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Human-dominated pyromes (85% mean anthropogenic ignitions), with moderate fire size, area burned, and intensity, covered 59% of CONUS, primarily in the East and East Central. Physically dominated pyromes (47% mean anthropogenic ignitions) characterized by relatively large (average 439 mean annual ha per 50 km pixel) and intense (average 75 mean annual megawatts/pixel) fires occurred in 14% of CONUS, primarily in the West and West Central. The percent of anthropogenic ignitions increased over time in all pyromes (0.5–1.7% annually). Higher fire frequency was related to smaller events and lower FRP, and these relationships were moderated by vegetation, climate, and ignition type. Notably, a spatial mismatch between our derived modern pyromes and both ecoregions and historical fire regimes suggests other major drivers for modern U.S. fire patterns than vegetation-based classification systems. This effort to delineate modern U.S. pyromes based on fire observations provides a national-scale framework of contemporary fire regions and may help elucidate patterns of change in an uncertain future.
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In this Research-Partnership Highlight, we argue that private-public partners in such settings must be strategic in their selection of tasks to generate “small wins” in order to build the trust, competency, and legitimacy needed to advance an approach for landscape-scale fine fuels management. We highlight a fine fuels reduction partnership consisting of public and private entities in southeastern Oregon that established a research and education project and applied dormant season grazing on three pastures within the Vale District Bureau of Land Management. We describe the impetus for the partnership, antecedents, strategic tactics, and ongoing learning and reflection used to revise processes. In this example, implementing dormant season grazing as a research and education project allowed the partners to assess the efficaciousness of the treatment, as well as the operational logistics and administrative competencies necessary to apply the treatment to manage fine fuels at broader scales. Because dormant season grazing may, in some instances, conflict with established practices and norms, small-scale projects such as this allow partners to refine understandings of the social and administrative conditions that make implementation possible. Generating small wins through projects such as this is a critical precursor for partnerships seeking to take on larger, more complex endeavors that involve increasing ecological, economic, and social uncertainty.
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We modeled seasonal habitat use by female greater sage-grouse in the Trout Creek Mountains of Oregon and Nevada, USA, to identify landscape characteristics that influenced sage-grouse habitat selection and to create predictive surfaces of seasonal use 1 and 7 years postfire. We developed three resource selection function models using GPS location data from 2013 to 2019 for three biologically distinct seasons (breeding, n = 149 individuals: 8 March–12 June; summer, n = 140 individuals: 13 June–20 October; and winter, n = 94 individuals: 21 October–7 March). For all seasons, by the fourth or fifth year postfire, sage-grouse selected for unburned patches more than all other burn severity patches and the use of unburned areas in comparison with burned areas increased through time. During the breeding season, sage-grouse selected for low-sagebrush -dominated ecosystems and areas with low biomass (normalized difference vegetation index). During summer, sage-grouse selected for areas with higher annual and perennial grasses and forb cover, and areas that had higher biomass. During winter, sage-grouse selected for areas of intact sagebrush on less rugged terrain. For the winter and breeding season, there was a positive linear relationship between annual grasses and forb cover through time. Seven years postfire (2019), the area predicted to have a high probability of use in each seasonal range decreased (breeding: 16.4%; summer: 12.2%; and winter: 4.2%), while the area predicted to have low or low-medium probability of use increased (breeding: 14.5%; summer: 22.5%; and winter: 22.8%) when compared to the first year following the wildfire (2013). Our results demonstrated a 4- to 5-year time lag before female sage-grouse adapted to a disturbed landscape began avoiding burned areas more than intact, unburned habitats. This mismatch in ecological response may imply declines in habitat availability for sage-grouse and may destabilize population vital rates. Spatially explicit models can aid in identifying priority areas for restoration efforts and conservation actions to mitigate the impacts of future disturbances.
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We measured the presence of greater sage-grouse (GRSG) scat and modeled the probability of GRSG presence (PrGRSG-scat) in relation to variation in plot-level and landscape-level predictors, and land treatments, in an intensive, repeat sampling from 2017 to 2020 of 113,000 ha area burned in 2015 in the Soda Megafire (Oregon and Idaho, U.S.A.). GRSG scat was present in less than 200 of more than 8,000 observations, as would be expected for a philopatric species (i.e. high fidelity to home site) returning to degraded habitat. PrGRSG-scat was positively associated with sagebrush presence at the plot level and was positively related to elevation, lower-angle slopes, and proximity to sagebrush seedling outplant islands. The statistical significance of relationships of PrGRSG-scat to restoration treatments was marginal at best, with the largest effect being a positive response of PrGRSG-scat to pre-emergent herbicide sprayed to reduce exotic annual grasses. More time may be required for restored sagebrush steppe to meet GRSG needs or for GRSG to “adopt” the restored vegetation. Moreover, whereas scat is a convenient and non-invasive method to monitor GRSG, its post-fire scarcity weakens the strength of statistical inference on GRSG recovery patterns and response to restoration.
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Field data from 460 sagebrush populations sampled across the Great Basin revealed several patterns. Sagebrush seedlings were uncommon in the first 1–2 years after fire, with none detected in 69% of plots, largely because most fires occurred in areas of low resistance to invasive species and resilience to disturbance (hereafter, R&R). Post-fire aerial seeding of sagebrush dramatically increased seedling occupancy, especially in low R&R areas, which exhibited a 3.4-fold increase in occupancy over similar unseeded locations. However, occupancy models and repeat surveys suggested exceptionally high mortality, as occupancy rates declined by as much as 50% between the first and second years after fire. We found the prevalence of “fertile island” microsites (patches beneath fire-consumed sagebrush) to be the best predictor of seedling occupancy, followed by aerial seeding status, native perennial grass cover, and years since fire. In populations where no sagebrush seeding occurred, seedlings were most likely to occur in locations with a combination of high fertile island microsite cover and close proximity to a remnant sagebrush plant. These important attributes were only present in 13% of post-fire locations, making them rare across the Great Basin.
