Vegetation and topographical correlates of fire severity from two fires in the Klamath-Siskiyou region of Oregon and California

We used vegetation data collected in areas before they were burned by the 2500 ha Quartz fire in southern Oregon and the 50 600 ha Big Bar complex in northern California to evaluate the ability of vegetation and topographic characteristics to predict patterns of fire severity. Fire severity was characterized as high, moderate, or low based on crown scorch and consumption, and changes in soil structure. In both fires, vegetation plots with southern aspects were more likely to burn with high severity than plots with eastern, northern, or western aspects. This was the only consistent predictor across both fires. In the Quartz fire, we found that plots at higher elevations and with larger diameter trees were more likely to burn with low or moderate severity. These correlations may have been influenced in part by the effects of unmeasured weather conditions. We found few strong correlates in the Big Bar complex, owing in part to the fact that most (75%) of our plots were in the low-severity category, providing relatively little variation. These results, in combination with previous studies of fire severity in the Klamath-Siskiyou region, suggest that areas with southern aspects tend to burn with greater severity than those of other aspects, areas with large trees burn less severely than those with smaller trees, and that correlates of fire severity vary extensively among fires.

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Post-fire survival and flushing in three Sierra Nevada conifers with high initial crown scorch

International Journal of Wildland Fire ◽

10.1071/wf08129 ◽

2009 ◽

Vol 18 (7) ◽

pp. 857 ◽

Cited By ~ 8

Author(s):

Chad T. Hanson ◽

Malcolm P. North

Keyword(s):

Sierra Nevada ◽

Pinus Ponderosa ◽

Fire Severity ◽

Conifer Species ◽

Mature Trees ◽

Salvage Logging ◽

Abies Magnifica ◽

Crown Scorch ◽

Tree Survival ◽

Large Trees

With growing debate over the impacts of post-fire salvage logging in conifer forests of the western USA, managers need accurate assessments of tree survival when significant proportions of the crown have been scorched. The accuracy of fire severity measurements will be affected if trees that initially appear to be fire-killed prove to be viable after longer observation. Our goal was to quantify the extent to which three common Sierra Nevada conifer species may ‘flush’ (produce new foliage in the year following a fire from scorched portions of the crown) and survive after fire, and to identify tree or burn characteristics associated with survival. We found that, among ponderosa pines (Pinus ponderosa Dougl. ex. Laws) and Jeffrey pines (Pinus jeffreyi Grev. & Balf) with 100% initial crown scorch (no green foliage following the fire), the majority of mature trees flushed, and survived. Red fir (Abies magnifica A. Murr.) with high crown scorch (mean = 90%) also flushed, and most large trees survived. Our results indicate that, if flushing is not taken into account, fire severity assessments will tend to overestimate mortality and post-fire salvage could remove many large trees that appear dead but are not.

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Older forests used by northern spotted owls functioned as fire refugia during large wildfires, 1987–2017

10.21203/rs.3.rs-280175/v1 ◽

2021 ◽

Author(s):

Damon B Lesmeister ◽

Raymond J. Davis ◽

Stan G. Sovern ◽

Zhiqiang Yang

Keyword(s):

