Long-Term Effects of Fire on Vegetation Structure and Predicted Fire Behavior in Wyoming Big Sagebrush Ecosystems

Fire historically occurred across the sagebrush steppe, but little is known about how patterns of post-fire fuel accumulation influence future fire in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) communities. To quantify change in fuel composition and structure in intact sagebrush ecosystems, we sampled 17years following prescribed fire in eight approximately 400ha plots (4 burned, 4 unburned control) at Hart Mountain National Antelope Refuge, OR, USA. Fuels data were used to model potential fire behavior in burn and control plots across four environmental scenarios that mimic drying of fuels through the fire season. Seventeen years after fire total fuel loads were 7xhigher in controls (6015kgha(-1)) than burned plots (831kgha(-1); P<0.01). Herbaceous fuels were 5 times greater in burns (P<0. 01). Shrub fuel was nearly 10 times higher in unburned plots (P<0.01), and litter under shrubs in controls was 3.75 times greater than in burns (P<0.01). Potential fire behavior was lower in burned plots than in unburned controls across all environmental scenarios. In the driest scenario, potential rate of spread ranged from 0.4 to 1.5mmin(-1) in burns and 2.7 to 5.5mmin(-1) in controls (P<0.01). Maintaining resilience in these ecosystems at multiple spatial and temporal scales may include a consideration of the natural role of fire in good condition Wyoming big sagebrush ecosystems. This study shows that under these conditions, fire can promote good condition mid-successional ecosystems and can act as a fuel break, slowing the spread and decreasing the intensity of a future wildfire.