Is Wildland Fire Increasing in Sagebrush Landscapes of the Western United States?

Wildland fire is expected to increase with global change, but responses may be spatially heterogeneous and temporally variable, complicating detection. In this study, I analyzed twenty-five years of spatial data on wildfires in woody sagebrush (Artemisia spp.) shrublands across 48 million ha of the Western United States, to test eleven hypotheses about trend and heterogeneity in wildfires. No upward trend in annual area burned was found across the whole study area, consistent with previous simulations that suggest fire may not increase in semiarid shrublands. At a finer scale, a significant trend occurred only in montane sagebrush, of five sagebrush types, and in two of seven floristic provinces. Area burned was concentrated in years with large fires. These years generally lacked or had only a weak trend, comparing two halves of the twenty-five-year period. Sagebrush types did not differ significantly in recent fire rotation, which did differ among floristic provinces and appears shorter now than historic...