Biodiversity monitoring is recognised as a key action for ecologically sustainable land use, but there are few examples of landscape programmes. We outline the first five years of biodiversity monitoring focusing on insectivorous bats in low rainfall, multiple-use forests and woodlands of the Pilliga, Australia. Using ultrasonic sampling over multiple nights, both on- and off-tracks, we identify annual trends in bat activity and occupancy and environmental covariates. Trends differed depending on whether occupancy or bat activity was the response variable. Site occupancy was almost 100% and remained stable and/or did not decline for most species nor diversity over the monitoring period, suggesting little variation in bat populations. In comparison, total activity was initially very high (567 passes night(-1) on-track) and then declined by up to 40% in the following three years, but then fully recovered in the fifth year. This general pattern was evident both on- and off-tracks for most taxa, though activity was three times greater on- than off-track, highlighting the importance of these distinct habitat features for bats. Multivariate state-space (MARSS) models predicted, unexpectedly, that high winter rainfall prior to our surveys was negatively related to activity for many taxa. In contrast, disturbance from timber harvesting or fire had weak or no identifiable effects on trends in activity for most taxa. One exception was Chalinolobus picatus (threatened), whose occupancy off-tracks was negatively related to the extent of recent (<5 years) fire and to harvesting, though at the landscape scale, occupancy remained stable. This result, together with patterns for other bat taxa, suggests that disturbance effects were short-lived/dispersed and/or environmental mitigations were effective at maintaining bat populations at a landscape level. Annual monitoring highlighted annual variation in activity and its implications when setting a baseline for monitoring. We also discuss modifications to future monitoring effort, based on the existing five years of data.

Management of forest regrowth is a key issue globally, particularly where it occurs as high densities of small sized stems and where there is little to no self-thinning. Thinning can reduce stem density to accelerate tree growth and potentially restore forest-structural complexity. Yet, in some forest types, it remains unclear how biodiversity responds to thinning, especially over longer periods. White cypress pine Callitris glaucophylla is geographically widespread in Australia and has history of silvicultural thinning in parts of its distribution. We used a chronosequence approach to assess the short- and longer-term responses of multiple taxa (bats, birds, invertebrates, reptiles, non"volant mammals, and plants) to thinning of C. glaucophylla in the dry Pilliga forests of New South Wales. We recorded data from a total of 227 taxa. The short (< 8 years)- and longer-term (> 20 years) responses to thinning of C. glaucophylla regrowth were mostly positive or neutral for the taxa considered. Bat activity and diversity were comparable to levels in long-undisturbed reference forest, though this was influenced by time since thinning. Reptile diversity and abundance was positively associated with thinning at an intermediate time since thinning (8-20 years), with both metrics greater than unthinned regrowth and long-undisturbed reference forest. Bird diversity was greater in recent and old thinning treatments when compared to unthinned forest regrowth, although species composition was not affected by thinning. Though thinning did not affect volant invertebrate biomass, it was associated with a relatively more even distribution among size classes > 8 years post-thinning, and a greater representation of beetles to overall insect biomass. The activity, diversity and composition of non-volant mammals did not differ among treatments, nor did understorey plant diversity or composition. Combining these multiple taxa into a composite 'biodiversity' index demonstrated a 16-22% increase with thinning relative to index values in long-undisturbed reference forests. Overall these results indicate that thinning has neutral to positive effects on biodiversity, but responses are species-specific and likely to be dependent on forest-type and the broader landscape of a site. Given unthinned forest represented habitat of similar value to thinned forest for some taxa, we recommend that that regrowth patches of varying size are retained across the landscape to provide a mosaic forest structure suitable for a diverse suite of flora and fauna.

Forest thinning is a widely used silvicultural practice that has potential to provide benefits for biodiversity, but there is little direct evidence for this, particularly for regrowth in low rainfall forests and woodlands. This study examined the long-term effects of thinning on structural attributes of white cypress pine (Callitris glaucophylla) in the Pilliga forests of eastern Australia. A chronosequence approach was used which included six replicates of five forest management treatments; Unthinned (> 80 years) with high density regrowth; Recent thinning (< 8 years); Intermediate thinning (8-20 years); Old thinning (21-40 years); Long undisturbed (> 80 years) with large Callitris and Eucalyptus trees present. Thinning reduced the dominance of species that form dense single aged stands (Allocasuarina luehmarinii and Callitris spp.). Following thinning there was a similar to 4-fold reduction in small stems (< 10 cm, diameter breast height (DBH)); 6030 stems ha(-1) (Unthinned) compared to 1583 stems ha-1 (Recently thinned). The reduction in small stemmed vegetation was associated with lower cover in both the mid-storey (2-6 m) and sub-canopy (6-14 m) which persisted for 21-40 years while the long undisturbed treatment had mid-storey densities which were similar to the unthinned treatment. Density of medium-sized Eucalyptus spp. (10-30 cm DBH) was highest (> 90 trees ha-1) where thinning had occurred (recent, intermediate and old thinning treatments) or where stem density of Allocasuarina and Callitris regrowth was low (long undisturbed), suggesting both these species competitively exclude recruitment of Eucalyptus spp.. The post thinning reduction in woody vegetation was accompanied by an initial increase in the volume of downed coarse woody debris (DCWD), which was long lasting (21-40 years) and four to eight times greater than in long un-disturbed sites, with greatest mean hollow diameter occurring in the old thinning treatment. Commercial thinning, in which some residue is removed from sites, still supported up to four times the DCWD volume as the long undisturbed treatment. There was a trend for a negative effect of thinning on the density of dead trees, but no effect on density of hollow-bearing trees and large trees (> 50 cm DBH). Overall, our results indicate thinning had a mixed effect on key structural attributes that contribute to habitat structural complexity, indicating a need to record the direct responses of biodiversity.

