Quantifying the impacts of bushfire on populations of wild koalas (Phascolarctos cinereus): Insights from the 2019/20 fire season

The impact of bushfire events on wild Koala (Phascolarctos cinereus) populations is poorly understood. Following the 2019/2020 bushfire season in eastern Australia, we resurveyed 123 field sites for which contemporaneous (current koala generation) pre-fire survey data were available. Field sites were distributed across six fire grounds between Foster and Ballina on the north coast of New South Wales. At these sites, pre-fire naive occupancy levels by koalas ranged from 25% to 71% of the sampled habitat, while post-fire naive occupancy levels ranged from 0% to 47%. The median reduction in the naive occupancy rate by koalas when considered across all six fire grounds was 71% when standardized against pre-fire occupancy levels. Field data provided strong corroboration between site-based, post-fire foliage canopy cover estimates and modelled Google Earth Engine Burnt Area Map (GEEBAM) fire-severity categories. In terms of GEEBAM fire-severity categories, koala survival was five times more likely in areas where forest canopies were modelled as Unburnt or Partially burnt, compared to areas where forest canopies were Fully burnt. The capacity of bushfire-affected koala populations to recover from the 2019/20 fire season will be conditional upon size of the original population in each fire-affected area, the enactment and implementation of supportive, recovery-themed management regimes, future inter-fire intervals and associated intensities. Management actions necessary to assist recovery actions are discussed.

Automated summary

The study investigated the impact of the 2019/2020 bushfire season on wild Koala populations in eastern Australia. It found that bushfires had a severe impact on Koala populations, especially in areas where forest canopies were fully burnt, leading to a significant reduction in Koala survival. The recovery capacity of Koala populations post-fire will depend on the size of the original population and the implementation of recovery-focused management actions.