Fire Regime ◽

Fire Severity ◽

Weather Conditions ◽

Fire Regimes ◽

Bimodal Distribution ◽

Relative Difference ◽

Positive Trend ◽

Forest Types ◽

Spotted Owl ◽

High Severity

Abstract Background The northern spotted owl (Strix occidentalis caurina) is an Endangered Species Act-listed subspecies that requires forests with old-growth characteristics for nesting. With climate change, large, severe wildfires are expected to be more common and an increasing threat to spotted owl persistence. Understanding fire severity patterns related to nesting forest can be valuable for forest management that supports conservation and recovery, especially if nesting forest functions as fire refugia (i.e., lower fire severity than surrounding landscape). We examined the relationship between fire severity and nesting forests in 472 large wildfires (> 200 ha) that occurred rangewide during 1987–2017. We mapped fire severities (unburned-low, moderate, high) within each fire using relative difference normalized burn ratios and quantified differences in severity between pre-fire nesting forest (edge and interior) and non-nesting forest. We also quantified these relationships within areas of three fire regimes (low severity, very frequent; mixed severity, frequent; high severity, infrequent). Results Averaged over all fires, the interior nesting forest burned at lower severity than edge or non-nesting forest. These relationships were consistent within the low severity, very frequent and mixed severity, frequent fire regime areas. All forest types burned at similar severity within the high severity, infrequent fire regime. During two of the most active wildfire years that also had the largest wildfires occurring in rare and extreme weather conditions, we found a bimodal distribution of fire severity in all forest types. In those years, a higher amount—and proportion—of all forest types burned at high severity. Over the duration of the study, we found a strong positive trend in the proportion of wildfires that burned at high severity in the non-nesting forests, but not in the two nesting forest types. Conclusions Under most wildfire conditions, the microclimate of interior patches of nesting forests likely mitigated fire severity and thus functioned as fire refugia. With changing climates, the future of interior forest as fire refugia is unknown, but trends suggest these older forests can dampen the effect of increased wildfire activity and thus an important component of landscape plans focused on fire resiliency.

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The influence of ignition technique on fire behaviour in spinifex open woodland in semiarid northern Australia

International Journal of Wildland Fire ◽

10.1071/wf14177 ◽

2015 ◽

Vol 24 (5) ◽

pp. 607 ◽

Cited By ~ 5

Author(s):

Paul R. Williams ◽

Eleanor M. Collins ◽

Mick Blackman ◽

Clare Blackman ◽

Jackie McLeod ◽

...

Keyword(s):

Fire Severity ◽

Weather Conditions ◽

Fire Season ◽

Northern Australia ◽

Fire Behaviour ◽

Factors Influencing ◽

Crown Scorch ◽

The World ◽

Open Woodland ◽

Season Of Burning

Unplanned, unmanaged wildfires are a significant threat to people, infrastructure and ecosystems around the world. Managed, planned burning is widely used for reducing the incidence, extent or intensity of wildfires. Fire weather and the season of burning are recognised as crucial factors influencing fire behaviour but the demonstrated influence of ignition technique on fire behaviour is not as prominently discussed in relation to planned fires. We found wildfires, irrespective of season, burnt the ground layer more completely (i.e. were less patchy) and produced greater crown scorch severity than did planned fires in a spinifex (Triodia spp.)-dominated open woodland. Fires ignited with a 50-m line burning with the wind produced significantly higher intensities than did line ignition against the wind, and spot ignitions with or against the wind. These data suggest that the higher severity of wildfires in spinifex-dominated habitats is strongly influenced by long fire fronts, in addition to fire season and weather conditions. This study supports the value of planned burning for reducing fire severity and highlights the value of spot ignitions in ecological burning to create a patchily burnt landscape, with limited canopy severity.

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Northern spotted owl nesting forests as fire refugia: a 30-year synthesis of large wildfires

Fire Ecology ◽

10.1186/s42408-021-00118-z ◽

2021 ◽

Vol 17 (1) ◽

Author(s):

Damon B. Lesmeister ◽

Raymond J. Davis ◽

Stan G. Sovern ◽

Zhiqiang Yang

Keyword(s):

