Surface Fire Intensity Influences Simulated Crown Fire Behavior in Lodgepole Pine Forests with Recent Mountain Pine Beetle-Caused Tree Mortality

Recent bark beetle outbreaks have had a significant impact on forests throughout western North America and have generated concerns about interactions and feedbacks between beetle attacks and fire. However, research has been hindered by a lack of experimental studies and the use of fire behavior models incapable of accounting for the heterogeneous fuel complexes. We populated the Wildland-Urban Interface Fire Dynamics Simulator with data from 11 field sites to investigate the effect of mountain pine beetle (MPB)-caused tree mortality on simulated crown fire behavior across a range of surface fire intensities. Simulations addressed fire behavior during a 1- to 2-year period after the initiation of the outbreak in which some proportion of the trees have been killed but no foliage has yet fallen. The effect of MPB-caused tree mortality on simulated crown fire behavior significantly changed as a function of surface fire intensity. The largest effects of mortality on crown fire behavior occurred at moderate levels of surface fire intensity, whereas diminished effects occurred at low and high levels of surface fire intensities. Our results suggest that increased crown fire potential immediately after bark beetle infestations is dependent on the fire intensity generated by the preoutbreak surface fuels complex.