Carbon Dynamics in Central US Rockies Lodgepole Pine Type after Mountain Pine Beetle Outbreaks

Abstract

Mountain pine beetle-caused tree mortality has substantially changed live tree biomass in lodgepole pine ecosystems in western North America since 2000. We studied how beetle-caused mortality altered ecosystem carbon (C) stocks and productivity using a central US Rockies age sequence of ecosystem recovery after infestation, augmented with growth-and-yield model simulations. Field measurements showed that total C stocks were reduced by beetle outbreaks, although differences compared with undisturbed stands were not easily distinguished. Simulations with outbreaks showed long-term C losses of 1–30%. Field data indicated that aboveground C productivity was reduced among plots infested within 25 years of measurements, but productivity levels of plots with older infestations were indistinguishable from those of undisturbed plots. Simulations indicated that outbreaks reduced C productivity for 20 – 60 years, but rates recovered such that 100-year postoutbreak averages were similar among infested and undisturbed stands. Simulations also showed that C dynamics are affected by outbreak severity and that C productivity might be stimulated by outbreaks relative to that of undisturbed stands. Outbreaks redistributed C from live (sinks) to dead pools (sources), but slow decomposition of snags combined with recovered tree growth resulted in resilience of aboveground C stocks.