This volume presents results from an integrated research programme "Effects of Air Pollutants and Acidification" funded by the Swedish Environmental Protection Agency (SNV) between 1988/89 and 1992/93. The programme has focussed on the fluxes and environmental effects of acidifying substances and tropospheric ozone in terrestrial, natural ecosystems. During the programme period, 71,5 million SEK were allocated to about 60 projects at different Swedish universities and research institutes. Most of the contributions in this book are original articles based on results from some of these projects. In addition, there are some papers reviewing earlier and recent research. When considered as a whole, the published papers represent all major areas of research addressed within the programme. A publication list from the programme is given at the end of the volume. Comprehensive research on the ecological effects of acidifying substances has been carried out in many countries in Europe and North America since the 1970s. In Sweden, the SNV initiated such research a few years after Svante Oden presented his "discovery" of the Acid Rain problem. Since 1977, Swedish acidification research has been organized as integrated programmes, initially concentrated on water and soil acidification but gradually including projects on forest damage. From 1988/89 and onwards the research has been divided into different programmes with participation from several funding agencies. In 1988, the Swedish Environmental Protection Agency started two programmes for studying teh effects of acidification and other air pollution problems in natural ecosystems; one on surface waters and one dealing with the terrestrial environment. Later, a third programme dealing with effects on human health was initiated. Other agencies have administered research on the impact of air pollution on crops, technical materials, historical buildings and monuments, below-ground constructions, and archaeological sites. Much of the research concerning the terrestrial environment has been performed in forest ecosystems, the reason being that almost 60% fo Sweden is covered by forests, and that forests play a very important role in Sweden's economy and as a source of recreation. Furthermore, studies of soils and how they react to acid deposition has been a major research theme. Today, most scientists consider soil changes as the major pollutionmediated threat to forest organisms in southern Sweden, while tropospheric sozone is considered to be the most important gaseous pollutant.
