Background: Mountain pine beetle (MPB) is a native disturbance agent across most pine forests in the western US. Climate changes will directly and indirectly impact frequencies and severities of MPB outbreaks, which can then alter fuel characteristics and wildland fire dynamics via changes in stand structure and composition. To investigate the importance of MPB to past and future landscape dynamics, we used the mechanistic, spatially explicit ecosystem process model FireBGCv2 to quantify interactions among climate, MPB, wildfire, fire suppression, and fuel management under historical and projected future climates for three western US landscapes. We compared simulated FireBGCv2 output from three MPB modules (none, simple empirical, and complex mechanistic) using three focus variables and six exploratory variables to evaluate the importance of MPB to landscape dynamics.

Results: We found that inclusion of MPB (empirical or mechanistic) in the simulations significantly changed past and future landscape dynamics and that the mechanistic MPB module had more cross-scale interactions that increased variability, and perhaps realism, of simulation results. We also evaluated impacts of fire and fuel management on MPB dynamics and found that fire suppression influenced fuel loadings more than MPB disturbance, but at a landscape scale, most fuel treatment programs did little to change fuel loadings, MPB dynamics, and burned area, except under high fire suppression.

Conclusions: Synergistic interactions of climate, MPB, and wildfire catalyzed landscape-scale changes in vegetation distributions, fuels, and fire regimes in FireBGCv2 simulations. Models that simulate climate change on pine-dominated landscapes may be improved by including mechanistic MPB simulations to account for potentially important ecological interactions.