Estimating the reduction in gross primary production due to mountain pine beetle infestation using satellite observations

The impact of disturbance on national and global forest carbon budgets is considered large enough to shift forests into acting as carbon sinks or sources. While the role of fire on the landscape and its impact is relatively well understood, the role of insect infestation is less well known. The ongoing outbreak of mountain pine beetle (Dendroctonus ponderosae) in western Canada is impacting over 9.2 million ha of forest as of 2006. Using satellite-derived (Moderate Resolution Imaging Spectroradiometer (MODIS)) annual estimates of gross primary production (P(g)), in combination with survey data indicating infestation extent and severity, the reduction in P(g) attributable to this major disturbance is estimated. Results indicate that the infestation between 2002 and 2005 resulted in a reduction in the rate of carbon accumulation of between 60-100 g Cm(-2) year(-1), which corresponds well with previously modelled values, reducing the pre-outbreak P(g) of the stands by approximately 15-20%, with productivity losses generally proportional to the locally accumulated severity of insect activity. Continued monitoring using MODIS based approaches may offer ongoing opportunities to estimate the landscape-level rates of recovery from the outbreak.