Power line clearings : suitable habitat for semi-natural grassland species?
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- Master's theses (INA) 
Owing to land-use changes, abandoning and intensification of agriculture, semi-natural grasslands are becoming increasingly scarce all over Europe. As a consequence many of the species associated with these habitats have become rare or threatened. Power line clearings are in general viewed as a negative disturbance in forest landscapes. On the other hand, it has been suggested that power line clearings, road verges, and similar human-made landscape elements can act as replacement habitat for semi-natural grassland species. We carried out a large-scale field experiment in power line clearings intersecting boreal forests. All the clearings had a history of management where all woody vegetation was cut every 5-10 years and all biomass was left to decay on site. We selected 19 sites in the main power line grid in southeast Norway. Three different treatments were applied on each site: 1) Cut: All woody vegetation was cut and the cut biomass removed 2) Cut + Remove: all woody vegetation was cut and left to decay on site 3) Uncut: uncut control. We investigated the total species richness of vascular plants in the field layer and richness of semi-natural grassland species (this group also contains species from open forest) in the different treatments. We also investigated which factors affected total species richness and richness of semi-natural grasslands species in the power line clearings. Treatments Cut and Cut + Remove had significantly higher species richness than Uncut. Increasing landscape fragmentation within a 1 km radius from the treatment plots had a significant positive effect on both total species richness and richness of semi-natural grassland species. There was no difference among treatments the first year after the vegetation was cut for either total species richness, or richness of semi-natural grassland species. In the second and third year after cutting, however there was a significantly higher species richness in 4 the treatments Cut and Cut + Remove when compared to treatment Uncut for both total species richness and semi-natural grassland species. We could not conclude that power line clearings can be a replacement habitat for semi- natural grassland species based on the species found in the clearings. However power line clearings can possibly act as a supplementary habitat and thereby mitigate loss of semi-natural grassland species. In cases where the power line clearings intersect species poor, dense forest managed for timber production they will probably contribute to increased species richness on a local scale and possibly mimic open forest.