Bat recolonisation of restored jarrah forest in south-western Australia

Joanna Burgar

Keywords: Eucalyptus marginata, dry sclerophyll forest, fauna, echolocation, roost sites

The jarrah (Eucalyptus marginata) forest is part of the internationally recognised biodiversity hotspot of south-western Australia. The northern jarrah forest, approximately 700 000 ha, is subject to multiple uses including timber production, bauxite mining, water supply, recreation and conservation. Alcoa of Australia (hereafter Alcoa) clears, mines and restores approximately 600 ha of forest annually. Alcoa aims to restore a self-sustaining jarrah forest ecosystem. Research suggests that the floristic composition of the jarrah forest tends to be restored, but it is unknown whether the restored forest is habitat for the nine species of insectivorous bats that inhabit the region. Bats are generally considered resilient to human-induced disturbances because of their mobility, ability to exploit anthropogenic structures for roosting and their broad diet. This research project aims to determine if jarrah forest restored after bauxite mining provides habitat for bats.

Works undertaken: Bat activity was surveyed at 64 sites, restored forest of increasing age and reference (mature, unmined) forest (Fig 1), using passive echolocation call detectors. Each site was surveyed for eight nights in spring and summer over two consecutive years. During the first year of the survey, invertebrates were also surveyed at a subset of the sites (n = 24) to determine if there was a difference in invertebrate biomass between restored and reference sites. During the second year of the survey two species of bat, Southern Forest Bat (Vespadelus regulus) and Gould’s Long-eared Bat (Nyctophilus gouldi), were radio-tracked to their diurnal roosts to determine roost site preferences.

Results to date: Bat activity was extremely variable both within sites across nights of sampling and by restoration age. Despite this variation, overall bat activity was significantly higher in reference forest than in restored forest in either year of the survey. In restored forest, overall bat activity was relatively similar regardless of forest age. There was no difference in overall invertebrate biomass between restored and reference sites. The two bat species that were radio-tracked were never found roosting in restored forest. Rather, all diurnal roosts were located within the reference forest, largely in mature jarrah trees.

Figure 1. Restored jarrah forest of increasing age and reference (unmined) forest: a) 0-4 years post restoration; b) 5-9 years; c) 10-14 years; d) >15 years; and e) reference forest.

Lessons learned: Restored jarrah forest provides some habitat for bats, although bat activity was lower in restored than reference forest. Restored forest may provide foraging opportunities, as invertebrate biomass is similar in restored and unmined forest. However, tree hollows take decades to form, so roosting habitat is limited in the restored forest.

 Acknowledgements: This research was possible thanks to ARC Linkage Project LP0882687 between Murdoch University and Alcoa of Australia Limited.

Contact: Joanna Burgar, PhD Candidate, Murdoch University. J.Burgar@murdoch.edu.au Tel: +61 (0)8 9360 6520 http://www.plants.uwa.edu.au/research/ecosystem_restoration