Response to fire by a forest specialist in isolated montane forest

Fire events have increased in scale and severity due to hotter, drier conditions brought on by climate change and fire suppression. Extreme fire events can be detrimental to forest specialists, especially populations at the edge of the species range, where conditions can vary from those within the core of the range. The San Bernardino flying squirrel (Glaucomys oregonensis californicus) is the southernmost subspecies of Humboldt’s flying squirrel and occurs only in the San Bernardino Mountains of southern California after apparent extirpation from the nearby San Jacinto Mountains. We used non-invasive methods to assess how fire affects flying squirrel occupancy. We surveyed for flying squirrels in burned and unburned areas of the San Bernardino Mountains, and measured habitat features to construct occupancy models. Our top models indicated that flying squirrels occupy lower burn severities but could still occur at higher burn severities if canopy cover remained intact, forest duff remained deep, and tree mortality remained low, especially on steeper slopes. Our study illustrates the ability of San Bernardino flying squirrels, and the potential for other flying squirrels, to survive major fire events and maintain their role in the forest ecosystem. Such results are especially important for species management and understanding how parts of an ecosystem can react as fire frequency and severity increases.