Landscape carbon trajectories after spruce budworm outbreaks in Canada’s Eastern boreal forest: effects of salvage intensity and wood-use pathways

Abstract Context Salvage biomass harvesting is increasingly recognized as a strategic approach to reduce emissions associated with spruce budworm (SBW) damage in eastern Canada by diverting biomass that would otherwise decompose in forests toward bioenergy and harvested wood products (HWP). However, its effects on overall system carbon dynamics remain poorly understood. Objective We assessed how SBW-related salvage harvesting influences long-term (2010–2110) forest-sector carbon dynamics in the Côte-Nord region of Québec, Canada, considering net sector production (NSP), which is the sum of net carbon sequestration by ecosystem and HWP less operational emissions (harvesting, forwarding, transport, sawing, chipping, pelletization). This study evaluates the biophysical carbon balance and sector-level carbon dynamics of salvage harvesting, without accounting for substitution. Method We used the LANDIS-II model, its Forest Carbon Succession extension, and additional modules to simulate wind, fire, and SBW disturbances under multiple climate pathways. A no-additional-salvage reference (S0) was compared to increasing salvage areas (S1–S3) of dead snag stems. All additional salvaged biomass was directed to one of three pathways: bioenergy, sawnwood with a 35-year half-life, or sawnwood with a 60 year half-life. Results Salvage harvesting had minimal impact on ecosystem carbon pools but slightly reduced heterotrophic respiration by removing decomposing deadwood. The net carbon outcome depended strongly on product pathway: directing salvaged biomass to bioenergy resulted in immediate emissions and negative balance relative to the reference scenario; short-lived sawnwood (35-year half-life) increased HWP storage but accumulated decomposition emissions over time, also resulting in negative carbon balance; only long-lived sawnwood (60-year half-life) reduced total emissions sufficiently to approach/exceed carbon neutrality—and only under warmer climate scenarios (RCP4.5–RCP8.5) by late century. Operational emissions from harvesting, transport, and processing remained small relative to ecosystem and HWP carbon fluxes. Conclusions Within the modeled system boundary (excluding substitution effects), the forest-sector carbon outcome of salvage harvesting depended strongly on target area, product type and their longevity; however, any benefits for reduced carbon emissions are likely to come from substitution effects unless warming dramatically increases decomposition and HWP have above-expected half-lives.