This volume contains papers presented at a NATO Advanced Research Institute, sponsored by their Eco-Sciences Panel, on "The effects of acid precipitation on vegetation and soils," held at Toronto, Canada from May 22-26, 1978. The organizing expenses and greater part of the expenses of the speakers and chair~en were provided by N.A.T.O. The scientific programme was planned by T. C. Hutchinson together with an international planning committee of G. Abrahamsen (Norway), G. Likens (U.S.A.), F.E. Last (U.K.), C.O. Tamm (Sweden) and B. Ulrich (W. Germany). Many of the dimensions of the 'acid rain' problem are common to countries of northern Europe and North America. The developing awareness over the past ten years of the international nature of the acid rain phenomenon has lead to studies documenting damaging effects on susceptible freshwater bodies. Large areas of the Canadian Pre-Cambrian Shield, with its extension into the United States, and the granitic areas of southern Norwayand Sweden contain lakes which are in the process of acidification. The biological resources of these affected areas are of considerable national concern. However, while clearly damaging effects of acidification on freshwater systems have been well documented, the impact of acid precipitation on terrestrial systems has not been so well understood.

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Conference Address.- I. The Nature of Precipitation Reaching the Forest Canopy and the Ground.- 1. Wet and Dry Deposition of Sulfur and Nitrogen Compounds from the Atmosphere.- 2. An Estimation of the Atmospheric Input of Acidifying Substances to a Forest Ecosystem.- 3. Sulfur Dioxide Absorbed in Rain Water.- 4. Difficulties in Measuring Wet and Dry Deposition on Forest Canopies and Soil Surfaces.- 5. Wet and Dry Deposition of Sulfur at Hubbard Brook.- 6. Acid Snow - Snowpack Chemistry and Snowmelt.- 7. Ion Relationship in Acid Precipitation and Stream Chemistry.- 8. The Sulfur Budget of Sweden.- II: The Effect of Acidic Atmospheric Inputs on Vegetation.- A: Direct Effects.- 9. Some Special Features of the Ecophysiological Effects of Air Pollution on Coniferous Forests During the Winter.- 10. Regional and Local Effects of Air Pollution, Mainly Sulfur Dioxide, on Lichens and Bryophytes in Denmark.- 11. Some Effects of Rain and Mist on Plants, with Implications for Acid Precipitation.- 12. Experimental Studies on the Phytotoxicity of Acidic Precipitation: The United States Experience.- B. The Influence of Vegetation in Modifying Atmospheric Inputs to the Soil.- 13. Assessing the Contribution of Crown Leaching to the Element Content of Rainwater Beneath Trees.- 14. Input to Soil, Especially the Influence of Vegetation in Intercepting and Modifying Inputs - A Review.- III: Effect of Acid Precipitation on Soils.- 15. The Acidification of Soils.- 16. Effect of Low pH on the Chemical Structure and Reactions of Humic Substances.- 17. Podsolization: Mechanisms and Possible Effects of Acid Precipitation.- 18. Interaction Between Cations and Anions Influencing Adsorption and Leaching.- 19. Production and Consumption of Hydrogen Ions in the Ecosphere.- IV: Effect of Soil Acidity onPlant Nutrition, Mineral Cycling and Soil Microbial Activity.- 20. The Effects of Soil Acidity on Nutrient Availability and Plant Response.- 21. Effects of Artificial Acid Rain on the Growth and Nutrient Status of Trees.- 22. Forest Ecosystem Responses to Acid Deposition-Hydrogen Ion Budget and Nitrogen/Tree Growth Model Approaches.- 23. Predicting Potential Impacts of Acid Rain on Elemental Cycling in a Southern Appalachain Deciduous Forest at Coweeta.- 24. Effects of Artificial Acid Rain and Liming on Soil Organisms and the Decomposition of Organic Matter.- 25. Effects of Acidity on Microorganisms and Microbial Processes in Soil.- 26. Soil Organisms and Litter Decomposition in a Scots Pine Forest-Effects of Experimental Acidification.- 27. Effects of Sulphur Deposition on Litter Decomposition and Nutrient Leaching in Coniferous Forest Soils.- 28. Smelter Pollution near Sudbury, Ontario, Canada, and Effects on Forest Litter Decomposition.- 29. Effects of Rainfall Acidification on Plant Pathogens.- V. The Influence of Acid Precipitation on Soil Inputs to Water.- 30. Variations in Precipitation and Streamwater Chemistry at the Hubbard Brook Experimental Forest During 1964 to 1977.- 31. Effects of Acid Deposition Upon Outputs from Terrestrial to Aquatic Ecosystems.- 32. Effects of Acid Leaching on Cation Loss from Soils.- 33. Studies of Acid Rain on Soils and Catchments.- VI: Identification of Sensitive Sites and Soils.- 34. Site Susceptibility to Leaching by H2SO4 in Acid Rainfall.- 35. Ion Adsorption Isotherms in Predicting Leaching Losses from Soils due to Increased Inputs of Hydrogen Ions - A Case Study.- 36. The Sensitivity of Soils to Acid Precipitation.- 37. The Sensitivity of Soils to Acidification.- 38. Sensitivity of Different Soils to AcidPrecipitation.- VII: Meeting Summaries Rapporteurs Reports.- A. Wet and Dry Deposition Including Melting Phenomena and Snowpack Chemistry.- B. Direct Effect of Atmospheric Deposition on Plant Growth.- C. Inputs to Soil: The Influence of Vegetation.- D. Effects of Acid Precipitation on Soils.- E. Effects of Soil Acidity on Nutrient Availability and Plant Response.- F. Effects of Acidity on Nitrogen Cycling.- G. Effects of Acidification on Soil Microbes, Including Decomposition Processes.- H. Effects of Acid Precipitation on Plants and Plant Pathogens.- I. Effect of Acid Precipitation on Water Quality, and on Effects via Soil into Water Bodies.- J. Identification of Sensitive Sites and Soils.- VIII: Conclusions and Recommendations.- List of Participants.- Species Index.