Simard, M. 2010. Bark beetle-fire-forest interactions in the Greater Yellowstone Ecosystem. PhD dissertation, University of Wisconsin, Madison.

Bark beetles have affected extensive areas of western North America in the last decade. In this dissertation, the relationships between bark beetle outbreaks, wildfires, and conifer forests were investigated in the Greater Yellowstone Ecosystem (WY, USA). I first investigated the relative importance of plot- and landscape-level variables to explain landscape patterns of tree mortality caused by bark beetle outbreaks. Second, I used remote sensing and a chronosequence approach to quantify the recovery of lodgepole pine (Pinus contorta var. latifolia) aboveground biomass for 30 years following wildfires and severe mountain pine beetle (Dendroctonus ponderosae) outbreaks. Third, I used field surveys and modeling to determine the effects of mountain pine beetle outbreaks on forest fuels and on predicted fire behavior in a 35-year post-outbreak chronosequence that included undisturbed stands. Bark beetle outbreak severity was generally well predicted by landscape-level variables, especially by beetle pressure, i.e., the amount of and/or proximity to local eruptions at the beginning of the outbreak (3-4 years prior to sampling). Aboveground live biomass was greatly reduced after fire but recovered more rapidly than after bark beetle outbreaks. Recovery of post-disturbance aboveground biomass to pre-disturbance levels was relatively rapid, i.e., about 20-30 years. The major effect of mountain pine beetle outbreak on forest fuels was to reduce canopy bulk density by half compared to undisturbed stands. As a result, the probability of active crown fire was predicted to decrease for at least 35 years after disturbance. Twenty-five to 35 years after the outbreak, growth of surviving understory trees increased the vertical continuity of fuels between the ground and the tree crowns, and the model predicted an increase in the probability of passive crown fire. Simulated fire behavior was little affected by bark beetle disturbance when wind speed was either below 40 km/h or above 60 km/h, suggesting that fire weather may be a more important driver of fire behavior than fuel abundance and distribution. These results suggest that bark beetle outbreaks do not amplify subsequent fire activity in these forests and that post-disturbance management aimed at reducing the likelihood of active crown fire may not be needed.