Contrasting the influence of extent and severity of fire on the occupancy of two marsupial gliders in New South Wales

Context The 2019–2020 Australian wildfires were the largest and most severe fires recorded for south-eastern Australia. Two glider species, the southern greater glider Petauroides volans and the yellow-bellied glider Petaurus australis, were predicted to be severely affected due to widespread habitat loss and vulnerability to the scale and severity of the fires. However, despite similar ecological requirements, differences in species traits were expected to influence their response to fire. Aim Our aim was to investigate the probability of occupancy of each species following the 2019–2020 wildfires in relation to fire severity and spatial extent, and other environmental covariates. We predicted different fire responses for each species, according to their individual species traits. Methods We surveyed for gliders using spotlighting and call-playback, 3 years post-fire across 223 sites, covering the breadth of their ranges in New South Wales. We used occupancy-detection models of each species to compare model fit with four extents (site, 300 m, 500 m and 1000 m) across three severity classes (unburnt, low-moderate and high) while controlling for other factors that are correlated with glider occupancy (e.g. forest disturbance and mean temperatures). Key results Our results reveal strong negative relationships between occupancy of both glider species and high-severity fire. This effect was most significant for the southern greater glider at the largest spatial scale (1000 m), whereas for the yellow-bellied glider the response was more significant at the site level. For both species, low-moderate severity fire at all spatial scales was less predictive than other covariates. Conclusions Southern greater gliders, with their highly specialised diet, small home ranges and limited dispersal capacity, are particularly sensitive to high-severity fire that consumes essential canopy resources at large scales. Yellow-bellied gliders likely have greater resilience to landscape fire due to greater mobility and a broader, more generalised diet. Implications Both glider species are sensitive to forest disturbance, including canopy consuming fire. Low-moderate fire is less disruptive, in line with expectations that both species are resilient to partial canopy scorch, where essential resources remain. Species traits can be used to predict species responses to disturbances beyond the natural disturbance regime.