Responses of small mammals to prescribed low-intensity fire: Genetic insights from a northern Australian fire experiment

Prescribed fire is widely used for habitat management in savannas, with biodiversity conservation as a specific objective. However, it is rarely underpinned by an understanding of the mechanisms determining species' responses to fire and persistence in fire-prone environments. We conducted a fire experiment in a mesic northern Australian savanna to investigate the demographic and genetic responses of three small mammal species to fire in areas with different fire frequencies. Live-trapping surveys were conducted before the experimental burns (pre-fire), six-weeks post-fire, and one-year post-fire. For each species, we tested for changes in the number of individuals, capture rates, apparent survival and temporary emigration, genetic diversity, genetic structure, and spatial patterns of relatedness.

More northern brown bandicoots (Isoodon macrourus) and northern brushtail possums (Trichosurus vulpecula arnhemensis) were captured in high fire frequency plots, whereas more black-footed tree-rats (Mesembriomys gouldii melvillensis) were captured in low fire frequency plots. There was no direct effect of the low-intensity fire event on any demographic or genetic metric for any species. However, there was evidence of species-specific dispersal dynamics, with genetically related northern brown bandicoots more dispersed than the other species, especially six-weeks post-fire. Genetically related northern brushtail possums and black-footed tree-rats mostly occupied the same plots with no effect of fire.

This research shows that low intensity fire events within early dry season fire management programs in northern Australia have minimal direct impact on populations of these small mammal species but heterogeneity in long-term fire frequency is important for providing habitat for diverse species. However, infrequently burnt habitat is increasingly rare but important for some declining species like the black-footed tree-rat. We therefore recommend strategic long-term fire management that considers the habitat characteristics required for co-occurring species with distinct habitat requirements and life-histories.