The Impact of the Woolsey Fire on the Fungus Botryosphaeria dothidea

Southern California suffered a six-year drought in 2012 through 2018 during which the laurel sumac, Malosma laurina, experienced water stress and the fungus Botryosphaeria dothidea began to kill this plant, causing a massive dieback of this keystone chaparral species in the Santa Monica Mountains. Botryosphaeria is an opportunistic endophytic fungus that invades the xylem of woody type plants and waits till the plant starts to experience stress to proliferate. In November of 2018, the Woolsey fire burned up to 96,000 acres of vegetation. I ran tests at two sites on the Pepperdine University campus, the Baxter Ridge Site which had burned and unburned plants, and the Via de Casa Site, also known as the Dieback site, which had resprouts and seedlings. My hypothesis was the fungus Botryosphaeria would be prevalent at the Dieback site after the fire and that a healthy plant would be better able to fight off the fungus. After the fire I isolated nine samples respectively from seedlings, resprouts, and adults of the M. laurina for the presence of the fungus. I inoculated stem segments from resprouts and adults at both sites to determine the growth rate of the fungus. Other tests were done to determine the amount of water stress that M. laurina was experiencing, including measurements of midday and predawn water potential and gas exchange parameters. Results indicated the fungus was present at both sites in adults, resprouts and seedlings. Growth rates of the fungus were greater in resprouts at the Dieback site than in unburned adults at the Baxter site. Water stress was greater in the seedlings than for the adults and resprouts at both sites; after an unexpected summer rain this year adults and resprouts showed little water stress through mid-July, which may keep the fungus at bay this year