Examining Mountain Pine Beetle Impacts on Coupled Fire/Vegetation/Atmosphere Behavior in Lodgepole Pine Stands Using FIRETEC

It is important to understand how disturbances such as insect or pathogen outbreaks may affect fire behavior in order to evaluate potential implications for fire-fighter safety, fuels management, and fire effects. Ecosystem disturbances such as infestations of mountain pine beetles in coniferous forests areas can drastically influence the behavior of fire following the disturbance. The influence of such disturbances depends heavily on the elapsed time between the outbreak and the ignition of the fire, the atmospheric and live and dead vegetation conditions at the time of the fire, and heterogeneity/continuity of the outbreak within the stand.

One approach to studying the influences of insect infestations on fire behavior in forests is through the use of coupled fire/atmosphere fire models such as FIRETEC. FIRETEC was used to examine the impacts of a mountain pine beetle outbreak on lodgepole pine forests as a function of time–since-outbreak, ambient wind speed, and the severity (wide spread or patchy) of the insect attack. The results of these simulations indicate that coupled fire/vegetation/atmosphere interaction dictates the nature of the fire behavior and that both local canopy-fuel conditions and stand structure changes must be considered. The changes in the stand structure modify atmospheric penetration into the forested region and turbulent mixing. The results also illustrate that depending on the outbreak heterogeneity, the nature of the fire/atmosphere coupling can be different. Changes in fire behavior also modify the wind fields around the fire, which subsequently feed back on the fire behavior. These results suggest that the impacts of such an outbreak include periods of both accelerated/intensified as well as decelerated/weakened fire behavior.