The effects of prolonged simulated acid rain on percentage cover
ground vegetation, and on growth and
reproduction of two dominating dwarf shrubs (Empetrum nigrum and
Vaccinium vitis-idaea) were examined in a
field experiment in the Finnish Subarctic, in an area with low ambient
sulphur and nitrogen deposition.
Acid rain treatments included moderate (pH 3·8) and high (pH 2·9)
concentrations of either H2SO4, or HNO3,
a mixture of them, and were compared with irrigated (pH 6) and dry control
Long-term application of acid rain caused significant alteration in
the cover and composition of ground
vegetation. Effects of acid rain depended on the accompanying anion and
Sub-plots under different canopy
tree species differed in responses indicating that spatial heterogeneity
important in predicting the effect of
acidifying pollution on this plant community.
In the bottom layer, acid rain caused significant reduction in cover
cyanobacterial lichens Nephroma
arcticum and Peltigera spp. Decrease in cover of fruticose
lichens, mainly composed of Cladina spp., more likely
resulted from additional watering.
In the field layer, acid rain containing moderate concentrations of
NO3− caused an increase in cover of graminoid
species. There were only slight alterations in growth and cover of the
dominant evergreen dwarf shrubs, E.
nigrum and V. vitis-idaea, indicating that these species
are tolerant to acid rain of as low as pH 3. Even some
positive responses of dwarf shrubs were observed, depending on canopy tree.
Application of acid rain of pH 3 to
plots under pine trees caused an increase in cover of V. vitis-idaea
and, when the nitric acid only was applied, a
short-term increase in the number of new shoots of E. nigrum.
In contrast to vegetative growth, reproduction of the dwarf shrubs
was more strongly affected by acid rain, but
this also depended on local conditions and anion composition of acid rain.
On ‘pine’ plots, rain of pH 3 reduced
the number of berries and flower buds on terminal current shoot of
E. nigrum, however, this was partially
compensated by an increase in berry production at the ramet level.
Simulated acid rain had mainly negative effects
on berry production by V. vitis-idaea.