Simulated impacts of mountain pine beetle and wildfire disturbances on forest vegetation composition and carbon stocks in the Southern Rocky Mountains

摘要

Forests play an important role in sequestering carbon and offsettinganthropogenic greenhouse gas emissions, but changing disturbance regimes maycompromise the capability of forests to store carbon. In the Southern RockyMountains, a recent outbreak of mountain pine beetle (extit{Dendroctonus ponderosae}; MPB) has causedremarkable levels of tree mortality. To evaluate the long-term impacts ofboth this insect outbreak and another characteristic disturbance in theseforests, high-severity wildfire, we simulated potential changes in speciescomposition and carbon stocks using the Forest Vegetation Simulator (FVS).Simulations were completed for 3 scenarios (no disturbance, actual MPBinfestation, and modeled wildfire) using field data collected in 2010 at 97plots in the lodgepole-pine-dominated forests of eastern Grand County,Colorado, which were heavily impacted by MPB after 2002. Results of thesimulations showed that (1) lodgepole pine remained dominant over time in allscenarios, with basal area recovering to pre-disturbance levels 70–80 yrafter disturbance; (2) wildfire caused a greater magnitude of change than didMPB in both patterns of succession and distribution of carbon among biomasspools; (3) levels of standing-live carbon returned to pre-disturbanceconditions after 40 vs. 50 yr following MPB vs. wildfire disturbance,respectively, but took 120 vs. 150 yr to converge with conditions in theundisturbed scenario. Lodgepole pine forests appear to be relativelyresilient to both of the disturbances we modeled, although changes inclimate, future disturbance regimes, and other factors may significantlyaffect future rates of regeneration and ecosystem response.