My research focuses on plant and ecosystem responses to global change, including rising atmospheric carbon dioxide, altered climatic drivers such as temperature and precipitation, and changes in land use and community composition. The future trajectory of the North American carbon sink remains highly uncertain as mixed deciduous forests of the U.S. Midwest and east transition from early to mid and late successional communities. Following heavy disturbance in the 19th and early 20th centuries, dominant early successional canopy species are reaching maturity and beginning to senesce, giving way to a canopy that is more species diverse and structurally heterogeneous. Large-scale mortality is also forcing redistribution of carbon and nitrogen, with the consequences for forest carbon cycling processes largely unknown. Our research combines above-canopy eddy covariance flux measurements, ground-based near surface remote sensing, chemical analysis of canopy foliage, and biometric carbon storage accounting methods to evaluate the effects of changing canopy structural and biological complexity on forest carbon storage potential. We have identified mechanisms supporting sustained high carbon storage in aging and old growth mixed deciduous forests in the upper Great Lakes region. Our results contribute to continental and global scale modeling efforts to improve the quantitative certainty of predictions of future terrestrial carbon storage, and to advance the formulation of forest management prescriptions for enhancing carbon sequestration in older forests.