Background/Question/Methods   Most forests of the world are recovering from a past disturbance. For the U.S. it is estimated that about half of the forest area, or 152 million ha, is disturbed each decade, but this estimate includes a wider range of disturbance types such as timber harvesting and grazing which affect more area than natural disturbances.  In Canada, wildfires were the largest disturbance type in the 20^th century, affecting an average of 2.6 million ha per year in the last two decades. Insect pests are also significant and likely to increase in the future according to model simulations. In this study, we developed the first continental forest age map of the U.S. and Canada by combining forest inventory data, historical fire data, and Landsat and MODIS satellite datasets.

Results/Conclusions We discuss the legacy effect of forest age classes that represent disturbance history and their impact on forest carbon dynamics. By combining geographic information about forest age, carbon dynamics by forest type and age distribution statistics, we estimate the net CO₂ uptake by forests and effects of forest age-classes on current and potential carbon sequestration. We also discuss the importance of integrating the legacy effects of forest age structure in terrestrial carbon models for reducing uncertainty in model prediction, and the potential for increasing forest carbon sinks by managing for the forest age structure that is optimal for offsetting fossil fuel emissions.