Air pollution has been recognized as a potential problem for forests for nearly 150 years. Today, sulphur dioxide, fluorides, heavy metals and ozone are a significant problem, usually from large scale sources in industrial and urban areas. Problems are exacerbated in those regions where there is a poor understanding of the factors involved in forest decline and destruction and no rigorous control over it has been established. This book is a report from the International Union of Forest Research Organization’s (IUFRO) Task Force on Environmental Change and provides an assessment of the extent of air pollution impacts on forests in heavily polluted regions. It includes case studies from Russia, Ontario (Canada), California and the Mediterranean region.