Date Published: October 4, 2018
Publisher: Public Library of Science
Author(s): Lucinda Kirkpatrick, Jennifer Graham, Sean McGregor, Lynn Munro, Matheus Scoarize, Kirsty Park, Bi-Song Yue.
There is growing recognition that with sympathetic management, plantation forests may contain more biodiversity than previously thought. However, the extent to which they may support bat populations is contentious. Many studies have demonstrated active avoidance of coniferous plantations and attributed this to the lack of available roost sites and low invertebrate density. In contrast, other work, carried out in plantation dominated landscapes have shown that certain bat species are able to exploit these areas. However, the extent to which bats use plantations for roosting and foraging, or simply move through the plantation matrix to access more favourable sites is unclear. We radio tracked female Pipistrellus pygmaeus over two summers to establish the extent to which individual bats use Sitka Spruce plantations in southern Scotland for foraging and roosting and assess the implications for felling operations on bats. Maternity roosts identified (n = 17) were in all in buildings and most were large (> 500 individuals). We found no evidence of bats roosting in mature Sitka Spruce crop trees, although several bats used roosts in old or dead beech and oak trees as an alternative to their main maternity roost. Home ranges were much larger (mean 9.6 ± 3.12 km2) than those reported from other studies (0.6–1.6 km2), and it is likely that roost availability rather than food abundance constrains P. pygmaeus use of Sitka Spruce plantations. At the landscape scale, most individuals selected coniferous habitats over other habitat types, covering large distances to access plantation areas, whilst at a local scale bats used forest tracks to access water, felled stands or patches of broadleaf cover within the plantation. Sitka Spruce plantations support a high abundance of Culicoides impuctatus, the Highland midge which may act as a reliable and plentiful food source for females during lactation, an energetically expensive period. The use of felled stands for foraging by bats has implications for forest management as wind turbines, following small-scale felling operations, are increasingly being installed in plantations; wind turbines have been associated with high bat mortality in some countries. Decisions about siting wind turbines in upland plantations should consider the likelihood of increased bat activity post felling.
In landscapes where we lack a thorough understanding of the interactions and relationships between organisms and their environment, it can be difficult to manage anthropogenic environmental change for the benefit of biodiversity. For example, commercially managed plantation forests, planted with non-native tree species, are a widespread land use type in much of Europe. However, information on the impact that management has on both abiotic and biotic environments, and consequently the organisms which are present, is sparse for many taxa. Plantations are usually large in size, intensively managed and often under surveyed, perhaps due in part to the perception of such habitats as poor for biodiversity. As a result, sufficient information to determine the impact of management on organisms [1,2] or to assess the influence of changing management practices is often lacking. There is growing evidence that changing forest management practices can facilitate social and ecological benefits without impacting economic performance [2–5], thereby providing an opportunity to manage plantations in ways that benefit both biodiversity and commercial interests.
Eleven individual female P. pygmaeus (five in 2014, six in 2015) were radio tracked successfully for between 3 and 6 consecutive calendar days between June and August (Table 1). We collected a total of 9050 telemetry locations, which was reduced to 2371 after subsampling every five-minute intervals.
These results demonstrate that P. pygmaeus makes widespread use of a commercial Sitka Spruce plantation for foraging during an energetically demanding period. The results from the radiotracking support previous work in the same plantation system using a combination of acoustic monitoring and trapping. Using acoustic monitoring, we found higher activity at recently felled stands compared to other stand management types , with activity increasing after felling . Radiotracking confirmed preferential foraging over felled patches for a number of the individuals we tracked. There is a large, breeding population of P. pygmaeus in the study area as we identified several large roosts. While radiotracking is an intensive, costly and potentially invasive process, it provides unparalleled resolution of information about individual behaviour. Combining this with our findings in previous studies, we are able to confirm that P. pygmaeus use of commercial coniferous plantations does indeed seem to coincide with the presence of ephemeral but highly abundant invertebrate prey within an intensively managed, human dominated landscape. Whilst we are unable to estimate what proportion of bats in the 17 colonies located use plantations for foraging, the high density of individuals we recorded in building roosts within plantations suggests that P. pygmaeus use of the plantation matrix may be considerable. Our results differ from other studies carried out in predominantly agricultural environments with a low proportion of coniferous cover, which generally demonstrate avoidance of coniferous plantations [36,54,55]. In contrast, plantation cover dominated land use type in our study area. Although land cover within the plantations was heterogeneous when considering stand density and stand age, we found little evidence that bats preferentially selected broadleaf woodlands and avoided conifer. Habitat preferences were highly variable between individuals but consistent within individuals.