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We sought to forecast future shifts in rangeland growing season timing due to climate change, and interpret their importance for land management and ecosystem function. We trained a model on remotely sensed land surface phenology and climate data collected from 2001 to 2014 in temperate United States rangelands. We used this model to forecast annual growing season start dates, end dates, and season length through 2099 among six general circulation models and under RCP 4.5 and 8.5 scenarios. Growing season start was projected to shift earlier throughout our study area. In 2090-2099, start of season advanced by an average of 10 (RCP 4.5) to 17 (RCP 8.5) days. End of season also advanced by 12 (RCP 4.5) to 24 (RCP 8.5) days, but with greater heterogeneity. Start and end of season change mainly offset one another, so growing season length changes were lesser (2 days in RCP 4.5, and 7 in RCP 8.5). Some mountainous areas experienced both earlier start of season and later end of season, lengthening their growing season. Earlier phenology in rangelands would force adaptation in grazing and impact ecosystem function. Mountainous areas with earlier start and later end of season may become more viable for grazing, but most areas may experience slightly shortened growing seasons. Autumn phenology warrants greater research, and our finding of earlier autumn senescence contradicts some prior research.
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The magnitude of impact of tree encroachment on rangeland loss is similar to conversion to cropland, another well-known and primary mechanism of rangeland loss in the US Prioritizing conservation efforts to prevent tree encroachment can bolster ecosystem and economic sustainability, particularly among privately-owned lands threatened by land-use conversion.
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Forest biological disturbance agents (BDAs) are insects, pathogens, and parasitic plants that affect tree decline, mortality, and forest ecosystems processes. BDAs are commonly thought to increase the likelihood and severity of fire by converting live standing trees to more flammable, dead and downed fuel. However, recent research indicates that BDAs do not necessarily increase, and can reduce, the likelihood or severity of fire. This has led to confusion regarding the role of BDAs in influencing fuels and fire in fire-prone western United States forests. Here, we review the existing literature on BDAs and their effects on fuels and fire in the western US and develop a conceptual framework to better understand the complex relationships between BDAs, fuels and fire. We ask: 1) What are the major BDA groups in western US forests that affect fuels? and 2) How do BDA-affected fuels influence fire risk and outcomes? The conceptual framework is rooted in the spatiotemporal aspects of BDA life histories, which drive forest impacts, fuel characteristics and if ignited, fire outcomes. Life histories vary among BDAs from episodic, landscape-scale outbreaks (bark beetles, defoliators), to chronic, localized disturbance effects (dwarf mistletoes, root rots). Generally, BDAs convert aboveground live biomass to dead biomass, decreasing canopy fuels and increasing surface fuels. However, the rate of conversion varies with time-since-event and among BDAs and forest types, resulting in a wide range of effects on the amount of dead fuels at any given time and place, which interacts with the structure and composition of the stand before and subsequent to BDA events. A major influence on fuels may be that BDAs have emerged as dominant agents of forest heterogeneity creation. Because BDAs play complex roles in fuels and fire heterogeneity across the western US which are further complicated by interactions with climate change, drought, and forest management (fire suppression), their impacts on fuels, fire and ecological consequences cannot be categorized simply as positive or negative but need to be evaluated within the context of BDA life histories and ecosystem dynamics.
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Soil temperature extremes are not uncommon when woody fuels are ignited in prescribed burns or wildfires. Whether this leads to substantial loss of soil organic matter or microbial life is unclear. We created a soil heat gradient by burning four levels of masticated woody fuels (0, 34, 101, and 169 Mg ha−1) to determine if heat thresholds produce abrupt changes in soil C, N, microbial biomass, or fungal hyphae. Twenty-four burns were conducted with masticated fuels overlaying a clay loam soil equilibrated at either 4 or 25% volumetric soil water content. Maximum temperatures ranged from 40 to 450 °C depending on fuel load and soil moisture content, with heat duration (>60 °C) as great as 22 h. Moist soil quenched temperatures two- to threefold compared with dry soil at comparable fuel loads. A slight, gradual decline in total C and N was found with increasing temperature and heat duration, reaching a maximum loss of 14–18% of the total at the highest heat load. Available NH4 increased linearly starting at 150–175 °C and reached a maximum 15-fold increase relative to unburned soil by 450 °C. Nitrification (30 d post-fire) was low regardless of treatment and was essentially eliminated at the highest temperatures. Microbial biomass declined curvilinearly with increased heating, approaching 65% loss compared with unburned soil, and was most rapid in moist soil once temperatures exceeded 60–70 °C. Ultimately, we found no evidence of abrupt heat thresholds for these common soil properties. Instead, property changes followed a slightly declining trajectory (soil C, N, NO3, fungal hyphae) or a steady incremental increase (NH4) or decrease (microbial biomass).
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We found that many community members were initially drawn to learn about wildfre risk mitigation, but their informational needs shifted toward broader forest ecology over time, suggesting that communication strategies and topics must also evolve over time. Some common terms used by land management professionals were unclear to public audiences, sometimes leading to feelings of dissatisfaction with outreach. One-on-one meetings and experiential group learning were perceived by information providers and community members to be useful strategies for outreach. Our fndings can be used to improve ongoing outreach in this study area and inform similar efforts elsewhere.