Fire patterns in piñon and juniper land cover types in the semiarid Western United States from 1984 through 2013.
Abstract
Increases in area burned and fire size have been reported across a wide range of forest and shrubland types in the Western United States in recent decades, but little is known about potential changes in fire regimes of piñon and juniper land cover types. We evaluated spatio-temporal patterns of fire in piñon and juniper land cover types from the National Gap Analysis Program using Monitoring Trends in Burn Severity (MTBS 2016) data (1984 through 2013) for Northern and Southern Intermountain and Central and Southern Rocky Mountain geographic regions. We examined differences in total area burned, fire rotation, fire size, fire number, and fire season among: (1) the four geographic regions; (2) the EPA level III ecoregions that occur within each geographic region; and (3) the piñon and juniper land cover types (woodlands, savannas, and shrublands) and other land cover types that occur within each geographic region and level III ecoregion. We found that area burned during the 30-year period, number of fires each year, and fire size followed a strong geographic pattern: Northern Intermountain > Southern Intermountain > Southern Rocky Mountain > Central Rocky Mountain. Area burned within piñon and juniper land cover types increased significantly during the 30-year period across the study area overall and for each geographic region, except the Southern Intermountain. Fire rotations were within reported historical ranges for sagebrush ecosystems and decreased over time. Also, fire number or fire size increased for the Southern Rocky Mountain and Southern Intermountain geographic regions. Across the study area, spatio-temporal patterns in fire regimes for piñon and juniper land cover types were similar to those for other land cover types. Careful monitoring of longer term trends in fire activity and the interacting effects of invasive annual grasses, bark beetles, and climate change is needed to access the dynamics of piñon and juniper land cover types and evaluate the efficacy of management treatments in piñon and juniper land cover types.