Effects of Prescribed Fire on Tree Stress and Disease in Oak Dominated Forests

Incidents of Quercus decline have been driven by complicated interactions among factors such as temperature, drought, pathogenic fungi, and tree density, which operate at multiple time scales. In particular, past incidents of elevated tree mortality in response to drought in the highlands of Oklahoma were associated with biotic factors; specifically, the infection of Quercus species by canker-causing Biscogniauxia fungi. Much research has demonstrated the association between water stress and Biscogniauxia, however, little is known about the interactions between forest densification, water stress and fungal infection. I investigated the effects of disturbance regimes on Biscogniauxia prevalence at two different sites in Oklahoma-Pushmataha Wildlife Management Area (PWMA) and Okmulgee Wildlife Management Area (OWMA). Stands at PWMA were subjected to 4-year and 1-year fire return intervals, while OWMA stands received 2.5-year and 4.3-year fire return intervals. Utilizing a generalized linear mixed model (GLMM) I found that the incidence of Biscogniauxia was highest among units with a fire return interval of 4 years or greater. Additionally, trees exhibiting stress through canopy reduction had greater rates of infection. I measured stable C isotope ratio to investigate treatment effects on tree physiology, however, results suggested WUE was highest in units experiencing 4-yr and 1-yr fire return intervals at PWMA, counter to my expectations, while no effect was seen at OWMA. My observations illustrate the effectiveness of disturbance regimes on mitigating pathogenic attack and warrant further investigation to understand the effectiveness of fire regimes as a management strategy.Plant Biolog