Where There's Smoke There's Fire: How Mixed Severity Wildfires Affect a Community of Wildlife Species

Kylie N. Denny

doi:10.7273/000007038

Wildfire management must adjust to rapidly changing wildfire regimes (e.g., increasing frequency and severity) by prioritizing reducing the risk of large, high severity wildfires. Consequently, fire-prone systems are beginning to deviate from naturally heterogeneous landscapes that have been historically maintained by mixed-severity wildfires. Uncertainty remains regarding how wildlife communities respond to two components of wildfire regimes, fire severity (i.e., the amount of post-fire change in vegetation) and fire heterogeneity (i.e., variation in fire severity). It is critical to understand how wildlife communities are responding to post-disturbance environments to effectively balance wildlife and wildfire management. Thus, we evaluated how fire severity (at a landscape and plot level) and fire heterogeneity influenced wildlife occupancy across four recent (4-5 years old) mixed-severity wildfires in the Colville National Forest in northeastern Washington. In the summers of 2019-2020, we distributed 207 remote cameras across 4 fire severity categories (unchanged, low, moderate, high). We used camera images from 13 species to conduct single-season single-species occupancy models, including for black bears (Ursus americanus), bobcats (Lynx rufus), cougars (Puma concolor), coyotes (Canis latrans), gray wolves (Canis lupus), Rocky Mountain elk (Cervus canadensis), moose (Alces alces), mule deer (Odocoileus hemionus), white-tailed deer (Odocoileus virginianus), red squirrels (Tamiasciurus hudsonicus), snowshoe hares (Lepus americanus), striped skunks (Mephitis mephitis), and wild turkeys (Meleagris gallopavo). We included in our models a suite of environmental and detection covariates and selected top models based on the Akaike Information Criterion corrected for small sample size (AICc). Landscape level fire severity, fire heterogeneity, and level fire severity were included in the top model for 10 of 13 species with 85% confidence intervals that did not overlap 0. Most species responded negatively or curvilinearly to fire severity, with lowest probabilities of use in high fire severity and a mixture of probabilities of use in low and moderate severities. Our results suggests that required resources (i.e. cover, food, thermal protection) likely vary among patches of differing fire severities. Further, several species responded to variation in fire severity by using a broad range of fire severities or by responding positively to increasing fire heterogeneity. We speculate that the responses to fire severity and heterogeneity are strongly influenced by how much time has passed since the fires burned and patterns of vegetation regeneration in burned areas. Our results provide both complementary and contradictory evidence for patterns of wildlife post-fire use observed in other systems. Nevertheless, we provide additional context for how wildlife communities respond to two poorly understood components of wildfire regimes, fire severity and heterogeneity, in an era of rapid environmental change.

Where There's Smoke There's Fire: How Mixed Severity Wildfires Affect a Community of Wildlife Species

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