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
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.