Fire Regimes
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A group of people knowledgeable about wildland fire have produced a 52-page document that attempts to assemble and summarize areas of agreement and disagreement regarding the management of forested areas in the western United States. Calling themselves the Fire Research Consensus Working Group, they looked for areas of common ground to provide insights for scientists and land managers with respect to recent controversies over the role of low-, moderate-, and high-severity fires.
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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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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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This study evaluated spatio-temporal patterns of fire in piñon and juniper land cover types from the National Gap Analysis Program using Monitoring Trends in Burn Severity (MTBS 2016) data (1984 through 2013) for Northern and Southern Intermountain and Central and Southern Rocky Mountain geographic regions. It also examined differences in total area burned, fire rotation, fire size, fire number, and fire season among: 1) the four geographic regions; 2) the EPA level III ecoregions that occur within each geographic region; and 3) the piñon and juniper land cover types (woodlands, savannas, and shrublands) and other land cover types that occur within each geographic region and level III ecoregion. We found that area burned during the 30-year period, number of fires each year, and fire size followed a strong geographic pattern: Northern Intermountain > Southern Intermountain > Southern Rocky Mountain > Central Rocky Mountain. Area burned within piñon and juniper land cover types increased significantly during the 30-year period across the study area overall and for each geographic region, except the Southern Intermountain.
View Chapter 11 of the book, Exotic brome-grasses in arid and semiarid ecosystems of the western US: causes, consequences, and management implications.
Human land uses are the primary cause of the introduction and spread of exotic annual Bromus species. Initial introductions were likely linked to contaminated seeds used by homesteading farmers in the late 1880s and early 1900s. Transportation routes aided their spread. Unrestricted livestock grazing from the 1800s through the mid-1900s reduced native plant competitors leaving large areas vulnerable to Bromus dominance. Ecosystems with cooler and moister soils tend to have greater potential to recover from disturbances (resilience) and to be more resistant to Bromus invasion and dominance. Warmer and drier ecosystems are less resistant to Bromus and are threatened by altered fire regimes which can lead to Bromus dominance, impacts to wildlife, and alternative stable states.
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Paleovegetation studies show that even prior to anthropogenic influence, sage steppe communities were dynamic, and in some cases, susceptible to replacement by other vegetation communities (including forests) under changing climatic conditions.
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This study reviewed published studies on reburns in fire-adapted ecosystems of the world, including temperate forests of North America, semi-arid forests and rangelands, tropical and subtropical forests, grasslands and savannas, and Mediterranean ecosystems. To date, research on reburns is unevenly distributed across the world with a relative abundance of literature in Australia, Europe and North America and a scarcity of studies in Africa, Asia and South America. This review highlights the complex role of repeated fires in modifying vegetation and fuels, and patterns of subsequent wildfires. In fire-prone ecosystems, the return of fire is inevitable, and legacies of past fires, or their absence, often dictate the characteristics of subsequent fires.
Access the data.
The relationship between climate and wildfire area burned suggests how fire regimes may respond to a changing climate. This West-wide data publication contains a 27-year record (1980-2006) of climatological variables used to develop statistical models of area burned that can be projected into the future. We provide a separate file for each of the 56 Bailey’s ecosections (Bailey 2016) across the West, with annual area burned and 112 climate predictor variables such as evapotranspiration, precipitation, relative humidity, soil moisture, snow-water equivalent, minimum and maximum temperature, and vapor pressure deficit. These historical and future hydroclimate projections and historical fire area burned data were derived for McKenzie and Littell (2016).
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This guide is designed to provide direction on the critique and modification of LANDFIRE geospatial data products for local applications. It is not so much a “cookbook” or “how-to” guide, as the specifics vary greatly by data product, intended use, scale, and location. Rather, it presents primary considerations for using and modifying the data for use in local applications and provide examples and demonstrations of available tools and methods for completing common critique and modification tasks.
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This KQED Science article indicates that since 1600, the way humans have used land in the Sierra has had more effect on fire behavior than climate change. Valerie Trouet, associate professor of dendrochronology at the University of Arizona and lead coauthor of a study about humans and fire, suggests that land managers and owners can affect fire behavior through activities that make forests more resilient.