Are Wildland Fires Increasing Large Patches of Complex Early Seral Forest Habitat?

DellaSala, Dominick A.; Hanson, Chad T.

doi:10.3390/d11090157

Cited by 19 publications

(12 citation statements)

References 72 publications

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“…Different management actions are associated with these two schools of thought. If the fire regime is not altered, management actions are unnecessary or may have unintended negative consequences on forest productivity or critical habitat (Odion et al, 2014;Baker, 2015;DellaSala and Hanson, 2019). Where fire regimes have been altered, determining the causes and degree of departure is important for taking appropriate management actions (Fulé et al, 1997;Stephens et al, 2013;Hessburg et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

A Disrupted Historical Fire Regime in Central British Columbia

et al. 2021

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In the 2017 and 2018, 2.55 million hectares burned across British Columbia, Canada, including unanticipated large and high-severity fires in many dry forests. To transform forest and fire management to achieve resilience to future megafires requires improved understanding historical fire frequency, severity, and spatial patterns. Our dendroecological reconstructions of 35 plots in a 161-hectare study area in a dry Douglas-fir forest revealed historical fires that burned at a wide range of frequencies and severities at both the plot- and study-area scales. The 23 fires between 1619 and 1943 burned at intervals of 10–30 years, primarily at low- to moderate-severity that scarred trees but generated few cohorts. In contrast, current fire-free intervals of 70–180 years exceed historical maximum intervals. Of the six widespread fires from 1790 to 1905, the 1863 fire affected 86% of plots and was moderate in severity with patches of higher severity that generated cohorts at fine scales only. These results indicate the severity of fires varied at fine spatial scales, and offer little support for the common assertion that periodic, high-severity, stand-initiating events were a component of the mixed-severity fire regime in these forest types. Many studies consider fires in the late 1800s relatively severe because they generated new cohorts of trees, and thus, emphasize the importance of high-severity fires in a mixed-severity fire regime. In our study area, the most widespread and severe fire was not a stand-initiating fire. Rather, the post-1863 cohorts persisted due disruption of the fire regime in the twentieth century when land-use shifted from Indigenous fire stewardship and early European settler fires to fire exclusion and suppression. In absence of low- to moderate-severity fires, contemporary forests are dense with closed canopies that are vulnerable to high-severity fire. Future management should reduce forest densities and to restore stand- and landscape-level heterogeneity and increase forest resilience. The timing and size of repeat treatments such as thinning of subcanopy trees and prescribed burning, including Indigenous fire stewardship, can be guided by our refined understanding of the mixed-severity fire regime that was historically dominated by low- to moderate-severity fires in this dry forest ecosystem.

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Section: Introductionmentioning

confidence: 99%

A Disrupted Historical Fire Regime in Central British Columbia

et al. 2021

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“…In recent years, some burned areas have exceeded 4.05 Mha (Murphy et al., 2018 ), despite suppression attempts (Coop et al., 2020 ; North et al., 2019 ). Because large fires can produce a distribution of patch sizes burned at different severity (Dellasala & Hanson, 2019 ; Turner et al., 1994 ), it is important to understand how distances to refuge are affected by fire and landscape properties and the minimum size of patches that function effectively as wildlife refuge.…”

Section: Shifts In Dominant Vegetation Associated With Changing Wildfire Regimesmentioning

confidence: 99%

“…Late‐successional (“old‐growth”) forests are increasingly rare, yet they support threatened or endangered species with specialized habitat requirements (Dellasala & Hanson, 2019 ; Jones et al., 2016 ; Wan et al., 2019 ). Fortunately, these forests, with cooling from multilayer canopies and larger, hardier trees, tend to burn at lower severity (Lesmeister et al., 2019 ), and permitting fires in less‐vulnerable habitats or under cool, wet conditions has been suggested (Reilly et al., 2017 ).…”

Section: Climate Adaptation Planning For Forests Of Western North Americamentioning

confidence: 99%

Resilience of terrestrial and aquatic fauna to historical and future wildfire regimes in western North America

