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 si mulate 15% ozone depletion under clear sky conditions in northern Swed en. This was accomplished by using UV-B fluorescent lamps mounted on m etal frames raised over a naturally growing plant community. 2. The st udy area consisted of a dwarf shrub heath mainly composed of the four species Vaccinium vitis-idaea, V. myrtillus, V. uliginosum and Empetru m hermaphroditum. The absolute annual stem growth, relative stem growt h and absolute leaf growth were recorded for different years. 3, The r elative growth was significantly reduced by UV-B enhancement in the tw o 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 gr owth under enhanced UV-B, but this effect was not statistically signif icant. 4. The leaf thickness of V. vitis-idaea increased both during 1 992 (9%) and 1993 (4%). In contrast, the two deciduous species V. myrt illus and V. uliginosum developed thinner leaves under enhanced UV-B b oth during 1992 (4% for V. myrtillus, 6% for V. uliginosum) and 1993 ( 9% for V. myrtillus, 10% for V. uliginosum).