Data from: Bat communities respond positively to large-scale thinning of forest regrowth

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.