Preface.- A concept of forest ecosystem stability and of acid deposition as driving force for destabilization.- Topic 1: Processes and Rates of Deposition, Storage Places of Deposited Air Pollutants.- Interaction of forest canopies with atmospheric constituents: SO2, alkali and earth alkali cations and chloride.- Interaction of forest canopies with atmospheric constituents: Aluminum and heavy metals.- Input of acidifiers and heavy metals to a German forest area due to dry and wet deposition.- Processes and rates of deposition of air pollutants in different ecosystems.- Measurements of surface resistance during dry deposition of SO2 to wet and dry coniferous forest.- Topic 2: Processes and Rates of Proton Production by Discoupling of the Ion Cycle, and of Proton Consumption by Silicate Weathering.- The turnover of protons by mineralization and ion uptake in a beech (Fagus Silvatica) and a Norway spruce ecosystem.- Effects on soil chemistry as a consequence of proton input.- Holocene versus accelerated actual proton consumption in German forest soils.- Topic 3: Effects on Chemical Soil State.- Soil acidity and its relations to acid deposition.- Balances of element fluxes within different ecosystems impacted by acid rain.- A mechanism for storage and retrieval of acid in acid soils.- Effects of atmospheric ammonium sulfate on calcareous and non-calcareous soils of woodlands in the Netherlands.- Studies of proton flux in forests and heaths in Scotland.- Composition of percolate from reconstructed profiles of two Jack Pine Forest soils as influenced by acid input.- Sulphur pollution: Ca, Mg and Al in soil and soil water and possible effects on forest trees.- Soil properties under three species of tree in southern England in relation to acid deposition in throughfall.- Influence of soil reaction and organic matter on the solubility of heavy metals in soils.- Topic 4: Effects on Biological Soil State and on Animals.- Micro-morphological characteristics of humus forms as indicators of increased environmental stress in Hamburg’s forests.- Biochemical reactivity in forest soils as indicators for environmental pollution.- Mercury - Accumulation in game.- Topic 5: Effects of Soil Acidification and Accumulation of Air Pollutants on Plants.- Air pollutant deposition and effects on plants.- IUFRO-Studies on maximal SO2 emissions standards to protect forests.- Longtermed fluoride pollution of a forest ecosystem: Time, the dimension of pitfalls and limitations.- The problem of determining growth losses in Norway Spruce stands caused by environmental factors.- First information about inventory of emission depending damages on Norway Spruce in Lower Saxony/Fed. Rep. Germany.- Die-back of Red Spruce, acid deposition, and changes in soil nutrient status - a review.- Scots Pine-dying within the neighbourhood of an industrial area.- Growth patterns, phloem nutrient contents and root characteristics of beech (Fagus sylv.L.) on soils of different reaction.- Biological alterations in the stem and root of fir and spruce due to pollution influence.