Book excerpt: Although biologists have directed much attention to estimating the extent and causes of species losses, the consequences for ecosystem functioning have been little studied. This book examines the impact of biodiversity on ecosystem processes in tropical forests - one of the most species-rich and at the same time most endangered ecosystems on earth. It covers the relationships between biodiversity and primary production, secondary production, biogeochemical cycles, soil processes, plant life forms, responses to disturbance, and resistance to invasion. The analyses focus on the key ecological interfaces where the loss of keystone species is most likely to influence the rate and stability of ecosystem processes.