Synthesis / Tech Report
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This synthesis summarizes information available in the scientific literature on historical patterns and contemporary changes in fuels and fire regimes in mountain big sagebrush communities. This literature suggests that presettlement fires in the sagebrush biome were both lightning- and human-caused. Peak fire season occurred between April and October and varied geographically. Wildfires were high-severity, stand-replacement fires. Fire frequency estimates range from decades to centuries, depending on the applicable scale, methods used, and metrics calculated. Fire frequency was influenced by site characteristics. Because mountain big sagebrush communities occur over a productivity gradient driven by soil moisture and temperature regimes, fire regimes likely varied across the gradient, with more frequent fire on more productive sites that supported more continuous fine fuels. Sites dominated by mountain big sagebrush burned more frequently than sites dominated by Wyoming big sagebrush, because the former tend to be more productive. Mountain big sagebrush communities adjacent to fire-prone forest types (e.g., ponderosa pine) may have had more frequent fires than those adjacent to less fire-prone types (e.g., pinyon-juniper) and those far from forests and woodlands. Most fires were likely small (less than ~1,200 acres (~500 ha)), and large fires (>24,000 acres (10,000 ha)) were infrequent. Historically, large fires in big sagebrush were most likely after one or more relatively wet years or fire reseasons that favored growth of associated grasses, allowing fine fuels to accumulate and become more continuous.
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The Fuels Guide and Database (FGD) is intended to provide fuel loading and vegetation information for big sagebrush (Artemisia tridentata) ecological sites in the Morley Nelson Snake River Birds of Prey National Conservation Area (NCA) in southern Idaho. Sagebrush ecosystems in the NCA and throughout much of the Great Basin are highly influenced by non-native plants that alter successional trajectories and promote frequent wildfires, especially due to fine-fuel loadings that are highly variable over time and space. These dynamic fuel conditions can increase uncertainty when attempting to project fire risk and fire behavior. The FGD was developed to help quantify and assess these dynamic fuel loadings, and it provides access to fuels data across a range of conditions, from relatively intact sagebrush-bunchgrass communities to degraded communities dominated by nonnative annual grasses and forbs. The FGD can be queried for a variety of environmental conditions, and it provides tabular data, reports, and photographic records of fuels based on user queries. This report describes the FGD, including overall data content and data-collection methods, as well as instructions for installing and using the database.
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To assess the effects of aerial and drill seeding on plant community trajectories, fuel composition, and fire regimes, this study collected geospatial datasets spanning 209,000 ha of sagebrush steppe on BLM land in southern Idaho. In the field, 68 sites were sampled for fuel and plant community composition in 2014 and 2015 across areas that had burned 1-6 times and had no, aerial, drill, or aerial + drill seeding. The study found that 1) fire and rehabilitation shaped plant communities, 2) drill seeding after multiple fires in dry, low elevation sites prevented conversion to cheatgrass-dominated systems, 3) drill seeded sites had fewer fires and increased in fire frequency more slowly than aerial seeded sites, 4) the on-the-ground conditions that led to the decision to aerially seeding after a fire led to more frequent and numerous fires.
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Using epidemiology studies to understand the exposure-response relationship for PM, this study found that firefighters were at an increased risk for long-term health effects from smoke exposure. The risk for lung cancer mortality increases nearly linearly with exposures over time and is more strongly influenced by exposure duration than are the risks of death from cardiovascular or ischemic heart disease. On the other hand, the risk of cardiovascular mortality rises steeply for doses in the range we estimated for firefighter exposures but flattens out at higher exposures to PM. The data presented in this paper clearly identify the crews and activities most likely to exceed occupational exposure limits and firefighters may have a an increased health risk from smoke exposures.
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Mixed severity wildfires burn large areas in western North America forest ecosystems in most years and this is expected to continue or increase with climate change. Little is understood about vegetation recovery and changing fuel conditions more than a decade post-fire because it exceeds the duration of most studies of fire effects. We measured plant species composition, conifer seedling regeneration, fuel loads, and ground cover at 15 wildfires that burned 9-15 years previous in five western U.S. vegetation types distributed across eight states including Alaska.
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This report contains descriptions of USGS sage-grouse and sagebrush ecosystem research projects that are ongoing or were active during 2018 and is organized into five thematic areas: Fire, Invasive Species, Restoration, Sagebrush, Sage-Grouse, and Other Sagebrush-Associated Species; and Climate and Weather.
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Data on plant cover and density was collected on 67 sites in a 209,000 ha study area that varied in fire and post-fire rehabilitation history along gradients in elevation, soil texture, and precipitation. Multiple linear regression indicated significant inverse relationships between B. tectorum and both P. secunda and A. cristatum, but P. secunda had suppressed B. tectorum cover and density better than A. cristatum. A nonparametric multiple regression analyzing the effect of 86 abiotic and biotic independent variables indicated that elevation, mid to late season native perennial bunchgrasses, and the number of post-fire rehabilitation treatments (for B. tectorum cover) or time since most recent rehabilitation (for B. tectorum density) explained the most variation in Bromus tectorum suppression across the landscape.
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This Rangelands on the Edge (ROTE) project improves our understanding of the fate of rangelands from historical, present day, and future perspectives by describing human modification, fragmentation, and future residential growth projections for rangeland-dominated vegetation. Since pre-European settlement, some 340 million acres (over 34 percent) of rangelands, particularly in the Great Plains, have been converted to alternative land uses, especially intensive agriculture (croplands, pastureland). Approximately 11 percent of private rangelands are likely to experience significant increases in housing development over the next 15 years.
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This report presents a new fuel sampling method, called the photoload sampling technique, to quickly and accurately estimate loadings for six common surface fuel components (1 hr, 10 hr, 100 hr, and 1000 hr downed dead woody, shrub, and herbaceous fuels). This technique involves visually comparing fuel conditions in the field with photoload sequences to estimate fuel loadings. Photoload sequences are a series of downward-looking and close-up oblique photographs depicting a sequence of graduated fuel loadings of synthetic fuelbeds for each of the six fuel components.
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The original objective of the study was to determine how ignition, smoldering, and flaming are affected by the age of masticated fuels using a combined field and lab approach.