Temporal Patterns Of Large Wildfires And Their Burn Severity In Rangelands Of Western United States

Wildfires in forest ecosystems have been well studied, while wildfires in rangelands ecosystems have received less attention. This study evaluated temporal trends of large wildfires on rangelands in western United States from 1984 to 2017, using the Monitoring Trends in Burn Severity product (captured wildfires >= 405 ha in size in western United States) and Autoregressive Integrated Moving Average analysis. The results showed a significant increase (more than fivefold) in area of rangeland burned by large wildfires, but generally no significant trends in proportions of areas burned at different levels of severity. The trends for all rangelands, in total area burned and in areas burned at different levels of severity, were most similar to the trends for herbaceous-dominated rangelands but largely different from the trends for shrub-dominated rangelands. These findings can aid in the development of management strategies for anticipating and reducing wildfire risk and enhancing rangeland conservation and sustainability.Plain Language SummaryWildfires have become more frequent and larger in the western United States over the last 30 years. Burn severity, an indicator of fire effects on soil and vegetation, can help in assessing fire impacts on ecosystem structure and function. Many studies have explored burn severity of wildfires in forests, while less attention has been given to rangelands. In this study, we examined temporal trends of large wildfires (=405 ha in size) on rangelands in western United States from 1984 to 2017, in terms of rangeland area burned and areas burned at different levels (low, moderate, and high) of severity using the Monitoring Trends in Burn Severity data. We also tested whether the trends were consistent in three rangeland ecosystem types: grass-dominated, shrub-dominated and treedominated rangelands. The results showed a significant increase in rangeland areas burned over time, but the rate of increase was lower than that for forests. Furthermore, the trends for all rangeland burned were similar to the trends for grass-dominated rangelands but different from the trends for shrub- dominated rangelands. These findings can help policymakers and rangeland managers in developing strategies for anticipating and reducing wildfire risks and enhancing rangeland conservation and sustainability in western United States.