Effects of global change on a sub-Arctic heath: effects of enhanced UV-B radiation and increased summer precipitation

1 The responses of sub-Arctic heathland vegetation to enhanced UV-B radiati on and increased summer precipitation over 7 years were investigated in a f ield experiment in northern Sweden. 2 Growth, phenology and reproduction of the dominant dwarf shrubs Vaccinium myrtillus, V. uliginosum, V. vitis-idaea and Empetrum hermaphroditum were studied after 5-7 years of manipulation and retrospective analyses were use d to assess growth responses in earlier years. Leaf tissue N and P and C-13 natural abundances were determined for V. myrtillus and E. hermaphroditum. Growth responses were also assessed for the moss Hylocomium splendens. 3 The deciduous V. myrtillus showed reduced growth, increased leaf thicknes s and increased flowering and berry production under enhanced UV-B in some years. V. uliginosum, V. vitis-idaea, E. hermaphroditum and H. splendens we re, in general, tolerant of UV-B. 4 Increased precipitation affected growth only in the evergreen species: st em length and branching were sometimes stimulated in E. hermaphroditum, whe reas V. vitis-idaea showed reduced branching. 5 Precipitation also increased leaf thickness in V. uliginosum and reduced flowering and berry production in V. myrtillus. 6 In the interactions that occurred between enhanced UV-B radiation and inc reased summer precipitation, combining the two treatments often negated any effect that either may have had separately. The effect of concurrent incre ases on this ecosystem is therefore likely to be much less than if either o ccurred singly. 7 Enhanced UV-B and increased summer precipitation appeared not to effect d warf shrub abundances during the first 5 years of the experiment, suggestin g that overall this heath may be more tolerant of these environmental chang es than previously thought.