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

Hagmann, R. Keala; Hessburg, Paul F.; Prichard, Susan J.; Povak, Nicholas A.; Brown, Peter M.; Fulé, Peter Z.; Keane, Robert E.; Knapp, Eric E.; Lydersen, Jamie M.; Metlen, Kerry L.; Reilly, Matthew J.; Meador, Andrew J. Sánchez; Stephens, Scott L.; Stevens, Jens T.; Taylor, Alan H.; Yocom, Larissa L.; Battaglia, Michael A.; Churchill, Derek J.; Daniels, Lori D.; Falk, Donald A.; Henson, Paul; Johnston, James D.; Krawchuk, Meg A.; Levine, Carrie R.; Meigs, Garrett W.; Merschel, Andrew G.; North, Malcolm P.; Safford, Hugh D.; Swetnam, Thomas W.; Waltz, Amy E. M.

doi:10.1002/eap.2431

Cited by 218 publications

(161 citation statements)

References 323 publications

(670 reference statements)

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“…This work did not account for some fire regime drivers, such as fuel accumulation over time due to fire suppression and land-use change [90,91], or changing patterns of ignition sources (e.g. lightning) [92].…”

Section: Limitationsmentioning

confidence: 99%

Climate-induced fire regime amplification in Alberta, Canada

Whitman

Parks

Holsinger

et al. 2022

Environ. Res. Lett.

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Acting as a top-down control on fire activity, climate strongly affects wildfire in North American ecosystems through fuel moisture and ignitions. Departures from historical fire regimes due to climate change have significant implications for the structure and composition of boreal forests, as well as fire management and operations. In this research, we characterize the relationship between trends in climate and fire regime characteristics, for a study area predominantly in Alberta, Canada. We examined trends of fire and climate in northwestern boreal forests using time series analysis of downscaled historical annual climate, fire history (1970 – 2019), and fire severity (the impacts of wildfire on plants and organic biomass; 1985 – 2018). We represented fire severity using the relativized burn ratio (RBR) calculated from multispectral Landsat imagery. The climate of the study area has significantly warmed and dried over the past 50 years. Over the same period the annual number of large wildfires, area burned, and fire sizes in the study area significantly increased. Furthermore, the likelihood, area, and number of extreme short-interval reburns (≤ 15 years between fires; 1985 – 2019) also significantly increased. During the study period, the portion of forested unburned islands within fire perimeters significantly declined, and fire severity (RBR) increased in open conifer and mixedwood forests. These fire regime changes are significantly correlated with annual climate variability, and a path analysis supports the hypothesis that annual climate patterns have led to fire regime shifts. The increasing fire activity in this region has implications for forest ecology and habitat availability, as the disruption of the fire regime is likely to alter forest recovery. Managers may face increasing challenges to fire suppression if the observed trends of increasing hotter and drier annual climate in the study area persist, driving extreme fire activity.

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Section: Limitationsmentioning

confidence: 99%

Climate-induced fire regime amplification in Alberta, Canada

Whitman

Parks

Holsinger

et al. 2022

Environ. Res. Lett.

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“…T he annual area burned by forest fires in the western United States (US) has increased ten-fold over the past halfcentury 1 , punctuated by the record 2020 western US fire season that produced widespread negative effects 2 . Several anthropogenic factors underpin growing wildland fire area, including historically high fuel loads due to a century of fire suppression and outlawing of Indigenous burning; less direct suppression tactics to support firefighter safety, and increased fuel aridity due to human-caused climate change [3][4][5][6] . While the influence of these factors varies geographically as a function of both biophysical and human-environment interactions, climate variability expressed through fuel dryness is the dominant interannual driver of macroscale burned area across fuel-rich biomes in the western US and globe 7 .…”

mentioning

confidence: 99%

Projected increases in western US forest fire despite growing fuel constraints

Abatzoglou

Battisti

Williams

et al. 2021

Commun Earth Environ

168

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Escalating burned area in western US forests punctuated by the 2020 fire season has heightened the need to explore near-term macroscale forest-fire area trajectories. As fires remove fuels for subsequent fires, feedbacks may impose constraints on the otherwise climate-driven trend of increasing forest-fire area. Here, we test how fire-fuel feedbacks moderate near-term (2021–2050) climate-driven increases in forest-fire area across the western US. Assuming constant fuels, climate–fire models project a doubling of forest-fire area compared to 1991–2020. Fire-fuel feedbacks only modestly attenuate the projected increase in forest-fire area. Even models with strong feedbacks project increasing interannual variability in forest-fire area and more than a two-fold increase in the likelihood of years exceeding the 2020 fire season. Fuel limitations from fire-fuel feedbacks are unlikely to strongly constrain the profound climate-driven broad-scale increases in forest-fire area by the mid-21st century, highlighting the need for proactive adaptation to increased western US forest-fire impacts.

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“…Hagmann et al. (2021) also review the evidence for changes in the dimensions of fire regimes (Table 1). Fire exclusion has reduced fire frequency in all forest types, with the degree of change generally declining with increasing elevation, owing to orographic effects on moisture and temperature, and topo‐edaphic effects on insolation.…”

Section: Forest Conditions and Wildfire Regimesmentioning

confidence: 99%

“…Hagmann et al. (2021) provide a comprehensive review of these papers and studies that directly evaluated them. They show that methods and inferences in these articles failed independent validation by other research groups and lend their support to the findings of the larger body of evidence.…”

Section: Forest Conditions and Wildfire Regimesmentioning

confidence: 99%

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Wildfire and climate change adaptation of western North American forests: a case for intentional management

Hessburg

Prichard

Hagmann

et al. 2021

Ecological Applications

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144

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Forest landscapes across western North America (wNA) have experienced extensive changes over the last two centuries, while climatic warming has become a global reality over the last 4 decades. Resulting interactions between historical increases in forested area and density and recent rapid warming, increasing insect mortality, and wildfire burned areas, are now leading to substantial abrupt landscape alterations. These outcomes are forcing forest planners and managers to identify strategies that can modify future outcomes that are ecologically and/or socially undesirable. Past forest management, including widespread harvest of fire-and climate-tolerant large old trees and old forests, fire exclusion (both Indigenous and lightning ignitions), and highly effective wildfire suppression have contributed to the current state of wNA forests. These practices were successful at meeting short-term demands, but they match poorly to modern realities. Hagmann et al. (in press) review a century of observations and multi-scale, multi-proxy research evidence that details widespread changes in forested landscapes and wildfire regimes since the influx of European colonists. Over the preceding 10 millennia, large areas of wNA were already settled and proactively managed with intentional burning by Indigenous tribes. Prichard et al. (in press) then review the research on management practices historically applied by Indigenous tribes and currently applied by some managers to intentionally manage forests for resilient conditions. They address ten questions surrounding the application and relevance of these management practices. Here, we highlight the main findings of both papers and offer recommendations for management. We discuss progress paralysis that often occurs with strict adherence to the precautionary principle; offer insights for dealing with the common problem of irreducible uncertainty and suggestions for reframing management and policy direction; and identify key knowledge gaps and research needs.

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

Cited by 218 publications

References 323 publications

Climate-induced fire regime amplification in Alberta, Canada

Climate-induced fire regime amplification in Alberta, Canada

Projected increases in western US forest fire despite growing fuel constraints

Wildfire and climate change adaptation of western North American forests: a case for intentional management

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