E&E PhD Exit Seminar: Investigating the effects of bushfires on koalas and their habitat

Bushfires are a major disturbance process in the Australian landscape, affecting our native wildlife and their habitat. The dry sclerophyll forests of south-eastern Australia are one of the most fire-prone regions in the world and are dominated by tree species from the Eucalyptus genus. Eucalypt species are well-adapted to tolerate fire, with species from this genus known to be some of the most prolific epicormic resprouters, producing epicormic growth rapidly after fire to aid recovery. These eucalypt forests also home to several arboreal marsupial folivore species, including the iconic koala (Phascolarctos cinereus), that utilise these forests for both food and shelter. Like other plant material, eucalypt leaves are often low in essential nutrients (i.e., nitrogen) and high in herbivore-deterrent plant secondary metabolites (PSMs), which strongly influence the feeding behaviour of these animals.

The 2019-2020 megafires that burned on the eastern side of Australia were unprecedented in both scale and intensity, burning large areas of important habitat that were used by many of our native fauna. The koala was one of many animals affected by these fires, with their slow and arboreal nature affecting their ability to not only escape fires, but also survive after fire, following the destruction of essential habitat. My research observes the effect of these megafires on a population of koalas in the New South Wales Southern Tablelands and how fire impacted the nutritional quality of their habitat. I looked at both koala health and their movements in a burnt and unburnt landscapes after fire and compared that to rehabilitated koalas that came into care after the fires and were later released. I also observed the nutritional changes in these landscapes over time, quantifying the chemical composition of epicormic growth, and how it compares to the quality of mature growth, to gain a better understanding of the longer-term effects of fire on these important habitats.

With this research, I found that koalas can live in and form home ranges in burnt areas, with movements and home ranges similar between the burnt and unburnt, and rehabilitated koalas having significantly larger home ranges. Furthermore, I also observed that koalas living in burnt areas were in similar health and body condition, suggesting that, with sufficient browse and nutrition, koalas are capable of utilising burnt landscapes. For the nutritional aspect, while epicormic growth had higher concentrations of nitrogen, it contained higher concentrations of some PSMs, suggesting there are trade-offs for the animal when consuming this type of foliage. Interestingly, the composition of this growth and mature foliage varied over time in our study, showing that foliage may be more or less optimal at different times, which may influence how koalas use a landscape.

Despite the regular occurrence of fire in Australia, this is the first research that has observed the nutritional quality of epicormic growth and how it changes over time. It is also the first to document the health and behaviour of koalas in this region and provides valuable insight into how koalas may use burnt landscapes after a major fire event.