A. Shevtsova et S. Neuvonen, RESPONSES OF GROUND VEGETATION TO PROLONGED SIMULATED ACID-RAIN IN SUB-ARCTIC PINE-BIRCH FOREST, New phytologist, 136(4), 1997, pp. 613-625
The effects of prolonged simulated acid rain on percentage cover of gr
ound vegetation, and on growth and reproduction of two dominating dwar
f shrubs (Empetrum nigrum and Vaccinium vitis-idaea) were examined in
a field experiment in the Finnish Subarctic, in an area with low ambie
nt levels of sulphur and nitrogen deposition. Acid rain treatments inc
luded moderate (pH 3.8) and high (pH 2.9) concentrations of either H2S
O4, or HNO3, or a mixture of them, and were compared with irrigated (p
H 6) and dry control plots. Long-term application of acid rain caused
significant alteration in the cover and composition of ground vegetati
on. Effects of acid rain depended on the accompanying anion and on pH.
Sub-plots under different canopy tree species differed in responses i
ndicating that spatial heterogeneity is important in predicting the ef
fect of acidifying pollution on this plant community. In the bottom la
yer, acid rain caused significant reduction in cover of the cyanobacte
rial lichens Nephroma arcticum and Peltigera spp. Decrease in cover of
fruticose lichens, mainly composed of Cladina spp., more likely resul
ted from additional watering. In the field layer, acid rain containing
moderate concentrations of NO3- caused an increase in cover of gramin
oid species. There were only slight alterations in growth and cover of
the two 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, dep
ending 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 th
e nitric acid only was applied, a short-term increase in the number of
new shoots of E. nigrum. In contrast to vegetative growth, reproducti
on of the dwarf shrubs was more strongly affected by acid rain, but th
is also depended on local conditions and anion composition of acid rai
n. On 'pine' plots, rain of pH 3 reduced the number of berries and flo
wer buds on terminal current shoot of E. nigrum, however, this was par
tially compensated by an increase in berry production at the ramet lev
el. Simulated acid rain had mainly negative effects on berry productio
n by V. vitis-idaea.