Historical fire in sagebrush landscapes of the Gunnison sage-grouse range from land-survey records

Abstract

We use land-survey records to reconstruct historical fire and landscapes in the current range of the Gunnison sage-grouse (GUSG; Centrocercus minimus), which is proposed for listing under the Endangered Species Act. Using section-line descriptions from 1872 to 1892 surveys, and fire indicators, we reconstructed 110 potential fire patches and 76 fires over about 219,000 ha of sagebrush. The fire-size distribution was inverse-J shaped with a geometric mean patch size of 154 ha and fire size of 212 ha. Historical fire rotations were 178–357 years in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and 90–143 years in mountain big sagebrush (A. tridentata ssp. vaseyana). Fires left little interior unburned area (<4%). Infrequent fires >10,000 ha created expansive grass-dominated vegetation followed by extended recovery and dominance by mature sagebrush. Historical landscapes contained large contiguous expanses of mature sagebrush, structured by variations in density and patches of trees. Dense sagebrush covered 20%, scattered sagebrush 15%, and sagebrush with scattered trees 19% of the area, likely representing natural tree fluctuation in sagebrush and slow post-fire recovery in adjoining woodlands. Preserving large expanses of contiguous sagebrush is consistent with historical fire and recent fragmentation of sagebrush habitat. Treatments to thin and reduce sagebrush appear unnecessary.