Responses of bats to clear fell harvesting in Sitka Spruce plantations, and implications for wind turbine installation

Abstract

Commercial coniferous plantations are often assumed to be poor habitats for bats. As a result, the impact of forest management practices on bats, such as clear felling, has received little attention, particularly in Europe. However, there is growing evidence from multiple regions that bats do make use of plantation landscapes, and as interest in siting onshore wind turbines in upland conifer plantations grows, there is an urgent need to examine whether felling prior to turbine installation is likely to put foraging bats at risk of collision. In the first study of its kind, we use a “before – after – control – impact” study to explore the short-term impacts of clear fell harvest on bat activity in commercial plantations. Thirty-one mature stands of Sitka Spruce were surveyed using acoustic detectors in three large, upland Sitka Spruce plantations in Britain. Eleven stands were felled between 2013 and 2015, and 26 of the original 31 stands were resurveyed in 2015. The change in total bat activity and species- or genus-specific bat activity was modelled before and after felling occurred at both felled and control stands using generalised linear models. There was no change in overall bat activity at felled sites compared to control sites, but activity ofNyctalusspecies was 23 times higher following felling. TotalPipistrellus spp.activity doubled at felled sites post-harvesting, although this was mainly driven by increased activity at a few felled sites. WhenP. pygmaeusandP. pipistrelluswere considered separately, activity increased slightly but non-significantly. The size of the felled area influenced activity (for bats overall andPipistrellus spp.), with 90% higher activity in smaller felled stands (less than 5ha−1) compared to larger felled stands (greater than 30ha−1). ForP. pipistrellus, activity in felled areas decreased with the duration since harvesting; the greatest activity occurred in stands felled within two months compared to those harvested more than 16months previously. Higher activity for some groups following felling may occur due to the creation of more edge habitat, which is preferred by bothPipistrellusspecies we recorded. An increase in activity following the small-scale felling (‘key-holing’) required for the installation of turbines could put foraging bats at risk from collisions with turbines. Further investigation of the influence of both size of clear fell patch, timing of felling and changes in invertebrate abundance due to felling are required to establish the potential risk of key-holing and turbine installation to foraging bats.