Effects of large-scale high-severity fire on occupancy and abundances of an invasive large mammal in south-eastern Australia

Context. Despite large mammals being an important component of many ecosystems, there is little information on the impacts of fire on large mammal populations. Aims. We evaluated the effects of the large-scale high-severity 'Black Saturday' fires of 7 February 2009 on occupancy and abundances of an invasive large mammal, the sambar deer (Cervus unicolor), in south-eastern Australia. Methods. The effects of the Black Saturday fires on the abundance of sambar deer were assessed using repeated annual counts of faecal pellets during 2007-11 in Kinglake National Park, which was burnt, and in Mount Buffalo National Park, which was not burnt. Pre-fire occupancy was modelled from data collected at 80 4-km(2) cells using three survey methods. The same survey methods were used at 15 burnt (n = 9 sampled pre-fire) and 15 unburnt (n = 5 sampled pre-fire) cells 16-24 months after Black Saturday. Because multiple surveys were performed in each cell, we used a Bayesian state-space site-occupancy model to partition changes in the probability of occupancy from changes in the probability of detection. Key results. Counts of sambar deer pellets increased linearly during 2007-11 in the unburnt Mount Buffalo National Park. Pellet counts also increased linearly in Kinglake National Park from 2007 to 2008, and then decreased (to zero) following Black Saturday; pellet counts increased again in 2010 and 2011. Sambar deer occupancy was weakly reduced (from 0.99 to 0.88) in burnt cells 16-24 months after Black Saturday, but was little changed in unburnt cells (from 0.99 to 0.98). Conclusions. We conclude that the abundance of sambar deer was substantially reduced by the large-scale high-severity Black Saturday fires, but that most burnt habitat was reoccupied 16-24 months later. Implications. There is concern about the negative impacts of invasive sambar deer on native biodiversity, particularly immediately post-fire. Our study suggests that it takes at least 8 months before sambar deer recolonise areas burnt by a large-scale high-severity fire; however, a risk-averse approach would be to act (e.g. by erecting fences or culling) sooner than that.