Abstract
Fire-on-fire interactions, where a fire encounters the perimeter and burned area of a previous fire, will increase if large fires become more frequent across the western US. Where fires are limited in size by previous fires, this could improve land and fire management and lower fire suppression costs. We analyzed fire perimeters recorded for 9.7 million forested ha of the U.S. Northern Rockies from 1900 to 2014 to examine fire-on-fire interactions by landscape characteristics and different fire and land management strategies. Less than 10% of the total area burned more than once. We found that fire overlapped more during regional fire years, in wilderness, in dry forests, in the late fire management era (1974-2014), with increasing years since previous fire events and at higher elevation. Distance between fires increased as aspect moved from north-northeast to south-southwest. Fire-on-fire interactions did not vary significantly with slope. Our findings based on analyses of a large area, including both wilderness and non-wilderness, and over a long time frame support for conclusions from previous studies largely limited to wilderness areas and ~30 years of satellite imagery. Fire extent is limited by previous fires on the landscape