Bumble bees collected in a large-scale field experiment in power line clearings, southeast Norway

Anthropogenic landscape elements, such as power line clearings, can be managed to provide important habitats for wild bees. However, the effects of habitat improvement schemes in power line clearings on components of diversity are poorly studied. We conducted a large‐scale experiment to test the effects of different management practices on bumblebees in power line clearings. Bumblebees were sampled using flight-interception traps at 19 sites during a large-scale field experiment within the main power-line grid in Southeast Norway. The 19 sites were located between latitudes 59.33°–61.12°N and longitudes 08.95°–11.36°E (WGS84) at 48–536 masl. The sites were mainly located in forested areas, consisting of the main tree species, Norway spruce (Picea abies (L.) H.Karst.), Scots pine (Pinus sylvestris L.) and birch (Betula spp.). Each site had been subjected to the same management regime with cutting of all woody vegetation every 5-10 years, without chemicals used, and had a stretch of at least 200 meters with substantial regrowth of trees before experiments were performed. The bee specimens were collected below power-lines in three 30 m x 60 m plots [corridor width], at least 20 m apart, where the vegetation was either; (1) cut: woody vegetation was cut and left to decay in the plot, (2) cut-remove: woody vegetation was cut and removed, (3) Vegetation was uncut. Within each treatment plot, three flight-interception traps (window traps) were set out immediately after snowmelt in 2013, 2014 and 2015. The flight interception traps consisted of two transparent Plexiglas screens (370 mm × 210 mm) that formed a cross, with a funnel and collecting bottle attached to it. The collecting bottle was filled with a 50:50 mixture of green propylene glycol and water, in addition to a drop of detergent. Every month we collected the bottles and immediately replaced them with new ones. The traps were emptied 4-5 times throughout the entire flowering season, from snowmelt in May to the end of the foraging activity‐season in September. This procedure ensured a continuous, standardized sampling among all sites. All bees were sorted and identified to species by Mari Steinert, Helene Totland Müller and Markus A.K. Sydenham. The cuckoo bumblebees and some specimens of each species are pinned. All of the material is stored at the Norwegian university of Lifesciences (NMBU).