THE EFFECTS OF ENHANCED UV-B RADIATION ON A SUB-ARCTIC HEATH ECOSYSTEM

To investigate the effects of increased UV-B radiation on a natural su barctic ecosystem a field irradiation experiment was established at Ab isko, northern Sweden. The vegetation in the plots consists of a dwarf shrub layer with mosses and lichens beneath. Many response variables of the vegetation and soil are measured in these plots, e.g. photosynt hesis, growth, phenology, changes in species composition and decomposi tion. This paper describes the methods used and some initial results. Decomposition was imparied by enhanced UV-B radiation. UV-B directly a ffected decomposition processes and also affected them indirectly by a ltering the tissue chemistry of leaves. The annual growth of the dwarf shrubs was lower under enhanced UV-B. This was more pronounced in eve rgreen than in deciduous species. Leaf thickness of the dwarf shrubs w as changed by UV-B. The leaves of the evergreen Vaccinium vitis-idaea grew thicker, while those of the two deciduous species V. myrtillus an d V. uliginosum grew thinner. In the moss Hylocomium splendens, the ph enological development was accelerated under enhanced UV-B radiation. Its growth (number of primary branches, length and dry weight) also in creased.