Depending on their concentrations, air pollutants are dangerous to forests. With the exception of some industrial areas in the east, concentrations of air pollutants in Central Europe are below the damaging threshold as shown by the records of the monitoring stations.

Atmospheric pollutant can cause direct effects mediated by foliage and indirect effects mediated through soil. Biotic and abiotic factors can confound relationships among nutrient cycling, growth loss and mortality and air pollution. Changes in the soils could result from acidic deposition. Changes could include increased fertility as a result of sulphur and nitrogen input to soils that are deficient in these elements or decreased fertility through ion leaching or mobilization of toxic substances as aluminium.

The soil biota plays a critical part in the functioning of forest ecosystems. Acidification and heavy metals have the greatest direct effects on the soil biota. However pollutants can have indirect effects through their influence on tree root systems. Acidic deposition can decrease the incidence of mycorrhizal infection, but soil pH and concentration of nitrogen and certain forms of sulphur are also important.

Information on potential forestry losses seems to be crucial to government officials that they can properly assess the costs and benefits of limiting pollution and greenhouse gas emissions. However very few socio-economic assessments of potential losses have been completed.

Climate change will be the major impact on all forests, included increased risk of large-scale fires, enhanced susceptibility to insects and diseases. Direct effects of air pollution on vegetation include damage to protective surface structures, disturbance of photosynthesis.

Considerable uncertainty has surrounded the relationship between forest growth and forest declines in Europe. Although growth decreases have been recorded in several years, by the end of the 1980s, increment at many sites had reached a level higher than any previously recorded. Fertilization by carbon dioxide, favourable climatic conditions and better stand management may all have contributed.

Two main effects on ectomycorrhizae can be distinguished: direct effects due to a change in the soil chemistry and indirect effects due to a change of the carbohydrate supply from the host trees to the roots.

Wood will have a great importance as renewable raw material. Forest devastation endangers the world's future wood supply. We need a long-term strategy for forestry and forest products industries to protect complete ecological life cycle.

The report summarizes scientific information about forest ecosystems and their relationship to climate change and air pollution, with special emphasis on forests in Europe, North America and China. The contributions reflect the current state of science, but also uncertainties and gaps in scientific knowledge.

Monitoring of forest health represents an important part of programmes assessing the actual and potential impact of air pollution and climate change on forests. The available information indicates that variation between years is high, indicating that long term time series will be required to identify trends in forest condition.