Fuels & Fuel Treatments
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It is clear that the state of knowledge based on empirical evidence is at its infancy. This is likely because of the vast challenges associated with designing and implementing sampling designs that account for combinations of spatial and temporal configurations prior to wildfire occurrence. We also suspect part of the reason empirical evidence is lacking is because the distinction between site-level and landscape-level effects is not well recognized in the literature. All papers used the term landscape, but rarely defined the landscape, and some specified identifying landscape-level effects that were truly site-level effects. Future research needs to develop innovative ways to interpret the role of fuel treatments at the landscape level to provide insight on strategic designs and approaches to maximize fuel treatment effectiveness.
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Nonnative species can be introduced or exacerbated by fire and fuels treatments. This resource describes how this can happen and what can be done to minimize the occurrence of nonnative species on burned sites or following fuels management.
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Maximizing the effectiveness of fuel treatments at the landscape scale is a key research and management need given the inability to treat all areas at risk from wildfire, and there is a growing body of scientific literature assessing this need. We synthesized existing scientific literature on landscape-scale fuel treatment effectiveness in North American ecosystems through a systematic literature review. We identified 127 studies that addressed this topic using one of three approaches: simulation modeling, empirical analysis, or case studies. Of these 127 studies, most focused on forested landscapes of the western United States. Together, they generally provided evidence that fuel treatments reduced negative outcomes of wildfire and in some cases promoted beneficial wildfire outcomes, although these effects diminished over time following treatment and were influenced by factors such as weather conditions at the time of fire. The simulation studies showed that fuel treatment extent, size, placement, timing, and prescription influenced the degree of effectiveness.
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Historical wildfire ignition locations and NOAA’s hourly time series of surface weather at 2.5 km resolution are used to drive ELMFIRE to produce wildfire hazards representative of the 2022 and 2052 conditions at 30 m resolution, with the future weather conditions scaled to the IPCC CMIP5 RCP4.5 model ensemble predictions. Winds and vegetation were held constant between the 2022 and 2052 simulations, and climate change’s impacts on the future fuel conditions are the main contributors to the changes observed in the 2052 results. Non-zero wildfire exposure is estimated for 71.8 million out of 140 million properties across CONUS. Climate change impacts add another 11% properties to this non-zero exposure class over the next 30 years, with much of this change observed in the forested areas east of the Mississippi River. “Major” aggregate wildfire exposure of greater than 6% over the 30-year analysis period from 2022 to 2052 is estimated for 10.2 million properties. The FSF-WFM represents a notable contribution to the ability to produce property-specific, climate-adjusted wildfire risk assessments in the US.
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Cows were fitted with VF collars (calves not collared) that use Global Positioning System positioning to contain cattle inside fuel break boundaries and record animal locations at 5-min intervals. End-of-trial forage utilization was 48.5% ± 3.7% and 5.5% ± 0.7% for areas inside and outside of the fuel break, respectively. Daily percentage of cattle locations inside the fuel break was initially > 94% but declined to approximately 75% by the end of the trial. Percentage daily locations of dry cows and cow/calf pairs inside the fuel break was 98.5% ± 0.5% and 80.6% ± 1.1%, respectively (P < 0.001). Our data suggest virtual fencing can be a highly effective method of concentrating grazing to reduce herbaceous fuel biomass within linear fuel breaks. Efficacy of this method could be substantially impacted by use of dry versus cow/calf pairs.
