Climate risks to carbon sequestration in US forests

Abstract

Forests are currently a substantial carbon sink globally. Many climate change mitigation strategies rely on forest preservation and expansion, but the effectiveness of these approaches hinges on forests sequestering carbon for centuries despite anthropogenic climate change. Yet climate-driven disturbances pose critical risks to the long-term stability of forest carbon. We quantify the key climate drivers that fuel wildfire, drought, and insects, for the United States over 1984-2018 and project future disturbance risks over the 21st century. We find that current risks are widespread and projected to increase across different emission scenarios by a factor of 4-14 for fire and 1.3-1.8 for drought and insects. Our results provide insights for carbon cycle modeling, conservation, and climate policy, underscoring the escalating climate risks facing forests and the need for emissions reductions to mitigate climate change.

Informing Nature‐based Climate Solutions for the United States with the best‐available science

“…In the meantime, policy mechanisms could be developed that specifically favor the implementation of NbCS in places where biophysical impacts are likely to be favorable, and where the threat of impermanence is comparatively low. For example, in the mesic and highly productive Eastern US, the risks of wildfire, drought, and insect‐driven tree mortality are relatively small (Anderegg et al, 2021), and enhancing plant cover in the Eastern part of the country tends to have a surface cooling effect (Kaye & Quemada, 2017; Zhang et al, 2020). Thus, NbCS projects in the Eastern US that enhance tree cover may be a “safer bet” when compared to projects in the drought‐ and fire‐prone Western US or Alaska.…”

The complexity of biological disturbance agents, fuels heterogeneity, and fire in coniferous forests of the western United States

“…Future risks of drought- and insect-related tree mortality are also projected to increase substantially during the 21st century in California and the southwest but decrease in the PNW based on climate model projections using historical data records from forest inventories ( Anderegg et al, 2021 ). An emerging theme of the influence of climate change on BDAs is the “rise of the secondaries”, i.e., the pathogens and insects previously considered unimportant in tree mortality may become increasingly important as climate changes and tree stress increases ( Cohen et al, 2016 ; Hennon et al, 2020 ).…”

“…From an ecosystem perspective, a healthy forest should be able to resist (“resistance”) or to recover (“resilience”) from biological disturbance ( Merschel et al, 2021 ). The ability to be resistant or resilient is affected by a complex interaction of factors in western USA coniferous forests including: fire suppression, fuel characteristics, tree density, drought and shade tolerance, forest management effects on forest composition and structure (historic logging of large trees that were resistant to drought, fire, and BDAs), changing climate (longer hotter growing seasons combined with hotter drought, uncharacteristic fires and fire weather), as well as BDA activity ( Halofsky et al, 2020 ; Anderegg et al, 2021 ; Merschel et al, 2021 ).…”