Bushfire and the Malthusian guillotine: survival of small mammals in a refuge in Nadgee Nature Reserve, south-eastern New South Wales

Abstract

Following an intense bushfire in December 1972, small mammals were sampled from November 1973 to June 1976 on a few hectares of unburnt, grassy river flat in the Nadgee Nature Reserve, New South Wales. Hindsight shows the importance of these small unburnt patches as refuges for small mammals. A surprising proportion of wildlife survives a large bushfire, but the post-fire population is in extremis, confronted by famine and exposed to increased predation. All small-mammal species on a forest plot burnt in the ?72 fire disappeared. On the unburnt flat, five species were encountered and continued to survive. There was a common theme to all five populations in the refuge; incessant flux, many births and disappearances, virtually static overall population. The oft-cited ideas of T. Robert Malthus, although seen by some as old-fashioned and wrong when applied to human populations, lend power to our understanding of population events in the small refuge surviving the ?72 fire. The theme is clear: the populations of small mammals on the flat survived, but barely, as the small numbers in each year?s winter show, and it is only by the operation of the ?Malthusian Guillotine? that they are able to do so. The guillotine is an apt metaphor for the survival process; its operation is stark, but it is efficient, and it is mercifully brief. The conservation implications from this study are striking. The most important being the vital role played by refuges following an extensive and intense fire. In an era of global warming and increasing predictions of the likelihood of bushfires rising, such matters will loom even larger.