Birds and butterflies at the forest-farmland interface

Land-use change is one of the greatest threats to biodiversity. Through intensification of land-use, the agricultural landscape has become more homogenous and a result, many species associated with traditional farmland or other semi-natural open habitats have declined. To be able to improve biodiversity conservation we need to be able to track components of biodiversity and understand how they respond to environmental changes. Biodiversity indicators can be very helpful in tracking such changes. However, species categorized as an indicator species for a certain habitat, might not exclusively occur in that habitat. In an intensely used landscape, with low amounts of natural and semi-natural habitats, some species may turn to use anthropogenic habitats such as forest clear-cuts. While these habitats might not categorize as grassland or farmland in our eyes, in some cases they seem to provide similar resources to farmland and grassland species. In this thesis, we compared multi-species indicators of farmland, grassland and forest butterflies and birds (Paper I) and found that indicators based on different taxa may send different signals even though they are based on the same habitat. Additionally, national trends might mask regional variation in trends. The literature review (Paper II) showed that farmland and grassland birds and butterflies do indeed occur on clear-cuts but the exact conditions that they need are often unclear. We then further explored the occurrence patterns of birds and butterflies in forest-clear cuts (Paper III and IV). We found that bird communities on clear-cuts changes with clear-cut age, size, vegetation height, the proportion of farmland in the near surroundings, and region. 10 out of 15 farmland bird indicator species occur on clear-cuts. They responded differently to environmental variables suggesting some might use clear-cuts as primary habitat in some regions and some might use clear-cuts more as complementary habitat while still depending on farmland in the surroundings. Clear-cuts are, however, not suitable for all farmland birds, most likely for reasons related to nesting sites, food, and predation risk.Butterfly communities on clear-cuts differ between the two surveyed counties as well as with clear-cut age and the proportion of open habitat and broadleaf forest in the surrounding landscape. Of the 20 farmland and grassland butterfly indicator species, 17 were observed on clear-cuts. While birds mostly responded to open habitat within a 200 m buffer of the clear-cuts, the butterflies more strongly responded to the larger scale 5 km landscape variables. Farmland bird abundance was often positively affected by clear-cut size while farmland and grassland butterflies, in the clear-cut centroids, were negatively affected by clear-cut size. This effect on butterflies was not seen in the edge of the clear-cuts, and this might indicate that butterflies either have a preference for the edges of the clear-cuts or use these lines in the landscape for orientation.While further studies are needed to expand our knowledge on how species, not least the currently declining grassland and farmland species, use these habitats to form more detailed management advice, the results in this thesis emphasize the importance of a landscape scale approach to conservation of both birds and butterflies. Forest clear-cuts could contribute to a green infrastructure for farmland and grassland birds and butterflies, however, the negative effect of forest clear-cuts on forest biodiversity as well as the climate needs to be taken into account when making conservation decisions