Old-growth forests provide an estimate of the maximum amount of carbon that a forest can store. These benchmark values can be used when comparing forests of the same type to gauge the potential for storing additional carbon (and reducing the amount of carbon dioxide in the atmosphere). Forest Service scientists, working with National Forest Systems partners, measured carbon in old-growth hardwood and softwood forests in Maine, Vermont, and New Hampshire. On average, old-growth hardwood and softwood forests stored 216 and 267 metric tons of carbon/ha, respectively. They found that the main difference was forest floor carbon: higher in softwoods (52) than in hardwoods (18 metric tons/ha). Carbon stored in live trees was similar for hardwoods (116) and softwoods (125 metric tons per 2.47 acres). The researchers compared carbon stocks in the old-growth hardwood sites to those in mature second growth hardwood forests (80 to 120 years old) and found that live-tree carbon in second-growth forests was similar to the old-growth, averaging 108 metric tons per 2.47 acres. The greatest difference between the old-growth and second-growth forests was forest floor carbon, which was 49 percent lower in second-growth sites. Their findings highlight the resilience of forests and the importance of protecting the forest floor during management activities.