Does Thinning Homogenous and Dense Regrowth Benefit Bats? Radio-Tracking, Ultrasonic Detection and Trapping

Abstract

Abstract:Renewal ecology promotes the creation and enhancement of landscapes that support biodiversity and ecosystem services for humans. Silvicultural thinning of forest regrowth to reduce tree competition represents a form of active management that may also benefit biodiversity, especially where secondary regrowth dominates. However, ecological responses to thinning can be complex, particularly for insectivorous bats whose ecomorphology is often related to vegetation structure. Furthermore, thinning may affect multiple aspects of bat ecology (i.e., roosting and foraging). We assessed this in dense white cypress regrowth in the Pilliga forests of New South Wales, Australia, where recent experimental thinning created thinned stands (4 × 12 ha) surrounded by unthinned regrowth. We contrasted flight activity and roost selection of three narrow-space species with differing conservation statuses (Nyctophilus corbeni, N. gouldi and N. geoffroyi), plus one edge-space species (Vespadelus vulturnus). Radio-tracking over two maternity seasons revealed a preference by all species for roosting in dead trees that were slightly larger than the mean for available dead trees in the vicinity. Although all tagged bats were caught in thinned patches, only 6% of roosts were located there. In contrast, ultrasonic detectors recorded significantly greater activity for V. vulturnus (p = 0.05) in thinned than unthinned patches and no treatment difference for Nyctophilus spp. Systematic trapping using acoustic lures found a higher trap rate for N. gouldi in unthinned than thinned treatments, but no treatment effect for N. corbeni, N. geoffroyi and V. vulturnus. Our results reveal differential use of forest treatments by multiple species, emphasising the value of heterogeneous landscapes supporting thinned and unthinned patches of dense regrowth.

Landscape monitoring reveals initial trends in occupancy and activity of bats in multiple‐use forests

“…Detection covariates: temp = minimum daily temperature; rain = total daily rainfall. Occupancy covariates: rain_apr-sep = winter rainfall; ndvi_apr-sep = mean winter NDVI; Harvest_pre5 = extent of recent (<5 years) harvesting; Harvest_5_15 = extent of intermediate (5 Nyctophilus spp., activity immediately increased fourfold (Law et al 2018a). The response by V. vulturnus may be short-lived (see also Gonsalves et al 2018), as monitoring reported here found that this species was negatively associated off-track with the extent of intermediate time since harvesting (5-15 years), but positively associated with the extent of older (5-15 years) fires.…”

“…Two of the species are relatively common (N. gouldi, N. geoffroyi), but the third is listed nationally under threatened species legislation as Vulnerable (N. corbeni). Rather than attempting to monitor these species with an expensive trapping programme, targeted research has aimed to better understand habitat use and resource requirements (Law et al 2016) and response to disturbances such as thinning (Law et al 2018a) and fire (authors, unpubl. data) as the primary means of informing management.…”

“…Moreover, experimental thinning of dense regrowth in the Pilliga found that V. vulturnus , but not Nyctophilus spp., activity immediately increased four‐fold (Law et al . 2018a). The response by V. vulturnus may be short‐lived (see also Gonsalves et al .…”

“…2016) and response to disturbances such as thinning (Law et al . 2018a) and fire (authors, unpubl. data) as the primary means of informing management.…”

Microbat responses to forest decline

“…; Law et al . ). By contrast, declining forest will have more transparent canopy, more bare dead branches and a greater incidence of gaps.…”