Fire and Snow: Effects of Snowpack Variation and Wildfire on Small Mammal Dynamics in Sub-Alpine Habitats

Montane ecosystems in many parts of the world are threatened by climate change. In Australia, alpine and sub-alpine habitats face warming temperatures, increased risk of wildfire and incursions by invasive species. For small mammals that are active over winter in these habitats, a further risk may arise if the winter snowpack-and the thermally buffered subnivean space that it creates-is impacted. We examine long-term (19-43-year) datasets on three species of small mammal in sub-alpine habitats in Australia to test whether populations decline in years when there is a shallow or transient snowpack, and after wildfire. We anticipated that species would show differential susceptibility to snowpack integrity, with species such as the broad-toothed rat (Mastacomys fuscus), which nests on the soil surface within the subnivean space, likely to be at most risk in years of shallow or transient snow cover. We found that populations of M. fuscus often declined following winters with shallow snow cover, and that the end of snow cover influenced numbers of M. fuscus and a second species, the mainland dusky antechinus (Antechinus mimetes) in the following summer or autumn. Populations of a third study species, the bush rat (Rattus fuscipes), were less affected by snowpack variables. All species declined sharply post-fire; depressions in numbers were most prolonged, and recoveries slowest, for A. mimetes and particularly M. fuscus. Food availability, drought, vegetation cover and differential susceptibility of the study species to predation by the European red fox (Vulpes vulpes) probably contributed to the observed dynamics. We suggest that interactions between snowpack reduction, wildfire and fox predation pose increasing threats to small mammals in Australia's sub-alpine habitats, and call for the development of local management plans for taxa at most risk of collapse.