Passive acoustics and sound recognition provide new insights on status and resilience of an iconic endangered marsupial (koala Phascolarctos cinereus) to timber harvesting.

Bradley S Law,Paul Roe,Leroy Gonsalves,Anthony Truskinger,Traecey Brassil,Anna Mcconville,Mathew S Crowther

doi:10.1371/journal.pone.0205075

Abstract

Retention forestry aims to mitigate impacts of native forestry on biodiversity, but data are limited on its effectiveness for threatened species. We used acoustics to investigate the resilience of a folivorous marsupial, the koala Phascolarctos cinereus, to timber harvesting where a key mitigation practice is landscape exclusion of harvesting. We deployed acoustic recorders at 171 sites to record male bellows (~14,640 hours) for use in occupancy modelling and for comparisons of bellow rate (bellows night-1). Surveys targeted modelled medium-high quality habitat, with sites stratified by time since logging and logging intensity, including old growth as a reference. After scanning recordings with software to identify koala bellows, we found a high probability of detection (~0.45 per night), but this varied with minimum temperature and recorder type. Naïve occupancy was ~ 64% across a broad range of forests, which was at least five times more than expected based on previous surveys using alternative methods. After accounting for imperfect detection, probability of occupancy was influenced by elevation (-ve), cover of important browse trees (+ve), landscape NDVI (+ve) and extent of recent wildfire (-ve, but minor effect). Elevation was the most influential variable, though the relationship was non-linear and low occupancy was most common at tableland elevations (> 1000 m). Neither occupancy nor bellow rate were influenced by timber harvesting intensity, time since harvesting or local landscape extent of harvesting or old growth. Extrapolation of occupancy across modelled habitat indicates that the hinterland forests of north-east NSW support a widespread, though likely low density koala population that is considerably larger than previously estimated. Retention forestry has a significant role to play in mitigating harvesting impacts on biodiversity, including for forest specialists, but localised studies are needed to optimise prescriptions for koalas.

Highlights

Multiple use native forests produce pulp, timber, bioenergy and a range of other natural products
We found minimum nightly temperature had the greatest influence on detection probability and this was Acoustics and response to timber harvesting by koalas correlated with month of survey during the breeding season, with lower detectability in December than September
Koala high-use exclusion areas represent one method of retaining patches of large browse trees where an accumulation of koala scats had been identified prior to harvest, but we found occupancy was no greater in these areas than other treatments, and bellow rate was greater, the difference was not significant

Summary

Introduction

Multiple use native forests produce pulp, timber, bioenergy and a range of other natural products. One model of forest management, referred to as ‘retention forestry’, aims to balance the goals of wood production and biodiversity conservation [4, 5]. Retention forestry retains single trees and/or intact forest patches at the time of harvest with the aim of conserving forest biodiversity and sustaining ecological functions [5]. A recent meta-analysis identified retention forestry as the most effective forest management approach in timber production forests for minimising species loss [6]. The area excluded from harvesting ranges from

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