Fire Regime ◽

Fire Severity ◽

Weather Conditions ◽

Fire Regimes ◽

Positive Trend ◽

Forest Types ◽

Spotted Owl ◽

High Severity ◽

Northern Spotted Owl ◽

Lower Severity

Abstract Background The northern spotted owl (Strix occidentalis caurina) is an Endangered Species Act-listed subspecies that requires coniferous forests with structurally complex and closed-canopy old-growth characteristics for nesting. With climate change, large wildfires are expected to become more common within the subspecies’ range and an increasing threat to these types of forests. Understanding fire severity patterns related to suitable nesting forest will be important to inform forest management that affects conservation and recovery. We examined the relationship between fire severity and suitable nesting forest in 472 large wildfires (> 200 ha) that occurred in the northern spotted owl range during 1987–2017. We mapped fire severities (unburned-low, moderate, high) within each fire using relative differenced normalized burn ratios and quantified differences in severity between pre-fire suitable nesting forest (edge and interior) and non-nesting forest. We also quantified these relationships within areas of three fire regimes (low severity, very frequent; mixed severity, frequent; high severity, infrequent). Results Averaged over all fires, the interior nesting forest burned at lower severity than edge or non-nesting forest. These relationships were consistent within the low severity, very frequent, and mixed severity, frequent fire regime areas. All forest types burned at similar severity within the high severity, infrequent fire regime. During two of the most active wildfire years that also had the largest wildfires occurring in rare and extreme weather conditions, we found a bimodal distribution of fire severity in all forest types. In those years, a higher amount—and proportion—of all forest types burned at high severity. Over the 30-year study, we found a strong positive trend in the proportion of wildfires that burned at high severity in the non-nesting forests, but not in the suitable nesting forest types. Conclusions Under most wildfire conditions, the microclimate of interior patches of suitable nesting forests likely mitigated fire severity and thus functioned as fire refugia (i.e., burning at lower severity than the surrounding landscape). With changing climate, the future of interior forest as fire refugia is unknown, but trends suggest older forests can dampen the effect of increased wildfire activity and be an important component of landscapes with fire resiliency.

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Fire and Mechanical Forest Management Treatments Support Different Portions of the Bird Community in Fire-Suppressed Forests

Forests ◽

10.3390/f12020150 ◽

2021 ◽

Vol 12 (2) ◽

pp. 150

Author(s):

Lance Jay Roberts ◽

Ryan Burnett ◽

Alissa Fogg

Keyword(s):

Sierra Nevada ◽

Fire Severity ◽

Bird Species ◽

Bird Community ◽

Fire Disturbance ◽

Long Term Effects ◽

High Severity ◽

Commercial Thinning ◽

Silvicultural Management ◽

Total Community

Silvicultural treatments, fire, and insect outbreaks are the primary disturbance events currently affecting forests in the Sierra Nevada Mountains of California, a region where plants and wildlife are highly adapted to a frequent-fire disturbance regime that has been suppressed for decades. Although the effects of both fire and silviculture on wildlife have been studied by many, there are few studies that directly compare their long-term effects on wildlife communities. We conducted avian point counts from 2010 to 2019 at 1987 in situ field survey locations across eight national forests and collected fire and silvicultural treatment data from 1987 to 2016, resulting in a 20-year post-disturbance chronosequence. We evaluated two categories of fire severity in comparison to silvicultural management (largely pre-commercial and commercial thinning treatments) as well as undisturbed locations to model their influences on abundances of 71 breeding bird species. More species (48% of the community) reached peak abundance at moderate-high-severity-fire locations than at low-severity fire (8%), silvicultural management (16%), or undisturbed (13%) locations. Total community abundance was highest in undisturbed dense forests as well as in the first few years after silvicultural management and lowest in the first few years after moderate-high-severity fire, then abundance in all types of disturbed habitats was similar by 10 years after disturbance. Even though the total community abundance was relatively low in moderate-high-severity-fire habitats, species diversity was the highest. Moderate-high-severity fire supported a unique portion of the avian community, while low-severity fire and silvicultural management were relatively similar. We conclude that a significant portion of the bird community in the Sierra Nevada region is dependent on moderate-high-severity fire and thus recommend that a prescribed and managed wildfire program that incorporates a variety of fire effects will best maintain biodiversity in this region.

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Influence of wildfire severity on geomorphic features and riparian vegetation of forested streams of the Sierra Nevada, California, USA

International Journal of Wildland Fire ◽

10.1071/wf19114 ◽

2020 ◽

Vol 29 (7) ◽

pp. 611

Author(s):

Breeanne K. Jackson ◽

S. Mažeika P. Sullivan

Keyword(s):

