INTERRELATIONSHIPS BETWEEN TREELINE POSITION, SPECIES-DIVERSITY, LAND-USE AND CLIMATE-CHANGE IN THE CENTRAL SCANDES-MOUNTAINS OF NORWAY

Vegetation samples collected along altitudinal transects through the t reeline ecotone in the central Scandes Mountains, Norway, were used to analyse the relationships between species diversity, species turnover and the performance of the tree layer. The study area has a long hist ory of extensive grazing by domestic animals. The floristic compositio n showed a continuous change along the boreal-alpine gradient. The num ber of species was more or less constant throughout 600 altitudinal m centred around the treeline, and the Aoristic similarity between neigh bouring altitudes did not show any abrupt changes at any particular al titude. The treeline position (Betula pubescens Ehrh.) spanned 190 alt itudinal m (range 980-1170 m a.s.l.). The number of trees and the basa l area each decreased continuously with increasing altitude from 300 a ltitudinal m below the treeline. The number of birch saplings also dec reased from c. 150 m below the treeline towards higher altitudes. Viab le, but browsed populations of birch were present along the whole leng th of all transects, irrespective of aspect and geological substrate, with saplings present up to summit positions at 420 altitudinal m abov e the treeline. Due to browsing by sheep, mean sapling height at all a ltitudes above the treeline was 0.2 m. The results are discussed in te rms of land use and climate change. It is concluded that future vegeta tion responses to diminished grazing pressure are likely to override r esponses forced by changing climate. Such responses could easily be mi sinterpreted as being governed by climate change, rather than by chang es in land use.