Present situations of forest damage in the United States and in Europe were outlined. From the data it was indicated that foliar injury or inhibition of growth of plants were detected by the exposure to acid rain below pH 3.0. Effects of acid rain on forest ecosystems were summarized as follows: (1) Depositions of air pollutants on forest floors were much larger in coniferous forests than in broadleaved forests, (2) Base cation leaching from leaf surface and soil layers were increased by acid rain below pH 4.(3) Extractions of exchangeable Al from soil were increased below 5 in soil pH in acidic brown forest soil, where the deposition of SO4-S of 100gS/m2 land area will decrease to 5 in soil pH. It was estimated that the mentioned amount of SO4-S deposition will attain in 30 years in cryptomeria forests and in 40 years in Quercus forests in Tokyo. However, several possibilities to induce forest decline have been proposed by resent works in U. S. and in Europe, where principal pathways to cause forest decline are still unclarified. Perspectives of future needs of countermeasures in our country were also discussed.
