Abstract

EFFECTS OF FIRE ON TREE PHYSIOLOGY AND MECHANISMS FOR RECOVERY

by

Ryan Allan Salladay

As wildfires continue to become larger and more frequent, there is a substantial impact on tree health and resilience. Low and moderate severity fires can cause damage to the xylem and vascular cambium. However, the relative effects of fire on these tissues remain poorly understood. It is important to identify the mechanisms of fire-induced tree mortality, so we can better predict the consequences of large wildfires on forests. Furthermore, many trees are adapted to fire and survive moderate severity burns. In those cases, it is critical to understand the anatomical and physiological mechanisms which allow trees to recover from fires. This may occur in the form of tradeoffs in carbon allocation between thick cell walls, many cell walls, or parenchyma fraction. To better understand the effects of fire on tree physiology and mechanisms for tree recovery, I used a combination of laboratory experiments and anatomy studies. In Chapter one, I used an oven to simulate the hot, dry air experienced by trees during fire. This temperature treatment was used to identify the effect of heat on xylem and cambium function in Sequoia sempervirens stems. In Chapter two, I conducted a similar heat experiment, but also integrated a dehydration treatment. By combining heat and dehydration in the lab, my goal was to disentangle the effects of fire and drought, which often co-occur. This experiment was conducted on four diverse tree species. In Chapter three, I used partial cross sections of Pinus ponderosa to identify the changes in xylem anatomy caused by fire scars. I measured xylem traits in rings before and after the fire scar to determine changes in anatomy and infer physiological tradeoffs during recovery. Together, these chapters integrate the impacts of fire on tree physiology and explore the tissues that allow tree to recover from fire. Ultimately, this research can be used to predict tree mortality and help inform land management practices.