Growth enhancement due to global atmospheric change as predicted by terrestrial ecosystem models: consistent with US forest inventory data

Small reported growth enhancement factors based on analyses of forest inventory data from the eastern USA (Caspersen et al. 2000, Science, 290, 1148-1151) have been interpreted as evidence against CO2 fertilization in natural forests. We show to the contrary that growth enhancement in response to rising CO2, as found in ecosystems with experimental CO2 enrichment and implemented in terrestrial ecosystem models, is consistent with the data that have been presented within their uncertainties. Comparing forest inventory data with results of an empirical model of age-dependent biomass accumulation, we find that growth enhancement of plausible magnitude could not be detected in these data, even if it were present. Although forest regrowth due to land-use change is recognized as an important cause of carbon uptake by eastern US forests, forest inventory data do not provide a basis for eliminating environmentally induced growth enhancement as a substantial contribution to the global terrestrial carbon sink.