Adapting western North American forests to climate change and wildfires: 10 common questions

Abstract

We review science-based adaptation strategies for western North American (wNA) forests that include restoring active fire regimes and fostering resilient structure and composition of forested landscapes. As part of the review, we address common questions associated with climate adaptation and realignment treatments that run counter to a broad consensus in the literature. These include the following: (1) Are the effects of fire exclusion overstated? If so, are treatments unwarranted and even counterproductive? (2) Is forest thinning alone sufficient to mitigate wildfire hazard? (3) Can forest thinning and prescribed burning solve the problem? (4) Should active forest management, including forest thinning, be concentrated in the wildland urban interface (WUI)? (5) Can wildfires on their own do the work of fuel treatments? (6) Is the primary objective of fuel reduction treatments to assist in future firefighting response and containment? (7) Do fuel treatments work under extreme fire weather? (8) Is the scale of the problem too great? Can we ever catch up? (9) Will planting more trees mitigate climate change in wNA forests? And (10) is post-fire management needed or even ecologically justified? Based on our review of the scientific evidence, a range of proactive management actions are justified and necessary to keep pace with changing climatic and wildfire regimes and declining forest heterogeneity after severe wildfires. Science-based adaptation options include the use of managed wildfire, prescribed burning, and coupled mechanical thinning and prescribed burning as is consistent with land management allocations and forest conditions. Although some current models of fire management in wNA are averse to short-term risks and uncertainties, the long-term environmental, social, and cultural consequences of wildfire management primarily grounded in fire suppression are well documented, highlighting an urgency to invest in intentional forest management and restoration of active fire regimes.

Keywords: Climate Change and Western Wildfires; adaptive management; carbon; climate change; cultural burning; ecological resilience; forest management; fuel treatments; managed wildfire; mechanical thinning; prescribed fire; restoration; wildland fire.

Fig. 1

(A) Dry mixed‐conifer forests. Theorized responses of seasonally dry mixed‐conifer forest biomass to wildfire and three fire management scenarios under 21st‐century climate change. (a) Partial wildfire suppression with only a small fraction of forested landscape treated each year (˜1%). In this scenario, escaped high‐severity wildfires are the dominant change agent with a high probability of forest conversion to nonforest as represented in the ball and cup figure by a shallow forest basin of attraction and a deep and broad nonforest basin of attraction. (b) A large percentage of the forested landscape (>50%) is treated either by frequent low and moderate severity fires or fuel reduction treatments with ongoing maintenance. Large wildfires are infrequent, and fire severity within the event perimeter is mostly low and moderate severity as represented in the ball and cup figure by a deep and wide forest basin of attraction and a moderately deep and wide nonforest basin of attraction. (c) Aggressive wildfire suppression with no active fuel reduction treatments; similar to scenario A but with even a higher likelihood of forest to nonforest conversion. (B) Cold forests. Wildfire management scenarios represent two levels of wildland fire management under 21st‐century climate change. (d) Cold forest area treated with moderately frequent fires of moderate and high severity. Because large fire events are relatively rare, forest regeneration is supported by patchworks of remnant forest, represented by a deep and wide forest basin of attraction. (e) Aggressive fire suppression with no active fuel treatments. In this scenario, escaped wildfires are the major change agent through large, mostly high severity fires. Forest regeneration is limited by large, high severity fire events, and conversion to nonforest is common; represented by a shallow and narrow forest basin of attraction and a deep and broad nonforest basin of attraction.

Fig. 2

Representative photos of (A) fuel reduction treatment (maintenance surface fire in a previously thinned and burned forest); (B) fuel rearrangement (forest residues following mechanical thinning); and (C) fuel accumulation (fire excluded forest with grand fir infilling around western larch trees). Photo credits: Roger Ottmar, Susan Prichard, and John Marshall.

Fig. 3

Active forest restoration treatment, Sinlahekin Wildlife Refuge, Washington Department of Fish and Wildlife. Top left: multi‐layered, dense dry mixed conifer forest after 100 yr of fire exclusion. Top right: residual forest after a variable density thinning treatment. Bottom right: treated condition after pile and broadcast burning. Bottom left: post‐wildfire photo after the 2015 Lime Belt fire. Photo credit: John Marshall.

Fig. 4

Conceptual diagram of low and moderate severity fire effects on post‐fire residual structure. Top: frequent fire reduces surface and ladder fuels. Middle: gradual accumulation of live and dead fuels between fires. Bottom: conditions after prolonged fire exclusion. Forest is denser and more layered, and high‐severity fire is likely. Drawing credit: Robert Van Pelt.