Effects of vegetation clearing and dead wood on beetles in power line clearings southeast Norway

Linear habitats, such as power-line clearings, have been thought to affect biodiversity negatively. However, during the last decade several studies have highlighted the potential value of power-line clearings as habitats for a number of taxonomic groups, like bees and butterflies. The vegetation below power-lines is continuously reset to earlier successional stages, which provides suitable habitats for several native plant species, which hosts diverse assemblages of pollinating insects. In addition, the dead wood and biomass from the vegetation clearing, together with tree falls along the clearing edges may be important habitats for xylophagous beetles. With proper management, power-line clearings could be important for conservation of species associated with open-canopy habitats and dead wood.

We conducted a large-scale field experiment, with 19 sites haphazardly distributed within the main power line grid in southeast Norway. All sites were placed below power lines in a boreal forest system consisting of varying proportions of the main tree species: Norway spruce Picea abies, Scots pine Pinus sylvestris and birch Betula spp. Sites were located between latitudes 59.33°–61.12°N and longitudes 08.95°–11.36°E at 48–536 m a.s.l., varying in width and age. 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. At each site, we established three plots of approx. 30 x 60 m, at least 20 m apart. During late autumn 2012 (16 sites) and early spring 2013 (3 sites), treatments were randomly allocated to each of the plots within a site: 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 a 10m × 10m plot in the centre of each treatment, we measured amount and type of dead wood (volume, species, diameter, degree of decay). In each experimental treatment, we also deployed insect traps (three flight intersection for trapping insects from spring to early autumn), and measured microclimatic conditions (light, temperature, precipitation) and various habitat attributes (tree layer characteristics, canopy density). Field data collections on vascular plants, insects, dead wood, habitat characteristics and microclimatic conditions have been collected over a three-year period (2013-2015). All insect specimen have been sorted into orders and all the beetles have been identified to species by Sindre Ligaard (Beetles: approx 48 000 specimen).