Insectivorous Bats and Silviculture: Balancing Timber Production and Bat Conservation

Abstract

Forests are one of the most important habitats for insectivorous bats as they offer the potential for both roosting and foraging. We reviewed silvicultural literature from North America, Australia, and Europe and found that diverse research approaches have revealed commonalities in bat responses to forest silviculture. Almost all silvicultural treatments evaluated were compatible with some use by forest bats, though different bat ensembles respond in different ways. Ensemble ecomorphology was a consistent predictor of how bats respond to vegetative clutter and its dynamic changes as forests regenerate and develop a dense structure following harvesting. Sustaining high levels of bat diversity in timber production forests requires a mix of silvicultural treatments and exclusion areas staggered across the landscape, regardless of forest type or geographic region. Use of edge habitats, exclusion areas/set-asides, and riparian corridors for roosting and foraging by bats were consistent themes in the literature reviewed, and these habitat elements need to be considered in forest planning. Densities of hollow or dead trees sufficient to support large populations of roosting bats are unknown and remain a major knowledge gap, but will likely be species contingent. New paradigm shifts in forest management away from the use of even-aged systems to multi-spatial scale retention of mature forest including trees with cavities should be beneficial to bats, which are influenced by landscape-scale management. Such

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

“…The importance of retaining dead trees as roosts for bats, even those that are relatively small (~20 cm DBH), is a further clear management action emerging from our study (see also [5]). Unexpectedly, we also identified ring-barking as an important contributor to the abundance of dead trees in our study area.…”

“…This species is widely distributed across a range of habitats, including semi-cleared farmland in south-eastern Australia. Considerably more data are needed on the patterns of roost selection by different bat species in relation to different management treatments [5]. We are aware of just one other study of bat roosts in relation to thinning, which found a less manoeuvrable edge-space species (Lasiurus borealis) roosting in open conditions created by thinning [29].…”

“…Forest thinning is known to be beneficial for a range of bat species due to increased foraging efficiency by echolocation where clutter levels have been reduced [5,10,23,64]. In contrast, flight activity of Nyctophilus spp.…”

“…Silvicultural thinning of dense secondary forest regrowth reduces tree competition and encourages faster growth of mature, harvestable trees [5]. This is particularly the case when the secondary regrowth that dominates stands post-harvesting comprises trees that are uniform in age and size, creating a high density of stems with few canopy gaps [6].…”

“…Forest thinning reduces clutter levels and so can be beneficial for a range of bat species by increasing echolocation efficiency [5,10,22,23]. Yet, narrow-space species typically have higher activity levels in forests with higher stem densities [24][25][26], highlighting the need for a better understanding of their response to thinning.…”