Koalas prefer blue gum over three other plantation species

Context Commercial forestry plantations can provide shelter, food and connectivity among native forest remnants in landscapes with extensive habitat clearance. In their southern range, koalas (Phascolarctos cinereus) have responded favourably to the establishment of blue gum (Eucalyptus globulus) plantations, but their use of other plantation species remains undocumented. Understanding this is critical for the conservation of a genetically distinct koala population in the heavily modified Strzelecki Ranges region of Victoria. Aim We aimed to determine the relative density of koalas in four plantation species compared with remnant native forest in the Strzelecki Ranges, Victoria. Methods Sites (N = 59) were stratified across six forest types, including four plantation species (blue gum, Eucalyptus globulus subsp. globulus; shining gum, E. nitens; mountain ash, E. regnans; and radiata pine, Pinus radiata) and two native forest classifications (high or low suitability for koalas). Sites were each surveyed for koalas once, using a drone mounted with a thermal camera and spotlight (DJI Matrice 300 RTK) that was flown in manual mode and systematically searched each site. Koalas were detected in real time by the pilot. Survey effort was determined from the area of canopy and subcanopy surveyed, which ranged from 2.2 to 14.6 ha per site. A generalised linear model with negative binomial distribution was used to determine the influence of forest type on relative koala density. Key results Relative koala density was highest in blue gum plantations, with 0.28 koalas ha−1 (95% CI: 0.13–0.61) and high-suitability native forest, with 0.38 koalas ha−1 (95% CI: 0.18–0.82). Other plantation types had relative densities of fewer than 0.1 koalas ha−1 on average. Large confidence intervals for all forest types suggested high variability or uncertainty. Conclusions Blue gum was the only plantation species favoured by koalas; however, it is grown in only a small proportion (<5%) of plantations in the region. Implications Most of the plantation estate is not habitat preferred by koalas. Conserving koalas in this region therefore relies on maintaining and increasing the extent, connectivity and quality of native forest. Further study is needed to improve our understanding of koala tree preferences and the influence of landscape characteristics on use of different forest types.