Masters Thesis

Predicting sudden oak death transmission hosts in Redwood National and State Parks using ecological niche models

Phytophthora ramorum, an aggressive introduced plant pathogen, has caused the death of several million tanoak (Lithocarpus densiflorus) and oak (Quercus spp.) trees throughout coastal forests of California and Oregon. In the United States, P. ramorum infections occur in 14 contiguous coastal California counties, from Monterey to Humboldt, and in Curry County, Oregon. Currently, P. ramorum has not been detected in the forests of Redwood National and State Parks (RNSP), however, the pathogen occurs in close proximity. An infestation in Curry County, Oregon is 17 km north of RNSP’s Jedediah Smith State Park, and a recent detection near Redwood Valley (Humboldt County, California) is less than 8 km southeast of the Parks’ southern border. This closeness is concerning because much of RNSP is vulnerable to P. ramorum infestation. Using Maxent, a niche-based modeling program, I determined that 60% of RNSP has the presence of at least one key pathogen-transmission species: California bay (Umbellularia californica), tanoak, and Pacific rhododendron (Rhododendron macrophyllum). Tanoak, which is also highly susceptible to P. ramorum-induced mortality, occurred in 47% of RNSP. All species’ models showed sufficient sensitivity and accuracy to create reliable distribution maps at 30 m x 30 m resolution. These data will be used in future efforts to predict potential P. ramorum disease spread throughout the Parks.