Sierra Nevada ◽

Riparian Vegetation ◽

Fire Severity ◽

Riparian Ecosystems ◽

High Severity ◽

Sediment Size ◽

Rim Fire ◽

Geomorphic Features ◽

Biodiversity And Ecosystem Function ◽

Riparian Plant

Fires are a common feature of many landscapes, with numerous and complex ecological consequences. In stream ecosystems, fire can strongly influence fluvial geomorphic characteristics and riparian vegetation, which are structural components of stream–riparian ecosystems that contribute to biodiversity and ecosystem function. However, the effects of fire severity on stream–riparian ecosystems in California’s Sierra Nevada region (USA) are not well described, yet critical for effectively informing fire management and policy. At 12 stream reaches paired by fire severity (one high-severity burned, one low-severity burned), no significant differences were found in riparian plant community cover and composition or stream geomorphic characteristics 2–15 years following wildfire. In addition, minimal changes in riparian vegetation and stream geomorphic properties were observed in the first summer following the extensive and severe Rim Fire. However, an upstream-to-downstream influence of multiple fire occurrences was observed over the previous 81 years within each catchment on stream geomorphic metrics, including sediment size, embeddedness and channel geometry, at our study reaches. The inconsistent effects of wildfire on stream–riparian vegetation and geomorphic characteristics over space and time may be related to time since fire and precipitation.

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Mountain Ash

10.1071/9781486304981 ◽

2015 ◽

Cited By ~ 14

Author(s):

David Lindenmayer ◽

David Blair ◽

Lachlan McBurney ◽

Sam Banks

Keyword(s):

Forest Ecosystems ◽

Fire Severity ◽

Fire Dynamics ◽

High Severity ◽

Fire Environment ◽

Arboreal Marsupials ◽

New Findings ◽

Mountain Ash ◽

Old Trees ◽

Very High

Mountain Ash draws together exciting new findings on the effects of fire and on post-fire ecological dynamics following the 2009 wildfires in the Mountain Ash forests of the Central Highlands of Victoria. The book integrates data on forests, carbon, fire dynamics and other factors, building on 6 years of high-quality, multi-faceted research coupled with 25 years of pre-fire insights. Topics include: the unexpected effects of fires of varying severity on populations of large old trees and their implications for the dynamics of forest ecosystems; relationships between forest structure, condition and age and their impacts on fire severity; relationships between logging and fire severity; the unexpectedly low level of carbon stock losses from burned forests, including those burned at very high severity; impacts of fire at the site and landscape levels on arboreal marsupials; persistence of small mammals and birds on burned sites, including areas subject to high-severity fire, and its implications for understanding how species in this group exhibit post-fire recovery patterns. With spectacular images of the post-fire environment, Mountain Ash will be an important reference for scientists and students with interests in biodiversity, forests and fire.

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Avian Response to Wildfire Severity in a Northern Boreal Region

Forests ◽

10.3390/f11121330 ◽

2020 ◽

Vol 11 (12) ◽

pp. 1330

Author(s):

Michelle Knaggs ◽

Samuel Haché ◽

Scott E. Nielsen ◽

Rhiannon F. Pankratz ◽

Erin Bayne

Keyword(s):

Climate Change ◽

Species Richness ◽

Functional Diversity ◽

Vegetation Type ◽

Fire Severity ◽

Natural Disturbance ◽

Burn Severity ◽

Vegetation Types ◽

Generalist Species ◽

High Severity

Research Highlights: The effects of fire on birds in the most northern parts of the boreal forest are understudied. We found distinct differences in bird communities with increasing fire severity in two vegetation types with naturally different burn severity. The highest severity burns tended to have communities dominated by generalist species, regardless of the original vegetation type. Background and Objectives: Wildfire is the primary natural disturbance in the boreal ecosystems of northwestern Canada. Increased wildfire frequency, extent, and severity are expected with climate change in this region. In particular, the proportion of burns that are high severity and the area of peatlands burned are increasing, and how this influences birds is poorly understood. Materials and Methods: We quantified the effects of burn severity (low, moderate, and high severity) in uplands and peatlands on occupancy, density, richness, community composition, and functional diversity using point counts (n = 1158) from the first two years post-fire for two large fires in the Northwest Territories, Canada. Results: Burn severity had a significant effect on the occupancy and density of 86% of our focal species (n = 20). Responses to burn severity depended on vegetation type for four of the 18 species using occupancy and seven of the 18 using density, but were typically in a similar direction. Species richness and functional diversity were lower in areas of high severity burns than unburned areas and low severity burns in peatlands. Richness was not related to severity in uplands, but functional diversity was. Peatlands had higher species richness than uplands in all burn severities, but as burn severity increased the upland and peatland communities became more similar. Conclusions: Our results suggest that high severity burns in both vegetation types support five generalist species and two fire specialists that may benefit from alterations in vegetation structure as a result of climate induced changes to fire regimes. However, eight species avoided burns, particularly birds preferring peatlands, and are likely to be more susceptible to fire-driven changes to their habitat caused by climate change. Understanding the long-term risks to these species from climate change requires additional efforts that link fire to bird populations.

