Trends in sulphate deposition on the forests and forest floor and defoliation degree in 16 intensively studied forest stands in Finland during 1996–2003

Deposition samples (bulk deposition, stand throughfall) were collected in 8 Norway spruce and 8 Scots pine stands throughout the year in Finland during the period 1996–2003. Defoliation was also estimated annually in the same stands. Sulphate deposition in Finland during the period 1996–2003 decreased, the decrease being most evident at the beginning of the period. Sulphate deposition in the northern part of the country has been considerably lower than that in the southern part of the country, and therefore the decrease during the period 1996–2003 in the northern part of the country has been relatively insignificant. In the eastern part of Finland, which receives a considerable proportion of the sulphate deposition from the St. Petersburg area and the shale-oil power stations in NE Estonia, there were no clear decreasing trends in sulphate deposition. The decrease in sulphate deposition elsewhere in the country was mainly due to the decrease in the sulphate concentrations since the amount of precipitation did not decrease during the monitoring period.There was a clear decreasing gradient running from southern to northern Finland in the net-throughfall of sulphate from the tree canopies in both the spruce and pine stands. No clear decrease was observed in defoliation on any of the plots during the study period, although sulphate deposition decreased significantly during 1996–2003. Sulphate deposition alone is not, at current levels in Finland, likely to cause changes in forest health in terms of defoliation in the short term at least.