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.

Air pollutants such as ozone may affect tree host-pathogen interactions by altering plant tissue susceptibility, plant resistance, pathogen virulence and inoculum density. Ozone has been shown to weaken trees in natural stands and increase their susceptibility to invasion by plant pathogens, such as Heterobasidion annosum. Ozone has also been shown to enhance disease development by fungi that are normally saprophytic in nature.

The potential effects of long-term exposures to widespread low but raised concentrations above natural levels in Central Europe are still being discussed. This uncertainty results from an inadequate mechanistic understanding of the influence of air pollutants and other environmental factors of trees.

The ranges of the ecosystems move when the climatic pattern changes. Simulations have shown that a global warming would cause important changes of the species composition in subalpine forests. Deciduous trees would invade today's subalpine belt. Various conifers would be displaced and migrate into alpine zone. The model simulations are based on the IPCC climate scenarios.

Long-term changes in forest soils are characterised by decreases in soil pH, exchangeable base cations, percent base saturation and accumulation of heavy metals. Acidic deposition effects on forest soils can be demonstrated experientially either in the laboratory or in the field by stimulated acid treatments.

There is a strong evidence to indicate that sulphates and nitrogen oxides cause increased leaching of base cations, principally calcium and magnesium from soils supporting old-growth sugar maple forest in central Canada. Sugar maple trees sequester Ca, especially in bark. A site low in exchangeable bases might become less productive, if subjected to prolonged high rates of leaching and full tree harvesting.

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.

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.