Investigating the congruence between vegetation succession and faunal recolonization in a production landscape: A case study of bats in south-western Australia

Background/Question/Methods

 

Conservation of fauna within production landscapes is imperative to ensure resource extraction occurs sustainably, with no loss of biodiversity. Within the biodiversity hotspot of south-western Australia, Alcoa of Australia mines and restores approximately 600 ha of jarrah (Eucalyptus marginata) forest annually. Restored mine-pits are considered successful based on vegetation succession, while fauna are assumed to passively recolonize. To test this assumption, bat community assemblages were surveyed in restored mine-pits. Bats were chosen as the focal taxa because they require multiple habitats to forage and breed. In addition, there is a paucity of data for jarrah forest bats, despite the presence of two endemic species. Bat echolocation call surveys measuring bat activity were conducted in restored mine-pits of a variety of ages and eucalypt densities, as well as reference, unmined forest. All 64 sites were sampled twice each during maternity and mating seasons across two years between 2010 and 2012 for a total of 512 survey nights. In 2010/2011 invertebrates were sampled from a sub-set of sites to determine prey availability in restored mine-pits and unmined forest. In 2011/2012 two species were radio-tracked to their diurnal roosts to determine roost site requirements.

Results/Conclusions

 

Nine species of bat were recorded within the mined landscape. All species or species groups were recorded in both the restored mine-pits and the unmined forest. However, bat activity was significantly higher in unmined forest than the restored mine-pits, regardless of eucalypt age or density. Overall bat activity was lower in younger restored mine-pits than older sites and as restored forest aged, bat activity was highest in the least dense eucalypt stands. Invertebrate biomass was greater in unmined forest than restored mine-pits of any age. All bats used diurnal roosts, typically mature trees, within unmined forest, not one was observed roosting in restored mine-pits. These results suggest that although some restored mine-pits may be on a desired trajectory of vegetation succession for tree stands, they are not yet suitable habitat for bats. Structurally, the oldest restored forest is still dissimilar to that of unmined forest, and tree hollows, important for roosting, take many decades to form so will be lacking in restoration for some time. Plant community assemblage may be a better benchmark of restoration success for faunal communities than the current focus on tree densities because it will better reflect congruence in habitat structure with reference, unmined forest.