Impact of the Mountain Pine Beetle on the Carbon Balance of Lodgepole Pine Stands in Western Canada

The current outbreak of the mountain pine beetle (MPB) has killed more than 9.2 million hectares (as of 2006) of lodgepole pine in British Columbia and is predicted to kill 80% of the pine volume by 2013. The implications of this outbreak on the carbon (C), water and energy balances of lodgepole pine forests is unknown. In fact, there have been no known reported measurements of net ecosystem productivity (NEP) of forest stands attacked by insects. This study used the eddy covariance (EC) technique to measure CO2, water vapour and sensible heat exchange above two MPB attacked lodgepole stands. Soil CO2 effluxes were measured using a portable dynamic chamber in trenched and non-trenched plots to determine soil autotrophic and heterotrophic respiration. The first attacked stand, located at Kennedy Siding (MPB-KS) (55° 06' 43''N, 122° 50' 23''W) was first attacked late in the summer of 2006. This almost pure lodgepole pine stand has a mean canopy height of 16 and an LAI of 1.38, and 90% of the trees were attacked early in the 2007 growing season. Below canopy EC measurements were made for 4 weeks in August/September 2007. The second stand, located on the edge of Crooked River Provincial Park (MPB-CR) (4° 28' 25''N, 122° 42' 43''W), which has secondary structure consisting mainly of spruce trees, was first attacked by MPB in 2003. It has a mean canopy height of 18 m, an LAI of 1.08, and all pine trees are dead. During the summer of 2007, EC measurements were also made for 3 weeks in both a naturally regenerating stand that was harvested in 1997 (Clearcut-97), and a 2-year-old salvage logged stand (Clearcut-06), in order to determine the effect of harvesting MPB attacked stands on the C budget.

During the growing season of 2007, MPB-KS remained a C sink (NEP ~ 0.5 g C m-2 day-1). MPB-CR was also a C sink during this growing season (NEP~ 0.7 g C m-2 day-1) showing the importance of secondary structure in sequestering C. We will present the results of 2007 EC measurements at MPB-KS and MPB-CR, as well as 3 weeks of EC measurements at Clearcut-97 and Clearcut-06. Results will focus on the effect of MPB on NEP and evapotranspiration as stands move from initial to late stages of an MPB attack. The C and water balances of the two MPB attacked stands will also be compared to that of the two harvested stands.