The carbon balance of an old-growth forest: Building across approaches

The carbon budget of the Wind River old-growth forest is being addressed from a variety of perspectives and with a range of approaches. The goal of this comprehensive analysis is developing a thorough, general, and validated understanding of the carbon balance, as well as the processes controlling it. The initial results from studies addressing annual carbon (C) balance with ground-based methods, eddy flux, leaf-based models, and ecosystem models are consistent in some, but not all, respects. Net primary production is 500-600 g C m(-2) y(-1) (5-6 Mg C ha(-1) y(-1)), consistent with estimates based on climate alone. The site appears to be close to carbon equilibrium, as a multiyear average, using ground-based methods but a sink of approximately 150-190 g C m(-2) y(-1) from eddy flux for a single year. An overview of the mechanisms that can drive forest carbon sinks illustrates why methods emphasizing different temporal and spatial scales, as well as different processes, can come to different conclusions, and it highlights opportunities in moving toward a truly integrated approach.