Response of an arboreal species to plantation harvest

Abstract

Plantation forests are increasing worldwide and generally have lower biodiversity value than surrounding native vegetation. However, when established on previously cleared land, they can provide important habitat for some wildlife species and have positive conservation outcomes. In southern Australia, the establishment of southern blue gum (Eucalyptus globulus) plantations on cleared land has expanded the area of koala (Phascolarctos cinereus) habitat; however, koalas are at risk of injury, death and displacement when plantations are harvested. Consequently, an understanding of the response of koalas to harvesting is vital for developing management strategies that allow for plantation harvest while also improving welfare outcomes for koalas. We used GPS tracking and a before-after-control-impact (BACI) design to investigate the impact of blue gum plantation harvest on koala survival, body mass, reproduction, and movements. A total of 44 koalas (17 males, 27 females) from two plantations (one harvested, one unharvested) were monitored for 8 months encompassing before (5 weeks), during (11.5 weeks) and after (15.5 weeks) harvest. Survival was high with only two koalas (harvested plantation) dying of unknown causes but neither considered to be a direct result of harvesting. Harvesting did not have any detectable impact on body mass and pouch young production and only a minor effect on the amount of time koalas spent moving. By the end of the study period, 79% of the koalas originally living in the harvested plantation had moved to the surrounding plantations, while the remainder stayed within the harvested area in unharvested trees. In the unharvested plantation, 18% moved out and 82% remained. We attribute the high survival during harvest to active searching by koala ‘spotters’ ahead of harvesting machinery and subsequent retention of each koala’s tree and the surrounding eight trees. We suggest that the proximity of the harvested plantation to adjacent plantations facilitated safe dispersal of koalas out of the plantation, increasing the probability of survival and reducing the energy and movement distances. Our findings suggest that the plantation harvesting can result in minimal impact on resident koalas but that the influence of landscape context around harvested plantations should be the subject of future research.