PS 32-38
Forest resprouting responses to interacting disturbances: Wildfire and sudden oak death in Big Sur, CA
Novel interactions between multiple disturbances may impact regeneration trajectories, leaving lasting legacies on community structure and function. Sudden Oak Death, caused by Phytophthora ramorum, is an emerging nonnative disease associated with widespread tree mortality in coastal forests of California and Oregon. In disease-impacted redwood-tanoak forests, wildfire also shapes forest structure and composition with the dominant tree species resprouting rapidly after fire. These tree species differ in their resprouting capacities, their effectiveness as a host for P. ramorum, and their susceptibility to both fire and disease. In 2006, 280 plots were established to monitor the progression of Sudden Oak Death in the Big Sur region of central California. The 2008 Basin and Chalk fires burned across Big Sur impacting both infested and disease-free plots and providing an opportunity to investigate impacts of multiple disturbances on forest regeneration trajectories and subsequent disease dynamics. In 2009, 2010, and 2013, 40 burned and unburned forest plots were re-sampled to assess tree mortality, pathogen presence, microclimatic conditions, and post-disturbance regeneration, including resprouting vigor and seedling recruitment. We investigated how prior stand structure and disease history influence post-fire resprouting, and in turn, whether the extent and pattern of resprouting hosts impact post-fire disease dynamics.
Results/Conclusions
Five years after the fire, 90% of plots that were infested pre-fire have been reinvaded by P. ramorum. Tanoak and bay laurel, the dominant sporulating hosts for the pathogen, suffered greater aboveground post-fire mortality compared to nonsporulating hosts, but these species have resprouted vigorously. Resprouting volumes and counts were significantly greater in burned plots, compared to undisturbed and infested, unburned plots. Uninfested, burned plots showed increased resprouting in redwood and tanoak, compared to infested, burned plots. For individual trees in burned plots, resprouting volume and number was significantly related to a tree’s pre-fire size (total basal area); whereas in unburned areas, resprouting vigor was significantly correlated with the loss of plot-level basal area. This suggests that pre-fire stand structure and demography strongly influence the extent of post-fire regeneration, but in response to disease, resprouting is more strongly predicted by local mortality levels. Preliminary microclimatic data suggest that, in burned areas, large resprouting clusters foster decreased peak mid-day summer temperatures and increased local humidity, compared to nearby exposed areas. The pattern of resprouting in disturbed forests may determine future disease dynamics not only through the spatial distribution of hosts, but also by creating crucial microsites for the pathogen in post-fire environments.