2022/09/12 by Bates, Gabriella, Cohen, Gabrielle, Martos, Perla +1
#California bay laurel (Umbellularia californica) #Phytophthora ramorum #compound disturbance #disturbance #fire #tanoaks (Notholithocarpus densiflorus)
paper · doi:10.21973/n3c37d
Disturbances, both biotic and abiotic, play an integral role in shaping the species composition of ecological communities. Recently, the compounding disturbances of fire and sudden oak death have affected forests in California’s Big Sur region. Sudden oak death (SOD), caused by the non-native pathogen Phytophthora ramorum, has led to large-scale mortality in tanoak (Notholithocarpus densiflorus) populations and finds reservoirs for transmission in California bay laurels (Umbellularia californica). In this study, we investigated how the post-fire regrowth rates of tanoak and bay laurels in SOD-infected forests are affected by individual tree burn severity and surrounding heterospecific community density, as well as how the surrounding tanoak and bay laurels densities affect tanoak regrowth. We measured trunk scorch height and soil ash depth to determine tree burn severity, number, and height of the tallest resprout of focal trees as a proxy for growth rate; total trees in the 10-meter radius as a proxy for density; and the number of tanoaks and bay laurels (key P. ramorum hosts) in the 10-meter radius to investigate the effect of host density. We found that a higher scorch height was associated with taller resprouts, and heterospecific density decreased resprout height. Although tanoak regrowth positively correlates with increased burn severity, bay laurels were found to have a faster regrowth rate than tanoaks, indicating that fire is insufficient at decreasing P. ramorum transmission throughout the ecosystem and may lead to further bay laurel expansion in SOD-impacted forests.