Carbon is accumulating in the trees of the US, thereby reducing further accumulation of CO2 to the atmosphere. Whether this accumulation will continue is uncertain, however, because it is not known how much of it is caused by enhanced rates of growth from environmental change (suggesting an increased carbon storage in the future), and how much of it is attributable simply to regrowth following earlier disturbances (suggesting a diminished accumulation in the future). This work seeks to determine the relative contributions of enhanced growth and regrowth to carbon accumulation in the forests of the Northeast. The question will be tackled from three directions: by analyzing the large but previously inaccessible data sets of the US Forest Inventory and Analysis (FIA); by comparison of these FIA data to model simulations of a forest carbon model (to test the hypothesis of enhanced growth); and by reanalyzing historical patterns of land use, management and disturbance (to test the regrowth hypothesis). The work addresses one of the primary goals of the US Climate Change Science Program to determine the magnitude and mechanisms for the accumulation of carbon. The work will also make accessible to the public the 50-year record of tree growth in the Northeast.