When Springer-Verlag undertook publication of this volume, two opportunities arose. The first was to bring together the significant findings ofthe interacting parts of a large field experiment on a whole ecosystem. Scientific specialists and the public are rightly concerned with large-scale impacts of human activity on landscapes and with the challenge of predicting subtle, long-range repercussions of air pollution. A fundamental issue is whether ecological systems like grasslands, which have evolved for several million years under stressful conditions such as variable climate and...