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Event-Based Integrated Assessment of Environmental Variables and Wildfire Severity through Sentinel-2 Data

Forests ◽

10.3390/f10111021 ◽

2019 ◽

Vol 10 (11) ◽

pp. 1021 ◽

Cited By ~ 1

Author(s):

Juan Picos ◽

Laura Alonso ◽

Guillermo Bastos ◽

Julia Armesto

Keyword(s):

Land Cover ◽

Forest Fires ◽

Fire Suppression ◽

Fire Severity ◽

Environmental Parameters ◽

Weather Conditions ◽

Integrated Approach ◽

Policy Makers ◽

Event Based ◽

Sentinel 2

To optimize suppression, restoration, and prevention plans against wildfire, postfire assessment is a key input. Since little research has been carried out on applying Sentinel-2 imagery through an integrated approach to evaluate how environmental parameters affect fire severity, this work aims to fill this gap. A set of large forest fires that occurred in northwest Spain during extreme weather conditions were adopted as a case study. Sentinel-2 information was used to build the fire severity map and to evaluate the relation between it and a set of its driving factors: land cover, aspect, slope, proximity to the nearest stream, and fire recurrence. The cover types most affected by fire were scrubland, rocky areas, and Eucalyptus. The presence of streams was identified as a major cause of the reduced severity of fires in broadleaves. The occurrence of fires in the past is linked to the severity of fires, depending on the land cover. This research aims to help fire researchers, authority managers, and policy makers distinguish the conditions under which the damage by fire is minimized and optimize the resources allocated to restoration and future fire suppression.

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Fire damage, mortality, and suckering in aspen

Canadian Journal of Forest Research ◽

10.1139/x87-168 ◽

1987 ◽

Vol 17 (9) ◽

pp. 1100-1109 ◽

Cited By ~ 76

Author(s):

James K. Brown ◽

Norbert V. DeByle

Keyword(s):

Logistic Regression ◽

Regression Analysis ◽

Tree Mortality ◽

Fire Severity ◽

Fire Damage ◽

Bark Thickness ◽

Breast Height ◽

High Severity ◽

Tree Number ◽

Fire Characteristics

Relationships among fire characteristics, fire damage, tree mortality, and sucker response in Populustremuloides Michx. are described. Circumference charred averaged more than 75% on trees killed and less than 50% on live trees. Average char heights ranged from 0.5 m in low severity fire to 1.5 m in high severity fire. Logistic regression analysis showed that probability of mortality was strongly related to diameter at breast height (dbh), char height, and circumference charred. Char heights of 30 cm had a 90% probability of killing aspen less than 25 cm dbh. Bark thickness at breast height and 10 cm aboveground, which relates to fire resistance, related strongly to tree dbh. Bark thickness was the same at sidehill, downhill, and uphill positions. Minimal flame heights required to kill aspen with 90% probability ranged from 10 cm for a 10-cm dbh tree to 60 cm for a 25-cm dbh tree. Number of suckers per hectare on three burns varied from 9 880 to 57 570 the 1st year following fire and from 7 060 to 21 240 4 years after the fire. Depth of sucker origin ranged from 0.2 to 18 cm and was related to fire severity. Sucker density varied greatly between plots and was not significantly related to fire severity.

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