Fire refugia, sometimes referred to as fire islands, shadows, skips, residuals, or fire remnants, are an important element of the burn mosaic, but we lack a quantitative framework that links observations of fire refugia from different environmental contexts. Based on what we know of fire refugia from existing studies, we developed and tested a set of hypotheses reflecting the role of topographic factors and fire weather conditions in supporting the occurrence and predictability of refugia. Fire refugia were quantified as areas unburned or burned at comparatively low severity based on remotely sensed burn severity data. We assessed the relationship between fire refugia and a suite of terrain-related explanatory metrics by fitting a collection of boosted regression tree models. The models were developed for seven study fires that burned in conifer-dominated forested landscapes of the Western Cordillera of Canada between 2001 and 2014. We fit nine models, each for distinct levels of fire weather and topographic complexity.
Our analyses showed the overall predictability of contemporary fire refugia varies along gradients of topographic complexity and fire weather conditions, and the relative importance of specific topographic factors differs among broad classes of these environmental measures. We observed highest predictability under moderate fire weather conditions and moderate terrain complexity, and lowest predictability in flatter landscapes and under high fire weather conditions. Catchment slope, local aspect, relative position, topographic wetness, topographic convergence, and local slope all contributed to discriminating where fire refugia occur but the relative importance of these topographic controls differed among environments. Our work advances understanding of the predictability, structure, and function of topographic fire refugia as a component of contemporary burn mosaics in western North American forest ecosystems. From an applied perspective, identifying more probable locations of topographic fire refugia in forested landscapes can inform planning and action for forest harvest, fire operations, landscape restoration, and conservation.