Topographic and fire weather controls of fire refugia in forested ecosystems of northwestern North America

Abstract

Abstract. 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. Here, we develop and test a conceptual model for how predictability of fire refugia varies according to topographic complexity and fire weather conditions. Refugia were quantified as areas unburned or burned at comparatively low severity based on remotely sensed burn severity data. We assessed the relationship between 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 terrain ruggedness. Our framework revealed that the predictability and abundance of fire refugia varied among these environmental settings. We observed highest predictability under moderate fire weather conditions and moderate terrain ruggedness (ROC-AUC = 0.77), and lowest predictability in flatter landscapes and under high fire weather conditions (ROC-AUC = 0.63-0.68). Catchment slope, local aspect, relative position, topographic wetness, topographic convergence, and local slope all contributed to discriminating where refugia occur but the relative importance of these topographic controls differed among environments. Our framework allows us to characterize the predictability of contemporary fire refugia across multiple environmental settings and provides important insights for ecosystem resilience, wildfire management, conservation planning, and climate change adaptation.

Characterizing Spatial Neighborhoods of Refugia Following Large Fires in Northern New Mexico USA

“…Decreasing density of refugia may occur in places where mechanisms such as environmental setting (e.g., cooler or wetter microclimates; topographic position) are insufficient to maintain patterns of refugia observed following earlier fire events. Furthermore, protection afforded by terrain can be lessened under severe fire weather [11].…”

“…Moreover, examining additional factors that interact to define refugial environments remains a key priority and could serve to improve the limited explanatory power of the models we developed specifically for our study landscape. These factors include the temporal progress of burning and associated fire weather that have been shown to shape refugial environments [11]. Future development and tests of new indices derived from remotely sensed data could also result in improved understanding of refugial characteristics following fire events.…”

“…Many studies have focused on identifying refugia through establishing a link to topographic heterogeneity (e.g., [9][10][11]). Specifically, refugia may be found where fire interacts with stable landscape features that influence microclimate, reduce flammability or create topographic or hydrologic barriers to fire spread [4,[12][13][14][15].…”

Recognizing Women Leaders in Fire Science

“…Her notable works include projections of future global geographic distributions of wildfires [158] and furthering the understanding of the biotic and abiotic constraints on fire occurrence [159,160]. Her recent works have included further understanding the spatial patterns of burned areas, refugia, and fire occurrence [161][162][163] and contributions to a synthesis calling for more adaptation to wildfires in western North American forests [14].…”

“…Her notable research includes furthering the understanding of scaling when considering fire regimes [189] and synthesizing risk analysis approaches used in wildland fire management [190]. Her recent works have included assessing refugia following large fires [161,191] and a synthesis of progress in wilderness fire science [192].…”