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We evaluated plant community succession following prescribed fire on Artemisia arbuscula var. arbuscula (low sagebrush) steppe in southeastern Oregon. Treatments were “prescribed burned” (burn; fall 2012) and “unburned” (control) low sagebrush a steppe, and the study design was a randomized complete block with 4 replicates per treatment. Herbaceous yield and vegetation canopy cover and density were compared between treatments (2012–2020). Fire practically eliminated low sagebrush and there was no recruitment of new plants in the first 8 years after burning. Herbaceous yield in the burn treatment was about double the control for most of the postfire period. Native perennial grasses and forbs constituted 94% to 96% and Bromus tectorum L. (cheatgrass) 0.2% to 2% of total herbaceous yield in the control. In the burn treatment, perennial grasses and forbs constituted 83% to 87%, native annual forbs 2% to 5%, and cheatgrass 3% to 9% of total herbaceous yield. Despite an increase in cheatgrass, the burned low sagebrush sites were dominated by herbaceous perennial grasses and forbs and exhibited high levels of resilience and resistance. After prescribed fire, for the study sites and comparable low sagebrush associations, weed control or seeding are not necessary to recover the native herbaceous community. However, the results in our study are for low-severity prescribed fire in intact low sagebrush plant communities. Higher-severity fire, as might occur with wildfire, and in low sagebrush communities having greater prefire invasive weed composition should not be assumed to develop similarly high levels of community resilience and resistance.
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In 2006, we initiated fuel reduction treatments (prescribed fire, mowing, and herbicide applications [tebuthiuron and imazapic]) in six Artemisia tridentata ssp. wyomingensis communities. We evaluated long-term effects of these fuel treatments on: (1) magnitude and longevity of fuel reduction; (2) Greater sage-grouse habitat characteristics; and (3) ecological resilience and resistance to invasive annual grasses. Responses were analyzed using repeated-measures linear mixed models. Response variables included plant biomass, cover, density and height, distances between perennial plants, and exposed soil cover. Prescribed fire produced the greatest reduction in woody fuel over time. Mowing initially reduced woody biomass, which recovered by year 10. Tebuthiuron did not significantly reduce woody biomass compared to controls. All woody fuel treatments reduced sagebrush cover to below 15% (recommended minimum for Greater Sage-grouse habitat), but only prescribed fire reduced cover to below controls. Median mowed sagebrush height remained above the recommended 30 cm. Cheatgrass (Bromus tectorum) cover increased to above the recommended maximum of 10% across all treatments and controls. Ecological resilience to woody fuel treatments was lowest with fire and greatest with mowing. Low resilience over the 10 posttreatment years was identified by: (1) poor perennial plant recovery posttreatment with sustained reductions in cover and density of some perennial plant species; (2) sustained reductions in lichen and moss cover; and (3) increases in cheatgrass cover. Although 10 years is insufficient to conclusively describe final ecological responses to fuel treatments, mowing woody fuels has the greatest potential to reduce woody fuel, minimize shrub mortality and soil disturbance, maintain lichens and mosses, and minimize long-term negative impacts on greater sage-grouse habitat. However, maintaining ecological resilience and resistance to invasion may be threatened by increases in cheatgrass cover, which are occurring regionally.
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Drawing on recent syntheses of the scientific evidence, this paper examines “myths” commonly used to
oppose climate- and wildfire-adaptation of fire-prone forests. We use an established framework
designed to counter science denial by recognizing the fallacy for each myth. Fallacies are false
arguments; there are several kinds of fallacies, including cherry picking (selecting only a portion of
facts to support a conclusion), false dichotomies or oversimplification (claiming only two possible
outcomes), circular arguments, or straw man (misdirection) arguments. Learning to recognize
logical fallacies and other characteristics of science denial is an essential component of any
assessment of arguments for and against proposed actions
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Recent literature reviews and syntheses provide valuable references for land management practitioners and stakeholders engaged in designing, evaluating, and implementing scientifically credible wildfire- and climate-adaptation strategies. These syntheses are supported by thousands of peer-reviewed articles that evaluated the benefits and constraints of restoring fire to fire-dependent forest landscapes. This working paper summarizes key insights from the review of studies, described in detail below, that documented unprecedented, human-caused fire exclusion and its impacts on fire-dependent forest landscapes in western North America.
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This review and analysis of the relevant scientific literature on the subject suggest that fuel characteristics have a gradual diminishing effect on the rate of fire spread in forest and shrubland fuel types with increasing fire danger, with the effect not being observable under extreme fire danger conditions. Empirical-based fire spread models with multiplicative fuel functions generally do not capture this effect adequately. The implications of this outcome on fire spread modelling and fuels management are discussed.