The effects of sudden oak death and wildfire on forest composition and dynamics in the Big Sur Ecoregion of Coastal California

Abstract

Sudden oak death (SOD), caused by Phytophthora ramorum, is an emerging forest disease associated with extensive tree mortality in coastal California forests (Rizzo et al. 2005). P. ramorum is a generalist pathogen that infects many hosts, but hosts differ in their ability to transmit the disease and in the impacts caused by the disease. In coast redwood forests, tanoak (Notholithocarpus densiflorus) is the main host dying from SOD and the main source of pathogen inoculum. SOD leads to compositional changes in these habitats through selective mortality of tanoak. The effect of SOD on forest dynamics does not happen in isolation from other disturbances. Rather, fire is an important part of the natural disturbance regime in California's coastal forests. Elevated mortality by the disease may lead to increased fuel loads in these forests, leading to the potential for SOD to interact with wildfire severity (Valachovic et al. 2011). In 2008, wildfires in SOD-impacted forests presented a natural experiment to examine the interaction between these two disturbances (Metz et al. 2011). We used a long-term network of forest monitoring plots in the Big Sur region of central California to examine the separate and joint impacts of an emergent forest disease and wildfire on forest dynamics and diversity. The network contains burned and unburned areas, and areas with and without P. ramorum. Specifically, we asked: 1) Did redwood stands that became infested by P. ramorum differ in species composition from uninfested areas? 2) How is P. ramorum changing species composition in redwood forests? 3) How did mortality from SOD impact fire severity in burned areas? 4) Was fire mortality selective by species?

Parent Publication

• Proceedings of the coast redwood forests in a changing California: A symposium for scientists and managers

Citation

Metz, Margaret R.; Frangioso, Kerri M.; Meentemeyer, Ross K.; Rizzo, David M. 2012. The effects of sudden oak death and wildfire on forest composition and dynamics in the Big Sur Ecoregion of Coastal California. In: Standiford, Richard B.; Weller, Theodore J.; Piirto, Douglas D.; Stuart, John D., tech. coords. Proceedings of coast redwood forests in a changing California: A symposium for scientists and managers. Gen. Tech. Rep. PSW-GTR-238. Albany, CA: USDA-Forest Service, Pacific Southwest Research Station. pp. 373-376.