Early responses of bats to alternative silvicultural treatments in wet eucalypt forests of Tasmania.

Abstract

Bats are sensitive to forest management and different silvicultural treatments are likely to impact on species in different ways. We compared the early responses of ultrasonic bat activity to alternative silvicultural treatments in the Warra Long-term Ecological Research Site, in the tall wet eucalypt forests of Tasmania. We sampled 45 sites and recorded 2424 bat passes early in the maternity season of 2008, which provides a base-line for future comparisons. Total bat activity differed little between the silvicultural treatments, but locations within treatments did influence activity. Pre-planned contrasts revealed significantly lower activity at the centre of clear-fell and dispersed retention coupes than control coupes. However, there was no detectable difference between the centre of aggregate retention and control coupes, indicating that this silvicultural treatment appears effective at ameliorating the impacts of logging on bat activity. However, the retained aggregates themselves, both in their centre and along the edge, were seldom used by bats. Activity on the coupe edge was similar to control treatments, and greater than the centre of clear-fell coupes, but not the other treatments. Individual bat taxa responded to treatments consistent with predictions from ecomorphology. We also compared species level activity at paired bat detectors on the ground and in the sub-canopy (20-37 m) along the nearby Tahune airwalk. Activity was 4.5 times greater in the sub-canopy compared to ground detectors set in openings within the understorey. Adjusting the ground activity by this factor in the tall forests of the control coupes suggests that the logging impacts on bat activity are considerably greater than those described above. However, this conclusion makes the assumption that all bats flying in the range of ground-based detectors within logged gaps and adjacent to retained trees are recorded and require no adjustment.