This paper summarizes the results from current studies in Norway. One main approach is the application of artificial acid 'rain' and of lime to field plots and lysimeters.
Application during two growth seasons of 50 mm mo -~ of 'rain water' of pH 3 to a podzol soil increased the acidity of the humus and decreased the base saturation. The reduction in base saturation was mainly due to leaching of Ca and Mg.
Laboratory experiments revealed that decomposition of pine needles was not affected by any acid 'rain' treatment of the field plots. Liming slightly retarded the decomposition.
No nitrification occurred in unlimed soils (pH 4.4-4.1). Liming increased nitrification.
The soil enchytraeid (Ofigochaeta) fauna was not much affected by the acidification. Germination of spruce seeds in acidified mineral soil was negatively affected when soil pH was 4.0 or lower. Seedling establishment was even more sensitive to increasing soil acidity.
Analysis of throughfall and stemflow water in southernmost Norway reveals that the total deposition of H2SO 4 beneath spruce and pine is approximately two times the deposition in open terrain. A large part of this increase is probably due to dry deposition. Increased acidity of the rain seems to increase the leaching of cations from the tree crowns.
Tree-ring analysis of spruce (Picea abies (L.) Karst.) and pine (Pinus sylvestris L.) has been based on comparisons between regions differently stressed by acid precipitation and also between sites presumed to differ in sensitivity to acidification. No effect that can be related to acid precipitation has yet been detected on diameter growth.