Acidic deposition and its effects on the forests of Nordic Europe

Air pollution effects on the forest of Nordic Europe are analyzed with respect to the situation before and after 1980. No adverse effects were reported up to 1980. Inventories of forest vitality in terms of needle loss or crown density as well as tree growth have been made in parts of Norway and the whole of Sweden. For Norway spruce, needle loss was found to increase with tree age and climatic stress with increasing latitude and altitude. However, decreased crown density was also reported for SW Sweden. Needle loss is a non-specific signal not reacting to air pollution alone. Direct effects of gases such as SO₂ are not likely to occur, but high episodic levels of O₃ have been measured at a level possibly leading to chronic injuries. Increasing soil acidity is reported from forests in SW Sweden and also from an alpine locality in southern Norway. A differentiation of biological and deposition-dependent acidification has been attempted. A soil acidification of up to 1 pH unit has occurred in both humus and mineral soil layers. An increased release of A1 and heavy metals combined with an increased loss of basic cations is now occurring. Soil acidification probably also results in less available amounts of phosphorus and is suggested to interact with N as limiting forest growth.