Summary Over half of the world's forests are secondary regrowth and support considerable biodiversity. Thinning of these forests is a widespread management practice that can affect forest species, including echolocating bats and their prey. We compared total activity of 11 bat taxa, foraging activity of six bat guilds and biomass of 11 insect orders across four forest thinning categories in managed remnant eucalypt forests in south‐eastern Australia: unthinned regrowth, forest thinned recently (0–4 years) and in the medium term (5–10 years) and reference (mature open forest). Thinning had been carried out at large (˜350 ha) spatial scales. Total bat activity was 60% less and foraging activity was 80% less in unthinned regrowth, compared to reference sites, but activity levels were similar among thinned and reference sites. Insect biomass was greatest in unthinned sites, and while bat activity was related to prey biomass, this relationship was weak in unthinned sites. Together, this suggests that forest structure was more important than prey availability or time since thinning in influencing bat activity patterns. Synthesizing our findings with the broader literature on bats and thinning, we found support for a clutter threshold of 1100 stems ha−1, above which bat activity was markedly lower, across two continents (the USA and Australia) and four broad vegetation types (eucalypt, conifer, deciduous and mixed forests). While elsewhere bats with adaptive traits for open habitats generally respond positively to thinning, in our study, species with traits consistent with clutter tolerance (high call frequency and low wing aspect ratio) had lowest activity levels (up to 22 times) in unthinned regrowth compared to all other forest types. Synthesis and applications. Widespread dense regrowth forest can restrict movement and foraging of bats, even those adapted to clutter. We recommend thinning dense regrowth or plantations to below 1100 stems ha−1 when targeting bat foraging habitat, but effects of thinning on roost habitat and other forest biota require further investigation.

Landscape-scale monitoring is a key approach for assessing changes in indicators. However, great care needs to be taken to collect rigorous data and avoid wasting resources in long-term programmes. Insect-eating bats are diverse, functionally important and are often proposed as indicator species of environmental health. We used acoustic (ultrasonic) data from pilot bat surveys undertaken in forests and woodlands to optimize sampling effort to produce precise estimates of bat activity and occupancy. We also carried out simulations to evaluate the statistical power of different sampling designs to detect changes in activity and occupancy levels of individual bat species. There was little gain in precision for estimates of bat activity by sampling beyond five to six detector nights. To ensure spatial heterogeneity was sampled around a monitoring point, three detectors for two nights or two detectors for three nights would be required. This level of sampling was also sufficient to be 90% certain of recording occupancy for 11 of 12 taxa. Power simulations revealed that a sampling design using two detectors per monitoring point for two nights could detect a 30% decline within 10 years with 90% power for all species, except the white-striped free tail bat (Tadarida australis), using either changes in activity levels or occupancy. However, fewer years were required when using occupancy. Setting detectors either on-flyways or off-flyways contributed only minor differences to the time taken to reach 90% power for both occupancy and activity levels, though sampling both locations has major implications for interpreting trends in bats. We suggest that bat activity levels are more sensitive for detecting change than occupancy because one pass or 1000 passes can be recorded per night by an acoustic detector, and this is not differentiated by occupancy. Bats can be monitored cost-effectively and should be included in monitoring programmes.

Riparian zones provide significant habitat for microbats. In forests subject to logging, buffers are normally retained along stream-beds to maintain water quality and protect riparian vegetation and its associated fauna. We sampled bat activity as part of a broader program to assess biodiversity and to provide a scientific basis for determining buffer widths around ephemeral streams in the Pilliga State forests of north-west New South Wales. Anabat detectors recorded bat activity over two consecutive nights in one season at each of three dry stream-bed sizes (small, medium and large), clustered into five different locations (replicates). Anabat detectors were placed at varying distances perpendicular from the dry, stream-bed centre of ephemeral streams (0 m, 50 m, 100 m, 200 m). To assess the influence on bat activity of the flyway per se versus the riparian zone, one cluster of sites represented a control or reference that comprised dirt roads of three equivalent widths. Over the course of the study 22,967 bat calls were recorded from 15 species. A multivariate analysis of species composition indicated that there was no distinct bat assemblage characteristic of the riparian zone. Overall, bat activity was not influenced by stream-bed size or the perpendicular distance from the stream-bed. However, there was a significant interaction between distance and stream-bed size, with large stream-beds supporting three times more activity over the channels than adjacent forest and woodland. Similarly for reference sites, there was more activity directly over the road than adjacent woodland. The response of individual species to flyways on the different-sized stream-beds varied generally in accordance with predictions based on their ecomorphology and echolocation call type. We conclude that large flyways have the most biological importance to the activity of a range of bat species and that, in conjunction with studies on other components of biodiversity, the riparian zone rarely extends beyond the stream-bed channel in the Pilliga forests.