PARENT SESSION
Oral Session #54: Fire Ecology -- Trees, forests, woodlands.
Presiding: E. Menges
Wednesday, August 7. 8:00 AM to 11:30 AM. Apache Meeting Room, TCC.
Searching for a general model of tree death in burned and unburned stands.
van Mantgem, Phillip*,1, Stephenson, Nathan1, 1 U.S.G.S./B.R.D., Three Rivers, CA
ABSTRACT- Currently, models for predicting probabilities of tree death use different sets of predictive variables for burned and unburned stands. Growth rate, a measure that integrates many of the variables related to carbon balance within individual trees, is often used to predict mortality in unburned stands. In contrast, death in burned stands is modeled as a function of fire-caused damage, most commonly the amount of crown scorch. We sought to narrow this conceptual gap among models of tree death by determining (1) whether growth rate, in addition to crown scorch, is a significant predictor of tree death in burned stands, and (2) whether a single, simple model could predict tree death in both burned and unburned stands. For white fir (Abies concolor) in the Sierra Nevada of California, USA, we found that radial growth rate is a significant predictor of post-fire survival. Growth rate was also found to be better than stem size as a predictor of post-fire mortality. The relative importance of growth rate as a predictor of post-fire mortality increased if we considered only those trees that sustained low to moderate amounts of crown scorch. We tested the ability of the model of tree death in burned stands, with the coefficient for crown scorch set to zero, to predict tree death in an unburned stand. The model consistently overestimated the mortality rate for unburned trees. A separate model, using data only from trees that suffered low amounts of crown scorch, was a better predictor of mortality in the unburned stand. While failing to create a general model of tree death, our findings underscore the idea that mortality in disturbed and undisturbed stands are not fundamentally different processes, and that gaining a mechanistic understanding of tree death will depend partly on descriptions of tree carbon budgets.
KEY WORDS: disturbance, fire effects, mortality models, radial growth