Small mammal diversity is higher in infrequently compared with frequently burnt rainforest-savanna mosaics in the north Kimberley, Australia

Context: Populations of native mammals are declining at an alarming rate in many parts of tropical northern Australia. Fire regimes are considered a contributing factor, but this hypothesis is difficult to test because of the ubiquity of fire.

Aims: This preliminary study investigated relative abundance and richness of small mammals on a gradient of fire regimes in the Uunguu Indigenous Protected Area (north Kimberley, Australia).

Methods: Species were sampled using 40 unbaited camera traps, positioned for a year on 20 transects crossing the rainforest–savanna boundary at locations with comparable environment and geology but varying fire history. The relative importance of the factors ‘fire frequency’, ‘late dry season fire frequency’, ‘time since burnt’ and ‘vegetation type’ as predictors of the number of small mammal species and detections was tested using Spatial Generalised Linear Mixed Models to account for spatial autocorrelation.

Key results: Nine species of small mammals were observed. Mammals were more abundant and diverse in locations with low overall fire frequency, which was a better predictor than late dry season fire frequency or time since burnt. The model including fire frequency and vegetation explained the highest proportion of total variation in mammal diversity (R² = 42.0%), with most of this variation explained by fire frequency alone (R² = 40.5%). The best model for number of detections (R² = 20.9%) included both factors.

Conclusions: In the north Kimberley, small mammals are likely to be more abundant and diverse in areas with low fire frequency.

Implications: This natural experiment supports the theory that frequent fires are contributing to the decline of small mammals observed across northern Australia.