Jager

Long

Malison

et al. 2021

Ecology and Evolution

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Wildfires in many western North American forests are becoming more frequent, larger, and severe, with changed seasonal patterns. In response, coniferous forest ecosystems will transition toward dominance by fire‐adapted hardwoods, shrubs, meadows, and grasslands, which may benefit some faunal communities, but not others. We describe factors that limit and promote faunal resilience to shifting wildfire regimes for terrestrial and aquatic ecosystems. We highlight the potential value of interspersed nonforest patches to terrestrial wildlife. Similarly, we review watershed thresholds and factors that control the resilience of aquatic ecosystems to wildfire, mediated by thermal changes and chemical, debris, and sediment loadings. We present a 2‐dimensional life history framework to describe temporal and spatial life history traits that species use to resist wildfire effects or to recover after wildfire disturbance at a metapopulation scale. The role of fire refuge is explored for metapopulations of species. In aquatic systems, recovery of assemblages postfire may be faster for smaller fires where unburned tributary basins or instream structures provide refuge from debris and sediment flows. We envision that more‐frequent, lower‐severity fires will favor opportunistic species and that less‐frequent high‐severity fires will favor better competitors. Along the spatial dimension, we hypothesize that fire regimes that are predictable and generate burned patches in close proximity to refuge will favor species that move to refuges and later recolonize, whereas fire regimes that tend to generate less‐severely burned patches may favor species that shelter in place. Looking beyond the trees to forest fauna, we consider mitigation options to enhance resilience and buy time for species facing a no‐analog future.

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“…In ponderosa pine (Pinus ponderosa) and mixed-conifer forests inhabited by California spotted owls (Strix occidentalis occidentalis) in the Sierra Nevada mountains, historical fire regimes were characterized by a mix of fire severities, comprised primarily of low/moderate-severity effects but also including substantial occurrence of high-severity fire (Mallek et al, 2013;Baker, 2014;Odion et al, 2014;Doerr and Santín, 2016;Baker and Hanson, 2017), in which most or all live trees become snags (Miller and Thode, 2007). However, while it is clear from numerous lines of evidence that large high-severity fire patches (hundreds of ha in size and larger) occurred historically in relatively frequent-fire forest types like ponderosa pine and mixed-conifer in the Sierra Nevada (Leiberg, 1902;Baker, 2014;DellaSala and Hanson, 2019), debate remains about the historical frequency of occurrence of large patches of high-severity fire in these forests and concern exists about the response of forest ecosystems to some large fires that have occurred in recent years (Stephens et al, 2013;Hessburg et al, 2016;Stevens et al, 2016). Similar issues and concerns have been expressed globally, in forests and other ecosystems.…”

Section: Introductionmentioning

confidence: 99%

Impacts of Postfire Management Are Unjustified in Spotted Owl Habitat

Hanson

Tonja²

2021

Front. Ecol. Evol.

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In mixed-conifer forests inhabited by California spotted owls, land managers hypothesize that without human intervention natural conifer regeneration will take many decades or longer to begin within interior areas of large high-severity fire patches, due to long distances from live tree seed sources. As a result, widespread post-fire logging, followed by sprayed application of herbicides and planting of conifer seedlings, are used to create tree plantations. These are activities routinely conducted in spotted owl territories following fires, despite current data that indicate this approach has adverse impacts on spotted owl occupancy. Land managers acknowledge such impacts, but continue these forest management practices, assuming they are a necessary harm, one that is warranted to ensure the later return of mature conifer forests used by spotted owls for nesting and roosting. However, few data have been gathered to test this hypothesis. At 5 years post-fire, we surveyed field plots on a grid within large high-severity fire patches in spotted owl habitat within the Rim fire of 2013 in the Sierra Nevada, California. In our analysis the percentage of plots lacking conifer regeneration decreased significantly with larger plot sizes, a finding contrary to previous studies which assumed vast “deforested” areas in wildland fires, a bias created by small plot size. We found higher conifer regeneration closer to live-tree edges, but we consistently found natural post-fire conifer regeneration at all distances into interior spaces of large high-severity fire patches, including >300 m from the nearest live trees. Distance from live-tree edges did not affect pine dominance in post-fire regeneration. The post-fire natural conifer regeneration reported in our results suggests that the adverse effects of current post-fire management in spotted owl habitat are not necessary practices that can be justified.

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Are Wildland Fires Increasing Large Patches of Complex Early Seral Forest Habitat?

Cited by 19 publications

References 72 publications

A Disrupted Historical Fire Regime in Central British Columbia

A Disrupted Historical Fire Regime in Central British Columbia

Resilience of terrestrial and aquatic fauna to historical and future wildfire regimes in western North America

Impacts of Postfire Management Are Unjustified in Spotted Owl Habitat

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