Forest decline: A problem for Europe and North America

Forest decline was one of the most debated environmental issues throughout the 1980s: the action exerted by air pollution on forests was seen as a threat that would eventually lead to the collapse of these ecosystems. Several research and monitoring projects were thus set up both in Europe and in North America in order to investigate and control the phenomenon. A review of the results achieved over the past 15-20 years has enabled the rapporteurs to reduce the scale of this alarm: forests no longer appear to be on the verge of extinction as a result of trans-boundary pollution, although a great many problems still persist. At a local scale, air pollutants can cause severe damage (the "black triangle" in Central-Eastern Europe; acidification of lakes and soil in Central Northern Europe; surfactant damage along the coastal areas of the Mediterranean), whereas we still know very little about the long-term effects of ozone. This substance, which is found at levels suspected to be toxic both in densely populated and in remote areas, is today a real global stress factor for forests. The symposium also discussed issues related to long-term monitoring of forest ecosystems and addressed the fact that the indices used to date are not suitable for an in-depth study of the action exerted by air pollution. The conclusions highlight the problems that must be addressed in order to improve our information potential in forest decline surveys.