The Ogawa Forest Reserve (OFR) is a species-rich, temperate, deciduous, old-growth forest in central Japan in which the ecology of the tree community has been intensively investigated since 1987. Detailed demographic data on the main tree species, covering the entire tree life cycle, were collected to elucidate the mechanisms by which community structure, organization, and species diversity are maintained. Included here is the work of more than 40 scientists in such diverse fields as botany, ecology, pedology, silviculture, mammal ecology, entomology, and ornithology, who have studied the same forest at the same time. This volume introduces the main areas of research under the OFR project and discusses the implications of the results on environmental issues. Integrated studies of this type are essential to clarify how species diversity is maintained, currently a central focus in ecology.