The overall objective of the carbon dioxide effects research program at the University of Michigan Biological Station is to quantify the carbon dynamics of northern hardwood forests and to predict the response of these forests to changing environmental conditions in the future, particularly to increases in the mole fraction of CO2 in the atmosphere. Studies of tree physiological responses and carbon fluxes in relation to environmental factors are reported here. All studies were made in the field in the successional forests of northern lower Michigan.