Long term monitoring reveals the importance of large, long unburnt areas and smaller fires in moderating mammal declines in fire-prone savanna of northern Australia.
Abstract
Biodiversity loss is often attributable to multiple interacting pressures that are moderated across environmental gradients. These processes contribute to complex responses that are challenging to interpret and understand. Well-designed and well-implemented monitoring can play a vital role in this but is rarely undertaken. Mounting evidence suggests that current fire regimes across Savanna ecosystems have contributed to the decline of a range of biota. Hence, contemporary fire regimes are at odds with conservation goals. Using an extensive spatiotemporal monitoring dataset from three large National Parks in northern Australia, we applied generalised linear mixed models to examine: (1) trends in mammal richness and abundance through time and variation across environmental gradients such as productivity or landscape position (e.g. terrain ruggedness); and (2) how fire, a potential driver, is moderated by environmental gradients. Across 24 years, major declines in mammal richness and abundance were observed with greater reductions in less rugged and less mesic habitats. Patterns of decline were related to multiple aspects of fire regimes, but not changes in vegetation structure and composition, or cane toads, Rhinella marina, arrival and concomitant poisoning of predatory animals during consumption. More pronounced declines occurred in sites that were exposed to larger fires, had less long unburnt (>5 years without fire) vegetation and were more distant from large, long unburnt patches. Relationships between mammal persistence and fire varied among vegetation communities, with the strongest fire effects observed in lowland woodland-drier with few barriers to fire spread-where the availability of long unburnt areas moderated declines more than in other vegetation communities. Synthesis and applications. Current fire regimes are contributing to mammal declines in northern Australian Savanna. Collectively, our results highlight: (1) the value of long term monitoring, and importance of considering landscape position when assessing faunal responses to landscape-level perturbations like fire; (2) that significant improvements in fire regimes are required to ameliorate mammal declines; and (3) the need to shift management focus from retaining small, short-lived unburnt patches toward preserving relatively large contiguous areas of long unburnt habitat, particularly in less rugged lowland and sandstone woodlands.