This synthesis summarizes information available in the scientific literature on presettlement patterns and postsettlement changes in fuels and fire regimes in Wyoming big sagebrush and basin big sagebrush communities. This literature suggests that presettlement fires in the sagebrush biome were both human- and lightning-caused. Peak fire season occurred from April to October and varied geographically. Wildfires were typically stand replacing. Fire frequency was influenced by site characteristics, and frequency estimates ranged from decades to centuries, depending on applicable scales, methods used, and metrics calculated. Because big sagebrush communities occur over a productivity gradient driven by soil temperature and moisture regimes, presettlement fire frequencies likely varied across the gradient, with more frequent fire on more productive sites that supported more continuous fine fuels. Because sites dominated by Wyoming big sagebrush were drier and tended to produce fewer fine fuels, they tended to burn less frequently than sites dominated by mountain big sagebrush, while basin big sagebrush sites tended to be intermediate. Big sagebrush communities adjacent to fire-prone woodland and forest types (e.g., ponderosa pine) may have had more frequent fires than those adjacent to less fire-prone types (e.g., pinyon-juniper woodlands) 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. Large fires were most likely after 1 or more cool, wet years that allowed fine fuels to accumulate and become continuous.

Since European-American settlement, fuel and fire regime characteristics in many big sagebrush communities have shifted outside the range of historical variation. Settlement generally began in the late 1800s and caused changes in ignition patterns and fuel characteristics, although the timing and magnitude of these changes varied among locations. Since then, fuels and fire regimes in many sagebrush ecosystems have changed due to a combination of interrelated factors, including fire exclusion; proliferation of nonnative invasive plants; woodland expansion; overgrazing by livestock; climate changes; land alteration for agriculture and rangeland; and energy, urbanization, and infrastructure development. Since 1980, the number of fires each year and total annual area burned have increased in the sagebrush biome. Limited data suggest that fires have become more frequent in most Wyoming big sagebrush and basin big sagebrush communities, with the exception of communities in the Wyoming Basin ecoregion, where fires may have become less frequent. More frequent fire has been attributed primarily to increased cheatgrass cover and increased human ignitions.