Potential Fire Behavior in Spruce Beetle-Induced Tree Mortality in Intermountain Spruce-Fir Forests
Spruce beetle- (Dendroctonus rufipennis Kirby [Coleoptera: Curculionidae]) induced tree mortality can increase fire intensity and severity resulting from changes to surface and aerial fuels. From inventoried fuel complexes, custom fuel models were developed. The endemic bark beetle condition class had greater amounts of live, available canopy fuel and canopy bulk density than either the epidemic and post epidemic condition classes. Epidemic bark beetle condition classes had the highest amounts of needle litter and1-hr time lag (0-0.64 cm diameter) fuel while the post-epidemic condition class had the highest amount live shrubs and non-woody plants. Fire behavior calculated with BehavePlus from the custom fuel models resulted in substantial differences in fire rates of spread and intensity for each spruce beetle condition class based on identical moisture scenarios and wind speeds. Rates of spread for epidemic and post-epidemic condition classes ranged between 2.0 – 2.9 and 3.0 – 4.5 times faster than the endemic condition class. Fireline intensities ranged from 4.1 – 5.0 times higher in the epidemic condition class and 6.6 – 8.8 times higher in the post-epidemic condition class compared to endemic condition class. An observed lack of overstory sheltering is attributed to increased fire behavior in epidemic and post epidemic condition classes and has a dominating affect on fire behavior. Post-epidemic condition class rates of spread and fireline intensities at identical midflame wind speeds were 1.7 and 3.3 times higher, respectively, than endemic parameters. Relatively, higher rates of spread (4.4 times) and fireline intensities (8.5 times), were observed between endemic and post-epidemic condition classes when calculated with 6.1 m wind speed adjusted for canopy sheltering. Custom fuel models developed for epidemic and post-epidemic classes showed similar results to selected established fuel models; however, no single fuel model exactly predicted fireline intensity and rate of spread for each of the custom fuel models developed.
Jorgensen, C.A. and M.J. Jenkins. 2010. Potential fire behavior in spruce beetle-induced tree mortality in Intermountain spruce-fir forests. Unpublished