Pyrosilviculture Needed for Landscape Resilience of Dry Western United States Forests

Abstract

A significant increase in treatment pace and scale is needed to restore dry western US forest resilience owing to increasingly frequent and severe wildfire and drought. We propose a pyrosilviculture approach to directly increase large-scale fire use and modify current thinning treatments to optimize future fire incorporation. Recommendations include leveraging wildfire’s “treatment” in areas burned at low and moderate severity with subsequent pyrosilviculture management, identifying managed wildfire zones, and facilitating and financing prescribed fire with “anchor,” “ecosystem asset,” and “revenue” focused thinning treatments. Pyrosilviculture would also expand prescribed-burn and managed-wildfire objectives to include reducing stand density, increasing forest heterogeneity, and selecting for tree species and phenotypes better adapted to changing climate and disturbance regimes. The potential benefits and limitations of this approach are discussed. Fire is inevitable in dry western US forests and pyrosilviculture focuses on proactively shifting more of that fire into managed large-scale burns needed to restore ecosystem resilience. Study Implications A management paradigm shift in fire use is needed to restore western forest landscape resilience. We propose a “pyrosilviculture” approach with the goals of directly increasing prescribed fire and managed wildfire and modifying thinning treatments to optimize more managed fire. Changes include leveraging low- and moderate-wildfire burn areas as treatments, identifying managed wildfire zones, and three thinning treatments designed to expand and finance prescribed fire to connect dispersed treatments. We also suggest that large-scale fire be used to reduce forest density, increase structural heterogeneity, and select for tree species and phenotypes adapted to changing climate and fire conditions.

Severity patterns of the 2021 Dixie Fire exemplify the need to increase low-severity fire treatments in California’s forests

“…Integration of fire and forest management and expanded use of prescribed and managed fire are necessary conditions for success. Current treatment rates are an order of magnitude lower than historical rates of fuel reduction from pre-fire exclusion fire regimes [13,19]. Moreover, annual area burned by wildfires is ca.…”

“…Mechanical fuel treatments alone, without burning, showed only limited ability to dampen the severity of the Dixie fire, and only if the treatment had occurred within the past 10 years. This limited influence of mechanical treatments on wildfire severity is noteworthy and is likely related to the generally small and dispersed nature of treatments [13], the extreme climate and weather conditions that drove spread and severity of the Dixie Fire, and inconsistent follow up with prescribed fire after mechanical treatment to consume surface fuels and makes treatments more effective. Mechanical treatments followed by prescribed fire have been observed to reduce fire severity in other large California wildfires [13].…”

“…This limited influence of mechanical treatments on wildfire severity is noteworthy and is likely related to the generally small and dispersed nature of treatments [13], the extreme climate and weather conditions that drove spread and severity of the Dixie Fire, and inconsistent follow up with prescribed fire after mechanical treatment to consume surface fuels and makes treatments more effective. Mechanical treatments followed by prescribed fire have been observed to reduce fire severity in other large California wildfires [13]. Areas previously burned at high-severity within the Dixie Fire also played forward and tended to reburn at high severity again.…”

Prescribed fire selects for a pyrophilous soil subcommunity in a northern California mixed conifer forest

“…A key strategy toward decreasing the frequency of devastating wildfires is the implementation of lower-intensity prescribed fires and managed wildfires. These lower-intensity controlled burns have proven effective in reducing the fuel load and the likelihood of catastrophic fire [8][9][10]. While the effects of prescribed fire on plant and animal communities are increasingly well-documented [9][10][11][12][13], our understanding of the impact of fire management strategies on microbial communities is much more limited [14].…”

“…These lower-intensity controlled burns have proven effective in reducing the fuel load and the likelihood of catastrophic fire [8][9][10]. While the effects of prescribed fire on plant and animal communities are increasingly well-documented [9][10][11][12][13], our understanding of the impact of fire management strategies on microbial communities is much more limited [14]. In this study, we investigated the effects of prescribed burns on soil bacteria and fungi with the aim of understanding the ecological processes that shape these communities.…”