Small mammals decline with increasing fire extent in northern Australia: evidence from long-term monitoring in Kakadu National Park Michael J. Lawes A,F , Brett P. Murphy A,B , Alaric Fisher C,D , John C. Z. Woinarski A,C,D , Andrew C. Edwards A,E and Jeremy Russell-Smith A,E A Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, NT 0909, Australia. B Centre of Excellence for Environmental Decisions, School of BioSciences, University of Melbourne, Vic. 3010, Australia. C NERP North Australia Hub, Charles Darwin University, NT 0909, Australia. D Flora and Fauna Division, NT Department of Land Resource Management, PO Box 496, Palmerston, NT 0831, Australia. E Darwin Centre for Bushfire Research, Charles Darwin University, Darwin NT 0909, Australia. F Corresponding author. Email: michael.lawes@cdu.edu.au Abstract. Small mammal (,2 kg) numbers have declined dramatically in northern Australia in recent decades. Fire regimes, characterised by frequent, extensive, late-season wildfires, are implicated in this decline. Here, we compare the effect of fire extent, in conjunction with fire frequency, season and spatial heterogeneity (patchiness) of the burnt area, on mammal declines in Kakadu National Park over a recent decadal period. Fire extent – an index incorporating fire size and fire frequency – was the best predictor of mammal declines, and was superior to the proportion of the surrounding area burnt and fire patchiness. Point-based fire frequency, a commonly used index for characterising fire effects, was a weak predictor of declines. Small-scale burns affected small mammals least of all. Crucially, the most important aspects of fire regimes that are associated with declines are spatial ones; extensive fires (at scales larger than the home ranges of small mammals) are the most detrimental, indicating that small mammals may not easily escape the effects of large and less patchy fires. Notwithstanding considerable management effort, the current fire regime in this large conservation reserve is detrimental to the native mammal fauna, and more targeted management is required to reduce fire size. Additional keywords: Aboriginal burning, fire frequency, fire regime, habitat simplification, patch mosaic burning, predation, tropical savanna. Received 12 September 2014, accepted 7 February 2015, published online 21 May 2015 Introduction Biodiversity is declining severely in tropical areas worldwide, mostly owing to rapid human population growth, habitat loss, hunting, invasive species and inadequate conservation reserves (Mack et al. 2000; Bradshaw et al. 2009). Although the rate of biodiversity decline in tropical Australia may be comparable with that of other tropical areas, the principal factors driving declines elsewhere (broad-scale vegetation loss and hunting) are largely absent here (Woinarski et al. 2001), providing new insights to the natural and non-anthropogenic drivers of mammal declines and their synergies under global change (Brook et al. 2008). In the absence of direct anthropogenic drivers of mammal declines, it is likely that landscape-scale factors are involved. There is increasing evidence that fire is such a factor (Russell-Smith et al. 2009a), but the manner in which fire effects biodiversity declines is poorly known. Here, we seek to better resolve that causality to inform management. Fire is ubiquitous in most Australian landscapes (Murphy et al. 2013) and fire regimes have changed dramatically since European arrival (Ward et al. 2001; Russell-Smith et al. 2003). In some tropical savanna regions of northern Australia, fire regimes are now dominated by large (.1000 km 2 ) contig- uous fires, occurring at short (2–3-year) fire return intervals (Yates et al. 2008). Managing fire for desired environmental outcomes is an important conservation issue in Australia (Russell-Smith et al. 2003; Andersen et al. 2005; Russell- Smith et al. 2007; Di Stefano et al. 2011), requiring a clear understanding of the effects of the timing, frequency and scale of fires on biodiversity (Clarke 2008; Driscoll et al. 2010; Kelly et al. 2011). CSIRO PUBLISHING International Journal of Wildland Fire http://dx.doi.org/10.1071/WF14163 Journal compilation Ó IAWF 2015 www.publish.csiro.au/journals/ijwf