and the western United States. The cost of fighting wildfires has increased dramatically as more people live in locations in and near forests. Understanding how disease and fire interact to impact forests is important in fighting fires, protecting communities, and in aiding the recovery of forests after catastrophic fire and disease outbreak.Disease-fire interactions in Big Sur forests will be examined across an 80,000 ha plot network that was established in 2006 to study Sudden Oak Death. Large fires burned across the plot network in 2008 and in 2016, providing an opportunity to study disease-fire interactions at a very large scale. Initial results from the Big Sur plot network indicate that these forest ecosystems are moving toward novel disturbance regimes with complex interactions between disease and fire, impacting tree and shrub species that are otherwise resilient to either disturbance. Increases in wildfire severity due to the presence of disease can increase mortality of tree species not susceptible to disease, alter forest assemblages and biogeochemical cycles, and ultimately, create the context for how the joint disturbances of fire and disease and will re-emerge across the landscape. The research approach includes monitoring the vegetation, pathogens, and soil nutrients of the long-term field plots, laboratory quantification of pathogens, as well as statistical modeling. The proposed research plan anticipates that the dramatic tree mortality due to Sudden Oak Death in Big Sur will continue for many years, thereby influencing fuel loading and subsequently natural fire regimes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.