The biggest problem facing the forest of Latin America is deforestation. Air pollution also constitutes a threat to some forests, and pollution level will increase in the future. Major problem associated with photochemical smogs have been documented in the mountains around Mexico City and Santiago in Chile. Acidic deposition has been identified in some areas and is known to be affecting forest reserves in rural situations.

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.

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.