PARENT SESSION
Oral Session #55: Fire Ecology. Presiding: M. Moritz.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas H.

Tree death in surface fires: modeling the effects of elevated temperatures on the vascular cambium.

Dickinson, Matthew¹, Johnson, Edward¹, ¹

ABSTRACT- When surface fires spread past trees, vascular cambium in roots is heated by smoldering combustion, vascular cambium in the bole of the tree is heated by the flames, and buds and foliage in tree crowns are heated by the buoyant plume of hot gases above the flames. Elevated temperatures within these tissues cause cell mortality, tissue necrosis, and tree death. Vascular cambium necrosis in the boles of trees is the most important reason for tree death when surface fire intensity is low and/or tree crowns are elevated and when smoldering combustion in surface organic layers is minimal. The current model of bole vascular cambium necrosis assumes a threshold temperature for necrosis (60°C). However, temperature effects on tissues occur continuously above a certain minimum temperature (approximately 40°C) and their rates increase rapidly with temperature. Here, we model the continuous process of aspen (Populus tremuloides) and spruce (Picea englemannii) vascular cambium cell mortality during temperature regimes characteristic of those at the vascular cambium during surface fires. The model approximates the thermal kinetics processes by which elevated temperature are thought to cause their effects and is parameterized with data on aspen and spruce cell mortality at constant temperatures. The model makes good predictions of cell mortality (R² = 0.84, P < 0.0001), and, thus, provides a means by which fire behavior can be linked with fire effects on the vascular cambium.

KEY WORDS: fire effects, vascular cambium cell mortality, thermal kinetics, tree death