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.
Tree vulnerability to fires: thermal tolerance of live bark cell populations.
Dickinson, Matthew*,1, Johnson, Edward2, 1 USDA Forest Service, Delaware, Ohio, mbdickinson@fs.fed.us2 University of Calgary, Calgary, Alberta, Canada
ABSTRACT- Tolerance of live bark tissues for temperature regimes such as those experienced by trees during fires differed trivially among Populus tremuloides (aspen), Picea englemannii (Englemann spruce), and Pseudotsuga menziesii (Douglas fir), common species of the Canadian Rocky Mountains. As well, there was no evidence of differences between the growing and dormant seasons for either aspen or Englemann spruce, the two species for which seasonal comparisons were made. Tree trunks are heated during fires by a transient process; vascular cambium temperatures rise during the residence time of the flames and then fall after the bark surface has cooled. We quantified live bark thermal tolerance with estimates of the parameters of a cell survival model. The model includes the processes thought to underlie the effects of elevated temperatures on populations of cells (H. Jung, 1986, Radiation Research 106:56-72). Model parameters were estimated with cell count data from tissues subjected to a range of exposure times at constant elevated temperatures in a water bath. We validated the model for use in fire effects modeling by comparing predicted with observed cell survival after bark tissues were exposed to transient temperature regimes. Finally, species and seasons were compared in the context of vascular cambium temperature regimes generated for trees of a range of bark thicknesses by a one-dimensional conduction heat-transfer model. The cell survival model was validated for aspen, Englemann spruce, and Douglas fir but gave biased predictions for Pinus contorta (lodgepole pine). Our results suggest that a comparison among tree species growing in ecosystems with very different fire regimes or climates may be more likely to reveal differences in thermal tolerance than a comparison among species within a single ecosystem.
KEY WORDS: fire, thermal, tolerance, kinetics