To investigate the effects of increased UV-B radiation on a natural subarctic ecosystem a field irradiation experiment was established at Abisko, 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. photosynthesis, growth, phenology, changes in species composition and decomposition. This paper describes the methods used and some initial results. Decomposition was imparied by enhanced UV-B radiation. UV-B directly affected decomposition processes and also affected them indirectly by altering the tissue chemistry of leaves. The annual growth of the dwarf shrubs was lower under enhanced UV-B. This was more pronounced in evergreen than in deciduous species. Leaf thickness of the dwarf shrubs was changed by UV-B. The leaves of the evergreen Vaccinium vitis-idaea grew thicker, while those of the two deciduous species V. myrtillus and V. uliginosum grew thinner. In the moss Hylocomium splendens, the phenological development was accelerated under enhanced UV-B radiation. Its growth (number of primary branches, length and dry weight) also increased.