“More research is required to fully understand fire behavior over time following a mountain pine beetle attack. Nonetheless, the extensive epidemic now occurring is precipitating enormous changes in fuel structure over large areas in Colorado and Southern Wyoming, through changes in the condition and arrangement of the forest biomass (which is fuel for forest fires)” (Kaufmann, 2012, p. 8).
These changes in the arrangement of the forest biomass can affect many aspects of a forest fire such as the type of fire (ground or crown fire), intensity, frequency, and the duration of the fire. One of the first things to happen after a pine tree is killed by the Mountain Pine Beetle is all of the pine needles dry out and change to a red or yellow color. This creates large amounts of very dry fine fuel in the canopy of the trees and can increase the risk of crown fires especially under less extreme fire weather conditions (Kaufmann, 2012, p 9).
Once all needles have fallen from dead trees, usually within four years of tree mortality (Klutsch et al. 2009), it isgenerally believed probability of crown fire ignition is low because there are no needles to cause fire to spread through the canopy (Page and Jenkins 2007b, Jenkins et al. 2008).” (as cited in Pelz, 2011, p. 6).
Over time the beetle killed trees will begin to fall and decay, however it is unknown how long this will take. Before a majority of the trees begin to fall but after the needles have fallen, fire behavior can be dramatically different than the other stages of a beetle infestation. The trees on the right side in the picture below shows this stage.
Although there is a large amount of dry fuel available in the trees, it is unlikely to ignite without fine fuels and fires that do occur are likely to be less intense surface fires unable to reach the canopy (Kaufmann, 2012, p. 9). In a study by Mitchell and Preisler 80% of killed trees fell within 10 years, however in British Columbia the Forest Practices Board found “on average 45% (with a range of 0 – 80%) of trees were still standing 25 years after they were killed by MPB” (as cited by Pelz, 2011, p. 6-7). After a majority of trees do begin to fall there will be a large increase in coarse surface fuels that may become an increase fire hazard over time with the growth of a new understory that can provide fine fuels as an ignition source (Pelz, 2011, p. 7).
Kaufmann, Merrill, Gregory Aplet, Michael Babler, and William Baker. 2012 The Status of Our Scientific Understanding of Lodgepole Pine and Mountain Pine Beetles – A Focus on
Forest Ecology and Fire Behavior. Rep. N.P.: n.p., n.d. The Nature Conservancy. Web. 10
Pelz, Kristen A. EFFECTS OF MOUNTAIN PINE BEETLE ON FOREST STRUCTURE AND FUEL LOAD 25-30 YEARS AFTER AN OUTBREAK IN WESTERN COLORADO. Thesis. Colorado State University Fort Collins, Colorado, 2011. N.P.: n.p., n.d. Print.