THE EFFECTS OF ENHANCED UV-B RADIATION ON THE GROWTH OF DWARF SHRUBS IN A SUB-ARCTIC HEATHLAND

1. In a field irradiation experiment UV-B radiation was enhanced to simulate 15% ozone depletion under clear sky conditions in northern Sweden. This was accomplished by using UV-B fluorescent lamps mounted on metal frames raised over a naturally growing plant community. 2. The study area consisted of a dwarf shrub heath mainly composed of the four species Vaccinium vitis-idaea, V. myrtillus, V. uliginosum and Empetrum hermaphroditum. The absolute annual stem growth, relative stem growth and absolute leaf growth were recorded for different years. 3, The relative growth was significantly reduced by UV-B enhancement in the two evergreen species V. vitis-idaea (27% after 2 years of enhanced UV-B) and E. hermaphroditum (14% after 1 year and 33% after 2 years). The two deciduous species also showed a tendency for decreased relative growth under enhanced UV-B, but this effect was not statistically significant. 4. The leaf thickness of V. vitis-idaea increased both during 1992 (9%) and 1993 (4%). In contrast, the two deciduous species V. myrtillus and V. uliginosum developed thinner leaves under enhanced UV-B both during 1992 (4% for V. myrtillus, 6% for V. uliginosum) and 1993 (9% for V. myrtillus, 10% for V. uliginosum).