Physiological Stress and Ethanol Accumulation in Tree Stems and Woody Tissues at Sublethal Temperatures from Fire

The lethal temperature limit is 60 degrees Celsius (degrees C) for plant tissues, including trees, with lower temperatures causing heat stress. As fire injury increases on tree stems, there is an accompanying rise in tissue ethanol concentrations, physiologically linked to impaired mitochondrial oxidative phosphorylation energy production. We theorize that sublethal tissue temperatures of 30 degrees C to 60 degrees C cause physiological changes to (a) oxygen supply, (b) membrane function, or (c) enzyme activity that individually or simultaneously create stress by impairing aerobic respiration and inducing ethanol synthesis. Accumulating ethanol dissipates via diffusion, sapflow, and metabolism, but the ability of these processes to decrease ethanol depends on what temperatures and physiological stress mechanism(s) the tissues and whole trees experience. The synthesis and dissipation interactions determine postfire tissue ethanol concentrations. Wildfire trends positively with temperature and drought, and all are projected to increase in western US forests and elsewhere globally, increasing the importance of understanding tree sublethal heat stress from fire.