the future. Quantifying and predicting the effects of these changes on ecosys­ tem functioning are achallenge to ecosystem research and also a requirement to establish sustainable use of forest ecosystems in the future. This book summarizes results of long-term, interdisciplinary ecosystem research conducted in two forested catchments and coordinated at the Bayreuth Institute of Terrestrial Ecosystem Research (BITÖK), University of Bayreuth, Germany. It does not aim to summarize all the research of BITÖ K in the past decade, which would go far beyond the studies in these two catch­ ments. Instead, we concentrate here on the long-term developments in the biogeochemistry of carbon and mineral elements and on the water cyde, at both the plot and the catchment scale.