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%. We were unable to identify all plants to species, due to registrations being early in the season, and as some taxa are difficult to distinguish (e.g. Taraxacum sp., Hieracium sp.). 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.