Mountain big sagebrush is a widely distributed shrub native to the western United States. Mountain big sagebrush ecosystems support hundreds of plant and animal species, including several sagebrush obligates. The distribution of mountain big sagebrush has been reduced since European-American settlement, and is likely to be further reduced, due to a variety of causes including conifer establishment, spread of nonnative plants, livestock grazing, and climate change. This review synthesizes the scientific literature on mountain big sagebrush biology and ecology throughout its distribution, with an emphasis on how fire affects the species and how mountain big sagebrush communities respond after fire.
Wildfires in mountain big sagebrush steppe communities are typically high-severity, replacement fires that kill or top-kill most of the aboveground vegetation, although variation in fuels, topography, and weather can produce a patchy mosaic of burned and unburned areas. Mountain big sagebrush plants are easily killed by fire; they do not sprout. The soil seed bank and surviving plants in and adjacent to burns are seed sources for postfire establishment. Most wildfires in sagebrush communities occur in summer and early fall before mountain big sagebrush seeds are ripe. Seeds from surviving plants are typically dispersed within 10 feet (3 m) of parent plants in fall and winter. Seed production is variable, but can be high. Fire characteristics that affect the amount of available seeds (e.g., frequency, severity, season, pattern, and size) can have a strong influence on mountain big sagebrush postfire recovery. Postfire seedling establishment rates vary, but high establishment rates can decrease the amount of time for mountain big sagebrush canopy cover to return to prefire or unburned values (i.e., postfire recovery time).
Mountain big sagebrush postfire recovery time is influenced by a number of interacting factors and varies substantially among sites. Our review and analysis of mountain big sagebrush postfire recovery on 306 burned sites examined in 20 studies found that most available data (86%) comes from burns <25 years old, and that few of these sites (9%) had fully recovered. When site-level data was averaged within 5-year bins, sites tended toward full recovery at 28% canopy cover 26 to 30 years after fire; however, not all burns were fully recovered >25 years after fire. Postfire recovery times varied within and among ecoregions. Mountain big sagebrush communities on cold, moist sites are likely to recover faster and be more resilient to fire and more resistant to postfire nonnative annual grass invasion than those on warm, dry sites, although other factors, such as heavy browsing by wild ungulates, can slow postfire recovery regardless of favorable climate and site characteristics.
There are opposing recommendations about the use of fire in mountain big sagebrush communities. In general, prescribed fire is considered an effective management tool only on sites with greater than ~20% cover of native perennial grasses and forbs, abundant mountain big sagebrush, and little to no cheatgrass or other nonnative plants, if the objective is to reduce mountain big sagebrush cover and increase herbaceous plant production. In areas where native perennial plant cover is depleted, seeding after fire helps stabilize soils, speed recovery of sagebrush and other shrubs, and prevent establishment and spread of nonnative species.