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This study evaluates the implications of ten twenty-first century climate scenarios for snow, soil moisture, and fuel moisture across the conterminous western USA. A decline in mountain snowpack, an advance in the timing of spring melt, and a reduction in snow season are projected for five mountain ranges in the region. The accelerated depletion of mountain snowpack due to warming leads to reduced summer soil moisture across mountain environments. Similarly, warmer and drier summers lead to decreases of up to 25% in dead fuel moisture across all mountain ranges. Collective declines in spring mountain snowpack, summer soil moisture, and fuel moisture across western mountain ranges will increase fire potential in flammability-limited forested systems where fuels are not limiting.
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This meta-analysis was conducted to determine if there were consistent responses of understory vegetation to fire and thinning treatments in North American forests that historically experienced frequent surface fire regimes (<20 year fire-return interval, FRI). The most consistent effect of the treatments was the increase in non-native species following mechanical thinning and reduction in shrub cover following a burn. These differences suggest the two treatments may not be surrogates in the short-term (less than 5 years). Prescribed fire and thinning treatments can be used successfully to restore understory species richness and cover, but they can create different conditions and these potentially different outcomes need to be considered in the planning of a fuels reduction treatment.
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This study investigated effects of fall grazing, spring grazing and not grazing on fuel characteristics, fire ignition and initial spread during the wildfire season (July and August) at five shrub steppe sites in Oregon, USA. Both grazing treatments decreased fine fuel biomass, cover and height, and increased fuel moisture, and thereby decreased ignition and initial spread compared with the ungrazed treatment. However, the probability of initial spread was 6-fold greater in the fall-grazed compared with the spring-grazed treatment in August. This suggests that spring grazing may have a greater effect on fires than fall grazing, likely because fall grazing does not influence the current year’s plant growth.
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This study compared spring and fall prescribed fires at three sites (native-dominated, Bromus tectorum-dominated, and Juniperus occidentalis-dominated). There were higher plant survival rates following fall fires and native-dominated sites than in spring burns or where exotics dominated. These results show that burn season and prefire condition are important considerations when evaluating management alternatives in Artemisia tridentata ssp. vaseyana ecosystems.
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This study analyzed existing permanent monitoring plot data collected between 1995 and 2010 to assess achievement of management objectives related to prescribed fire in ponderosa pine forests. Following first entry fire, ponderosa pine (Pinus ponderosa var. scopulorum) and Gambel oak (Quercus gambelii) overstory and midstory densities declined between 10% and 45% and effectively shifted the Gambel oak diameter distribution toward larger trees. Second entry fires had a greater effect, reducing ponderosa pine and Gambel oak overstory and midstory densities between 24% and 92%. Diameter distributions of both species shifted toward fewer, larger trees following second entry fires. Total fuel load was reduced by <20% in first entry fires and by half in second entry fires. Several objectives identified by the National Park Service (e.g., overstory ponderosa pine reduction) were not achieved with either fire entry; however, power analysis indicated that sample sizes were not adequate to fully detect long term changes following first entry fires.
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In this study, researchers examined nitrogen cycling rates in sagebrush and cheatgrass-invaded soils over a 100 mile range in the northern Great Basin, adding antibiotics to study the roles that soil fungi and bacteria play in nitrogen transformations. Results point to the important role fungi play in nitrogen dynamics in native sagebrush steppe and suggest that cheatgrass’s alteration of the microbial community may make nitrogen more available further benefiting the establishment and growth of this invasive grass.
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This study used three years of survey data to examine the relationship between gas field development density and pygmy rabbit site occupancy patterns on four major Wyoming gas fields (Continental Divide–Creston–Blue Gap, Jonah, Moxa Arch, Pinedale Anticline Project Area). The study found that pygmy rabbits in southwestern Wyoming may be sensitive to gas field development at levels similar to those observed for greater sage-grouse, and may suffer local population declines at lower levels of development than are allowed in existing plans and policies designed to conserve greater sage-grouse by limiting the surface footprint of energy development. Buried utilities, gas well pads, areas adjacent to well pads, and well pad access roads had the strongest negative correlation with pygmy rabbit presence and abundance. Minimizing the surface footprint of these elements may reduce negative impacts of gas energy development on pygmy rabbits.
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This study examines the drought fire relationship, specifically the correlations between water balance deficit and annual area burned, across the full gradient of deficit in the western USA, from temperate rainforest to desert. In the middle of this gradient, conditional on vegetation (fuels), correlations are strong, but outside this range the equivalence hotter and drier equals more fire either breaks down or is contingent on other factors such as previous year climate. This suggests that the regional drought fire dynamic will not be stationary in future climate, nor will other more complex contingencies associated with the variation in fire extent. Predictions of future wildfire area therefore need to consider not only vegetation changes, as some dynamic vegetation models now do, but also potential changes in the drought fire dynamic that will ensue in a warming climate.
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This study used the ecohydrological simulation model SOILWAT to disentangle the contributions of direct climate change effects and of additional indirect, climate change-induced changes in vegetation on soil water availability. Vegetation change will mostly exacerbate low soil water availability in regions already expected to suffer from negative direct impacts of climate change (with the two RCP scenarios giving us qualitatively similar effects). By contrast, in regions that will likely experience increased water availability due to climate change alone, vegetation changes will counteract these increases due to increased water losses by interception. In only a small minority of locations, climate change-induced vegetation changes may lead to a net increase in water availability. These results suggest that changes in vegetation in response to climate change may exacerbate drought conditions and may dampen the effects of increased precipitation, that is, leading to more ecological droughts despite higher precipitation in some regions. Our results underscore the value of considering indirect effects of climate change on vegetation when assessing future soil moisture conditions in water-limited ecosystems.
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This project examines the weather and climate factors related to known megafires and very large wildfires that have occurred across the contiguous United States and projects the likelihood of megafires occurring during the 2046-2065 mid-century time period. A variety of statistical techniques and spatial scales were used in the analysis. The report ranks regions of future higher likelihood very large fire locations based on overall probability. In addition, the potential for large-scale smoke impact effects from very large fires was examined. This included the overall potential for smoke emissions, as well as the potential for downwind transport to various kinds of sensitive receptors. Combining future very large fire projections with site specific Smoke Impact Potentials allows for the ranking of locations based on the potential for large scale smoke impacts from very large fires.