Most young, growing forests accumulate carbon at a relatively high rate compared to more mature forests. The rates of net carbon accumulation change with stand age as do important influences affecting carbon change. Individual tree growth rates become less important and processes such as mortality, disturbance, or management play larger roles in determining trends in carbon stocks over time. We characterize carbon stocks at age intervals by region and identify relative importance of these processes on determining changes in net stock change over time. Our approach utilizes the extensive forest inventory data of the US Forest Service Forest Inventory and Analysis Program (FIA), which maintains a continuous program of annual forest measurements on permanent inventory plots across the United States. Plots are remeasured on time intervals ranging from 5-10 years; the longer remeasurement interval is generally used in western states. Our objectives include summarizing the current state of carbon storage and accumulation in live and dead trees and investigating differences by geographic region, stand age class, and hardwood/softwood forest types.
Results/Conclusions
Preliminary analysis reveals the highest average carbon density for aboveground live trees is found on the western side of the Cascade Mountains in the Pacific Northwest, with an average value of 168 tonnes/hectare (t/ha) while the lowest values are in the forests of the southern Rocky Mountains and central United States, at 21.8 and 21.2 t/ha, respectively. The amount of carbon in standing dead trees is also highest in the western portion of the Pacific Northwest (8.8 t/ha), while values below 1.5 t/ha are found in Great Plains, Northeast, and Southeast forestlands. Differences in aboveground live tree carbon stocks are apparent between hardwood and softwood types but do not follow a consistent pattern among regions; mean values are 55.4 t/ha for hardwoods and 66.9 t/ha for softwood types. This difference is more pronounced in western states, where average live and dead tree carbon is higher in softwood stands; 29.9 and 7.7 t/ha, respectively. Ongoing work includes estimating rates of change in carbon accumulation over time, assessing regional differences, and examining relative influence of ecological processes. This information, in turn, contributes to predictive models for management and planning.