Implications of climate change on large fires across spatio-temporal scales in sagebrush steppe

Background/Question/Methods
Throughout the western U.S., sagebrush steppe ecosystems are experiencing an increase in the frequency of wildfires due to an increase of invasive annuals such as cheatgrass, and anthropogenic disturbances, combined with a changing climate. As the impact of climate variability and extreme climatic events on fire occurrence and size can vary depending on scales at which they are analyzed, fire histories were reconstructed across multiple spatial scales. We explored the relationships between fire and climate by investigating a range of potentially important climatic variables in an effort to understand the relationship between seasonal climate patterns and large fire potential in the future. There are few studies of fire history in the sagebrush steppe and none that examine the changes in occurrence of large fires (5 000+ hectares) and consecutive climatic conditions. This study was undertaken to test the hypothesis that climate change will likely influence the occurrence of large fire events by altering disturbance regime and the abundance of invasive species. Using empirical data collected from fire history records, we documented the fire history across three spatial scales. The fire records span 1960 to 2003. To investigate the probability of future regional fire years in sagebrush steppe in response to changes in climate, six hypothetical scenarios were used, where each scenario was simulated as a departure from baseline mean temperature and precipitation. These six scenarios were derived using three downscaled general circulation models (GCMs) and the Intergovernmental Panel on Climate Change (IPCC) A2 and B1 scenarios, which simulate the upper and lower limits of projected greenhouse gasses, respectively. The probability of future regional fire years in sagebrush steppe under different climate scenarios was examined.

Results/Conclusions Preliminary results suggest that the broadest spatial scale experienced higher burn per unit area because of fire suppression at the broad scale, as effects of suppression on fires are not discernable at the finer scales.  Large fires typically occur in areas with high biomass of annuals such as cheatgrass and greater fuel continuity. Fire occurrence is expected to become more frequent with increased drought stress and evapotranspiration due to an increase in summer temperatures in the western U.S. Large fires will occur with increasing frequency as non-native annuals dominate previous sagebrush-dominated lands, increasing fuel loads.