Climate drives recent increases in fire activity in aspen ( Populus tremuloides Michx.) forests of the western US

Background Portions of the western US are experiencing simultaneous increases in wildfire frequency, size and intensity alongside worsening drought conditions. Despite the importance of quaking aspen (Populus tremuloides Michx.) as a keystone species, drivers of wildfire in aspen forests remain relatively understudied compared with neighboring vegetation types. Aims Understanding trends and the drivers of wildfire in aspen forests across the western US is crucial for effective monitoring and management. Methods We used Theil–Sen Slope and Mann–Kendall tests of annual area burned to examine wildfire activity in aspen and aspen–conifer forest habitats of the western US over the past 38 years and binomial regressions to understand the climate drivers of wildfire activity. Key results Aspen forest habitats are increasingly burning in more southern ecoregions. Fires occurred when Normalized Difference Moisture Index, Snow Water Equivalent and 100 h fuel moisture were low. Conclusions Fire activity is not increasing in all aspen forests of the western US. Aspen forest habitats are more likely to burn when conditions are dry, supporting the assumption that the typically high moisture content of aspen influences their burn probabilities. Implications These results suggest the need for more specific regional examinations of aspen fire trends to transfer results into effective land management practices.