Effects of vegetation clearing on vascular plants 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 species. With proper management, power-line clearings could be important for conservation of species associated with open-canopy habitats. 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. We placed a systematic grid with nine plant-plots of 1m2 within each treatment plot, and visually quantified % abundance of all vascular plants the following seasons. The plant-plots were regularly spaced within a 10m × 10m subplot located in the centre of each treatment plot. Registrations were carried out in late June/early July in 2013, 2014 and 2015. If a species was present in a subplot, but had < 1% cover, it was recorded as 0.001%. The field data collections are funded by Statnett, and designed to study effects of vegetation clearing on biodiversity (i.e. vascular plants and insects) under power line clearings.