Pre-Euro-American and Recent Fire in Sagebrush Ecosystems

Abstract

Sagebrush (Artemisia spp.) ecosystems are under threat from a variety of land uses, disturbance, and invasive species, and are also thought by some to have been affected by fire exclusion and require burning as a part of restoration. To better understand the historical range of variation (HRV) of fire in sagebrush ecosystems and whether sagebrush fire regimes today have too much or too little fire, I estimated fire rotation (expected time to burn the area of a landscape) in sagebrush ecosystems under the HRV. Estimates derived from five sources are 200 years in little sagebrush (A. arbuscula), 200–350 years in Wyoming big sagebrush (A. tridentata ssp. wyomingensis), 150–300 years in mountain big sagebrush (A. t. ssp. vaseyana), and 40–230 years in mountain grasslands containing patches of mountain big sagebrush with longer rotations in areas where sagebrush intermixes with forests. Landscape dynamics under the HRV were likely dominated in all sagebrush areas by infrequent episodes of large, high-severity fires followed by long interludes with smaller, patchier fires, allowing mature sagebrush to dominate for extended periods. Fire rotation, estimated from recent fire records, suggests fire exclusion had little effect on fire in sagebrush ecosystems. Instead, cheatgrass (Bromus tectorum), human-set fires, and global warming may have led to too much fire relative to the HRV in four floristic provinces within the range of sagebrush in the western United States. Sagebrush ecosystems would generally benefit from rest from disturbance. Global warming is likely to increase fire, and widespread prescribed burning of sagebrush is unnecessary. Where cheatgrass occurs, fire suppression is sensible. In areas of depleted understories, restoration to reestablish native plants is needed if sagebrush ecosystems are to effectively recover from future disturbance.