An experimental test of whether pyrodiversity promotes mammal diversity in a northern Australian savanna

Abstract

The increasing awareness that a fire regime that promotes biodiversity in one system can threaten biodiversity in another has resulted in a shift away from fire management based on vague notions of maximising pyrodiversity, towards determining the optimal fire regime based on the demonstrated requirements of target species. We utilised a long‐running, replicated fire experiment on Melville Island, the largest island off the northern Australian coast, to test the importance of pyrodiversity for native mammals in a northern Australian savanna landscape. We first developed statistical models to determine how native mammal abundance has responded to nine years of experimentally‐manipulated fire frequency. Next, given each species' modelled response to fire frequency, we identified the level of pyrodiversity and optimal mix of fire frequencies that would be expected to maximise mammal diversity and abundance, and minimise extinction risk. This was done for both the entire mammal assemblage and for the mammal species currently declining on Melville Island. Fire frequency was a significant predictor of abundance of the northern brown bandicoot Isoodon macrourus, black‐footed tree‐rat Mesembriomys gouldii, brush‐tailed rabbit‐rat Conilurus penicillatus, grassland melomys Melomys burtoni, pale field‐rat Rattus tunneyi, and mice/dunnarts but not for the common brushtail possum Trichosurus vulpecula. The geometric mean abundance (GMA) of the entire mammal assemblage was positively associated with pyrodiversity, but peaked at an intermediate value. Hence, maximising pyrodiversity would reduce native mammal assemblage GMA below its potential maximum. The fire history for an area that maximised the entire native mammal assemblage GMA consisted of 57% long‐unburnt, 43% triennially burnt and <1% annually burnt. Pyrodiversity did not reduce the extinction risk, nor increase the GMA of declining mammals above that predicted in areas entirely annually or triennially burnt. Synthesis and applications. We demonstrate a useful approach with which to develop fire management strategies based on the demonstrated requirements of target species. By comparing the optimal fire regime identified for the conservation of threatened species and that identified for the entire mammal assemblage, we demonstrate the flexibility of this approach to tailor fire management to address specific management priorities in other fire‐prone environments.

Fire as a key driver of Earth's biodiversity

“…Thus, it is possible to quantify pyrodiversity using standard indices of diversity such as Shannon's index, classically used for species diversity, and thus compare them. For further interpretation, the relative levels of the components need to be examined to explain how each diversity estimate was reached (Davies et al, ). The term pyrodiversity has been used increasingly in the literature, as it is seen to be aligned with the ecological hypothesis that ‘diversity begets diversity’ (Parr & Andersen, ; Bowman et al, ; Kelly & Brotons, ).…”

“…The term pyrodiversity has been used increasingly in the literature, as it is seen to be aligned with the ecological hypothesis that ‘diversity begets diversity’ (Parr & Andersen, ; Bowman et al, ; Kelly & Brotons, ). In practice only one or a few components are assessed on the understanding that they are a surrogate for others or that other components do not vary significantly (Martin & Sapsis, ; Sitters et al, ; Ponisio et al, ; Davies et al, ).…”

More long‐unburnt forest will benefit mammals in Australian sub‐alpine forests and woodlands

“…Older vegetation has been identified as more important for vertebrates than younger fire ages in northern (Davies et al . ), semi‐arid (Kelly et al . ), south‐eastern (Hale et al .…”

“…; Davies et al . ). Nonetheless, studies have identified the disproportionate importance of intermediate and late successional stages for vertebrates and suggested that an even distribution of fire age‐classes may in fact be detrimental for biodiversity conservation (Kelly et al .…”

Better biodiversity accounting is needed to prevent bioperversity and maximize co‐benefits from savanna burning

“…For instance, modeling of mark-recapture data from the Kapalga fire experiment in the Northern Territory (NT) indicated that an increase in fire frequency above once every 5 years increased extinction risk for several small mammals (Dasyurus hallucatus, Trichosurus vulpecula, Isoodon macrourus, and Melomys burtoni; Griffiths, Garnett, & Brook, 2015). In contrast, a fire experiment on Melville Island (elsewhere in the NT) indicated that fire frequency did not influence the abundance of T. vulpecula, and fire had no effect on mammal diversity (Davies et al, 2018). These differences presumably reflect geographic variation among study systems, and caution against generalizations about how small mammals respond to fire.…”