Influence of recent bark beetle outbreak on fire severity and postfire tree regeneration in montane Douglas-fir forests

Brian J. Harvey, Daniel C. Donato, William H. Romme, and Monica G. Turner

This study was conducted to asses the impact bark beetles has on wildfires and how quickly they spread along with tree regeneration after the fire had occurred. These researchers looked at the Gunbarrel fire of 2008, which took out 27,000 hectares of Douglas-fir (pseudotsuga menzeisii) dominant wilderness. This area experienced a bark beetle outbreak 4-13 years before the fire occurred and the majority of the trees were dead or dying with their needles dropped. There were 85 plots sampled for stand structure pre-fire and severity of bark beetle outbreak. It was found that fire severity was directly correlated with topography and burning conditions. Regeneration of Douglas-firs after the fire was low with no tree seedlings in 65% of plots. Tree seedlings were abundant in plots with low fire severity that also had low outbreaks of bark beetles. There is no link between the severity of burn and outbreak of bark beetles, but together they have high disturbance level.

To answer these questions about Douglas-fir populations in lower mountainous regions, researchers had to use reports of acts, behaviors, and events because they are looking at the behaviors of species in relation to a disease and fire.

To conduct this study, 85 plots were sampled in the mid Rocky mountain eco-region. Plot samples began in 1995 to measure bark beetle outbreaks and peaked in the early 2000’s. Most trees (98.5%) were killed by bark beetles before the fire began. To sample plots, bark was tested from every tree taller than 1.4 m and analyzed using Spearman’s rank correlation test between each quantitative metric of fire severity and beetle-killed area in all plots.

Harvey, Brian J., et al. “Influence of recent bark beetle outbreak on fire severity and postfire tree regeneration in montane Douglas‐fir forests.” Ecology 94.11 (2013): 2475-2486.