Implementation of wildfire- and climate-adaptation strategies in seasonally dry forests of western North America is impeded by numerous constraints and uncertainties. After more than a century of resource and land use change, some question the need for proactive management, particularly given novel social, ecological, and climatic conditions. To address this question, we first provide a framework for assessing changes in landscape conditions and fire regimes. Using this framework, we then evaluate evidence of change in contemporary conditions relative to those maintained by active fire regimes, i.e., those uninterrupted by a century or more of human-induced fire exclusion. The cumulative results of more than a century of research document a persistent and substantial fire deficit and widespread alterations to ecological structures and functions. These changes are not necessarily apparent at all spatial scales or in all dimensions of fire regimes and forest and nonforest conditions. Nonetheless, loss of the once abundant influence of low- and moderate-severity fires suggests that even the least fire-prone ecosystems may be affected by alteration of the surrounding landscape and, consequently, ecosystem functions. Vegetation spatial patterns in fire-excluded forested landscapes no longer reflect the heterogeneity maintained by interacting fires of active fire regimes. Live and dead vegetation (surface and canopy fuels) is generally more abundant and continuous than before European colonization. As a result, current conditions are more vulnerable to the direct and indirect effects of seasonal and episodic increases in drought and fire, especially under a rapidly warming climate. Long-term fire exclusion and contemporaneous social-ecological influences continue to extensively modify seasonally dry forested landscapes. Management that realigns or adapts fire-excluded conditions to seasonal and episodic increases in drought and fire can moderate ecosystem transitions as forests and human communities adapt to changing climatic and disturbance regimes. As adaptation strategies are developed, evaluated, and implemented, objective scientific evaluation of ongoing research and monitoring can aid differentiation of warranted and unwarranted uncertainties.

Evidence for widespread changes in the structure, composition, and fire regimes of western North American forests.

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.

https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1002/eap.2433

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

https://www.fs.fed.us/pnw/pubs/journals/pnw_2016_hessburg001.pdf

Tamm Review: Management of mixed-severity fire regime forests in Oregon, Washington, and Northern California

\n For over 20 years, forest fuel reduction has been the dominant management action in western US forests. These same actions have also been associated with the restoration of highly altered frequent-fire forests. Perhaps the vital element in the compatibility of these treatments is that both need to incorporate the salient characteristics that frequent fire produced—variability in vegetation structure and composition across landscapes and the inability to support large patches of high-severity fire. These characteristics can be achieved with both fire and mechanical treatments. The possible key to convergence of fuel reduction and forest restoration strategies is integrated planning that permits treatment design flexibility and a longer-term focus on fire reintroduction for maintenance. With changing climate conditions, long-term forest conservation will probably need to be focused on keeping tree density low enough (i.e., in the lower range of historic variation) for forest conditions to adapt to emerging disturbance patterns and novel ecological processes.

Forest Restoration and Fuels Reduction: Convergent or Divergent?

https://www.fs.fed.us/nrs/pubs/jrnl/2018/nrs_2018_fahey_001.pdf

Shifting conceptions of complexity in forest management and silviculture

Churchill, Derek J.; Carnwath, Gunnar C.; Larson, Andrew J.; Jeronimo, Sean A. 2017. Historical forest structure, composition, and spatial pattern in dry conifer forests of the western Blue Mountains, Oregon. Gen. Tech. Rep. PNWGTR-956. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 93 p. In frequent-fire forests of the interior Western United States, historical (prefire suppression) conditions are often used as a reference to set management objectives, guide prescriptions, and monitor treatment effectiveness. We quantified the historical size, density, composition, and spatial patterns of dry mixed-conifer forests in the Blue Mountains of Oregon to establish reference conditions that could be used for ongoing forest-restoration efforts. In total, 14 reconstruction plots ranging from 2.3 to 5.0 ha were established, with plots located on ponderosa pine (Pinus ponderosa Lawson & C. Lawson), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), and grand fir (Abies grandis (Douglas ex D. Don) Lindl.) potential vegetation sites. Within each plot, all historical structures—live trees, snags, and logs that were alive in 1890—were mapped, and 1890 diameters were reconstructed. Historical structure and composition on the 14 plots consisted of an open canopy, uneven-aged mosaic of widely spaced individual trees, tree clumps, and openings dominated by large trees. Mean values for historical tree density of trees greater than 15 cm diameter at breast height (d.b.h.) ranged from 53 to 197 trees per hectare, and basal area ranged from 11 to 24 m ∙ ha. Basal area varied widely across each plot, and the mean value was not representative of the density in the majority of the plot in almost all cases. Mean tree diameter ranged from 35.2 to 57.8 cm, with over 50 percent of the basal area composed of trees greater than 50 cm d.b.h. Species composition was dominated by ponderosa pine on plots within the ponderosa pine and Douglas-fir series. Grand fir was abundant on three of the four plots within the grand fir series, comprising 44 to 48 percent of the basal area on these three plots. The proportion of historical trees occurring as widely spaced individuals (no neighbors within 6 m) ranged from 0.53 to 0.10. Ten of 14 plots had large tree clumps (10 to 15 trees) or very large clumps (16 to 30 trees), with the proportion of trees in these clumps ranging from 0.05 to 0.43. The proportion of the plot area in large openings ranged from 0.15 to 0.72, with most openings being sinuous and linear in shape and ranging from 18 to 45 m across. The range of conditions presented in this reference dataset provides managers flexible targets that can be used to guide restoration of variable conditions within and across treatment units. When using the dataset to inform prescription development, we recommend first determining the target stem density appropriate for the site and then selecting a clumping level to help guide the spatial pattern to be created through restoration treatment. Management objectives, current conditions, biophysical conditions, and anticipated future disturbance and climate change can then be considered when setting targets for density and clumping. This reference information can also be used to monitor the extent to which treated stands are within the ranges of size, density, composition, and pattern quantified in this study.

https://www.fs.fed.us/pnw/pubs/pnw_gtr956.pdf

Historical forest structure, composition, and spatial pattern in dry conifer forests of the western Blue Mountains, Oregon

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Historical forest structure, composition, and spatial pattern in dry conifer forests of the western Blue Mountains, Oregon