Setting the Stage for Mixed- and High-Severity Fire

Hanson, Chad T.; Sherriff, Rosemary L.; Hutto, Richard L.; DellaSala, Dominick A.; Veblen, Thomas T.; Baker, William L.

doi:10.1016/b978-0-12-802749-3.00001-3

Cited by 7 publications

(7 citation statements)

References 110 publications

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“…, Hanson et al. ). Historical forests were often younger, denser, and had been burned in fires varying in intensity and severity, as described explicitly in Hessburg et al.…”

Section: Historical Variability In Natural Disturbance and Recovery Imentioning

confidence: 99%

Transitioning western U.S. dry forests to limited committed warming with bet‐hedging and natural disturbances

Baker

2018

Ecosphere

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Historical evidence suggests natural disturbances could allow more forest persistence, than expected from models, over 40 yr of transition to the net‐zero emissions needed to limit warming to <2.0°C (e.g., Paris Agreement). Forests must ultimately equilibrate with committed warming from accumulated emissions. Historical dry‐forest landscapes were heterogeneous from large, infrequent disturbances (LIDs) that reduced tree density and basal area, followed by slow, variable tree regeneration and recovery for 1–3 centuries. These together effectively provided bet‐hedging through stand‐ and landscape‐level heterogeneity that enhanced resistance and resilience to a diversity of unpredictable subsequent disturbances. Recent disturbances have not yet exceeded historical variability in rates and patterns, but could cause mortality of ∼26–51% of dry‐forest area in the transition. This also means 1/2 to 3/4 of dry‐forest area could escape most mortality and the mortality area could also have substantial forest persistence. Projections are unavailable for droughts or beetle outbreaks, but they recently caused about 3–4 times as much tree mortality as did moderate‐ to high‐severity fires. Mortality could reduce forest area if new trees do not regenerate, but 24 studies showed recent regeneration after high‐severity fires was slow, but indistinct from historical variability. Survival of smaller trees provided regeneration after beetle outbreaks and droughts. Regeneration in general was projected by 2060 to decline by ∼10% in one study and increase by 50% in another. If openings from disturbances increased, some grasslands and shrublands could be restored, increasing landscape heterogeneity and resistance to disturbance spread. Given these trends and our limited ability to prevent LIDs, I suggest (1) refocusing restoration to increase bet‐hedging resilience to droughts and beetle outbreaks by retaining small trees and diverse tree species, (2) expanding development of fire‐safe landscapes to protect people and infrastructure from unavoidable increased fire, (3) enabling more managed fire to restore and enhance stand‐ and landscape‐scale bet‐hedging, and (4) accepting that LIDs will revise resistance, resilience, and adaptation, which enhance forest persistence, particularly if post‐disturbance survivors are not logged and trees are not planted. Natural disturbance and slow recovery, if bet‐hedged to increase resistance and resilience, could enable substantial forest persistence.

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“…, Hanson et al. ). Historical forests were often younger, denser, and had been burned in fires varying in intensity and severity, as described explicitly in Hessburg et al.…”

Section: Historical Variability In Natural Disturbance and Recovery Imentioning

confidence: 99%

Transitioning western U.S. dry forests to limited committed warming with bet‐hedging and natural disturbances

Baker

2018

Ecosphere

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“…, Hanson et al. ). At the other end of the fire regime spectrum, cooler, moister forest types, such as lodgepole pine forests, support fire regimes dominated by severe fire events (Brown and Smith ), although mixed‐ and low‐severity fires are known to occur in these types as well (Barrett et al.…”

Section: Fire History Studies Suggest That Severe Fire Is An Integralmentioning

confidence: 99%

Toward a more ecologically informed view of severe forest fires

et al. 2016

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Abstract.We use the historical presence of high-severity fire patches in mixed-conifer forests of the western United States to make several points that we hope will encourage development of a more ecologically informed view of severe wildland fire effects. First, many plant and animal species use, and have sometimes evolved to depend on, severely burned forest conditions for their persistence. Second, evidence from fire history studies also suggests that a complex mosaic of severely burned conifer patches was common historically in the West. Third, to maintain ecological integrity in forests born of mixed-severity fire, land managers will have to accept some severe fire and maintain the integrity of its aftermath. Lastly, public education messages surrounding fire could be modified so that people better understand and support management designed to maintain ecologically appropriate sizes and distributions of severe fire and the complex early-seral forest conditions it creates.

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“…The size and configuration of refugia within burn perimeters may provide a range of habitat, seed sources, and support for ecological processes that collectively contribute to post-fire resilience often overlooked after large and/or uncharacteristically severe fire events [6,8,9,[11][12][13]. While areas of stand-replacing fire can enhance biodiversity in some systems by giving rise to early seral communities and providing habitat important to a wide variety of biota [51] fire refugia represent habitat islands for forest-dependent species within a highly disturbed matrix. Ecologically optimal patch sizes and distributions are likely dependent on system-, process-, or species-specific dynamics [52,53].…”

Section: Refugia Patch Size and Spatial Distributionmentioning

confidence: 99%

How Much Forest Persists Through Fire? High-Resolution Mapping of Tree Cover to Characterize the Abundance and Spatial Pattern of Fire Refugia Across Mosaics of Burn Severity

Walker

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Downing

et al. 2019

Forests

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Wildfires in forest ecosystems produce landscape mosaics that include relatively unaffected areas, termed fire refugia. These patches of persistent forest cover can support fire-sensitive species and the biotic legacies important for post-fire forest recovery, yet little is known about their abundance and distribution within fire perimeters. Readily accessible 30-m resolution satellite imagery and derived burn severity products are commonly employed to characterize post-fire landscapes; however, coarse image resolution, generalized burn severity thresholds, and other limitations can constrain accurate representation of fire refugia. This study quantifies the abundance and pattern of fire refugia within 10 fires occurring in ponderosa pine and dry mixed-conifer forests between 2000 and 2003. We developed high-resolution maps of post-fire landscapes using semi-automated, object-based classification of 1-m aerial imagery, conducted imagery- and field-based accuracy assessments, and contrasted these with Landsat-derived burn severity metrics. Fire refugia area within burn perimeters ranged from 20% to 57%. Refugia proportion generally decreased with increasing Landsat-derived burn severity, but still accounted for 3–12% of areas classified as high severity. Patch size ranged from 1-m2 isolated trees to nearly 8000 ha, and median patch size was 0.01 ha—substantially smaller than a 30-m Landsat pixel. Patch size was negatively related to burn severity; distance to fire refugia from open areas was positively related to burn severity. Finally, optimized thresholds of 30-m post-fire normalized burn ratio (NBR) and relative differenced normalized burn ratio (RdNBR) delineated fire refugia with an accuracy of 77% when validated against the 1-m resolution maps. Estimations of fire refugia abundance based on Landsat-derived burn severity metrics are unlikely to detect small, isolated fire refugia patches. Finer-resolution maps can improve understanding of the distribution of forest legacies and inform post-fire management activities including reforestation and treatments.

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Setting the Stage for Mixed- and High-Severity Fire

Cited by 7 publications

References 110 publications

Transitioning western U.S. dry forests to limited committed warming with bet‐hedging and natural disturbances

Transitioning western U.S. dry forests to limited committed warming with bet‐hedging and natural disturbances

Toward a more ecologically informed view of severe forest fires

How Much Forest Persists Through Fire? High-Resolution Mapping of Tree Cover to Characterize the Abundance and Spatial Pattern of Fire Refugia Across Mosaics of Burn Severity

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