Abstract

The next major eastern spruce budworm (Choristoneura fumiferana) outbreak is likely to begin impacting the forests of the northeastern US over the next few years. More than 4.7 million ha of forest and 94.8 million Mg of carbon in spruce (Picea spp.) and balsam fir (Abies balsamea) are at risk. Vegetation shifts in at-risk forest stands are likely to occur as a direct result of mortality caused by spruce budworm and through post-outbreak salvage harvest operations designed to minimize economic impact. Management interventions have short-term and long-term consequences for the terrestrial carbon budget and have significant implications for the role of the region’s forests as a natural climate solution. We used regional forest inventory data and 40-year growth and harvest simulations from the USDA Forest Service Forest Vegetation Simulator to quantify a range of forest carbon outcomes for alternative silvicultural interventions in the northeastern US. We performed a life cycle assessment of harvested wood products, including bioenergy, to evaluate the full greenhouse gas (GHG) emissions consequences of salvage and business as usual silvicultural scenarios across a range of stand risk profiles in the presence and absence of spruce budworm attack. Salvaging dead trees in the most at-risk stands tends to produce net emissions of carbon dioxide for at least ten years compared to a baseline where dead trees are left standing. In most scenarios, GHG emissions reached parity with the baseline by year 20. Changes in forest carbon stocks were the biggest driver of net emission differences between salvage and no salvage scenarios. A benchmark scenario without timber harvesting or the occurrence of a spruce budworm outbreak had the greatest net carbon sequestration profile after 40 years compared to all other scenarios. Salvaging trees killed by a severe and widespread insect infestation has potential negative short-term implications for GHG emissions, but long-term resilience of these climate benefits is possible in the absence of future outbreaks or subsequent harvest activities. The results provide guidance on silvicultural interventions to minimize the impact of spruce budworm on forest carbon.

Highlights

  • Within the decade, an outbreak of eastern spruce budworm (SBW; Choristoneura fumiferana) in eastern Canada is expected to begin affecting the forest in the states of Maine, New Hampshire, Vermont, and northern New York

  • We found that forest management actions such as salvage harvesting designed to mitigate pest impacts over time can have positive impacts on overall C balances by reducing the risk of catastrophic loss in susceptible stands and landscapes and by shifting C from at-risk or dying trees to wood used as building materials or displacing fossil-fuel intensive energy sources

  • The resilience is dependent upon the recovery of the forest C stocks in the absence of subsequent natural or anthropogenic disturbances

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Summary

Introduction

An outbreak of eastern spruce budworm (SBW; Choristoneura fumiferana) in eastern Canada is expected to begin affecting the forest in the states of Maine, New Hampshire, Vermont, and northern New York (hereafter “northeastern US”). Assessing the C resilience of forests following salvage harvesting requires a comprehensive life-cycle analysis that includes changes over time in forest C stocks (including living and dead trees, and coarse woody material), harvest and manufacturing GHG emissions, wood product fate, and final disposition (e.g., Gunn and Buchholz, 2018).

Results
Conclusion

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