A key issue to resolve is whether soil carbon stocks will accumulate indefinitely or reach some steady state in a matter of decades or centuries, depending on the forest type and climatic conditions. We also need to improve our understanding of the linkages between biodiversity structure and ecosystem functions, particularly how these interact with the carbon and nitrogen cycles and the relationships between these biogeochemical cycles. A challenging issue beyond the natural sciences is whether and how the various goods of biodiversity, carbon sequestration, timber production, recreation and other amenity values of forests may be handled and arbitrated within a common framework of ecosystem services.