Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 13, 5277-5295, 2016
http://www.biogeosciences.net/13/5277/2016/
doi:10.5194/bg-13-5277-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
22 Sep 2016
Modelling long-term impacts of mountain pine beetle outbreaks on merchantable biomass, ecosystem carbon, albedo, and radiative forcing
Jean-Sébastien Landry1,6, Lael Parrott2, David T. Price3, Navin Ramankutty4, and H. Damon Matthews5 1Department of Geography, McGill University, Montréal, Canada
2Earth and Environmental Sciences and Biology, Irving K. Barber School of Arts and Sciences, University of British Columbia, Kelowna, Canada
3Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre, Edmonton, Canada
4Liu Institute for Global Issues and Institute for Resources, Environment, and Sustainability, Universityof British Columbia, Vancouver, Canada
5Department of Geography, Planning and Environment, Concordia University, Montréal, Canada
6Currently at the Department of Geography, Planning and Environment, Concordia University, Montréal, Canada
Abstract. The ongoing major outbreak of mountain pine beetle (MPB) in forests of western North America has led to considerable research efforts. However, many questions remain unaddressed regarding its long-term impacts, especially when accounting for the range of possible responses from the non-target vegetation (i.e., deciduous trees and lower-canopy shrubs and grasses). We used the Integrated BIosphere Simulator (IBIS) process-based ecosystem model along with the recently incorporated Marauding Insect Module (MIM) to quantify, over 240 years, the impacts of various MPB outbreak regimes on lodgepole pine merchantable biomass, ecosystem carbon, surface albedo, and the net radiative forcing on global climate caused by the changes in ecosystem carbon and albedo. We performed simulations for three locations in British Columbia, Canada, with different climatic conditions, and four scenarios of various coexisting vegetation types with variable growth release responses. The impacts of MPB outbreaks on merchantable biomass (decrease) and surface albedo (increase) were similar across the 12 combinations of locations and vegetation coexistence scenarios. The impacts on ecosystem carbon and radiative forcing, however, varied substantially in magnitude and sign, depending upon the presence and response of the non-target vegetation, particularly for the two locations not subjected to growing-season soil moisture stress; this variability represents the main finding from our study. Despite major uncertainty in the value of the resulting radiative forcing, a simple analysis also suggested that the MPB outbreak in British Columbia will have a smaller impact on global temperature over the coming decades and centuries than a single month of global anthropogenic CO2 emissions from fossil fuel combustion and cement production. Moreover, we found that (1) outbreak severity (i.e., per-event mortality) had a stronger effect than outbreak return interval on the variables studied, (2) MPB-induced changes in carbon dynamics had a stronger effect than concurrent changes in albedo on net radiative forcing, and (3) the physical presence of MPB-killed dead standing trees was potentially beneficial to tree regrowth. Given that the variability of pre-outbreak vegetation characteristics can lead to very different regeneration pathways, the four vegetation coexistence scenarios we simulated probably only sampled the range of possible responses.

Citation: Landry, J.-S., Parrott, L., Price, D. T., Ramankutty, N., and Matthews, H. D.: Modelling long-term impacts of mountain pine beetle outbreaks on merchantable biomass, ecosystem carbon, albedo, and radiative forcing, Biogeosciences, 13, 5277-5295, doi:10.5194/bg-13-5277-2016, 2016.
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We simulated mountain pine beetle (MPB) outbreaks under four scenarios for the presence and growth release strength of non-attacked vegetation, and found that: (1) impacts on ecosystem carbon and radiative forcing varied greatly across the four scenarios; (2) the global climatic impact from the current outbreak in British Columbia, Canada, seemed smaller than one month of anthropogenic CO2 emissions; and (3) MPB-killed dead standing trees might hasten post-outbreak vegetation recovery.
We simulated mountain pine beetle (MPB) outbreaks under four scenarios for the presence and...
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