Smith, James (USDA Forest Service, Northeastern Research Station, PO Box 640, Durham, NH, 03824; Phone: 603-868-7663; Email: email@example.com)
Forest Carbon Growth and Yield Tables and Uncertainty for U.S. Forest Types
J.E. Smith *, L.S. Heath
We have developed a set of forest carbon growth and yield tables useful as default estimators of the quantity of carbon sequestered in forest stands throughout the U.S. These tables are part of the USDA Forest Service forestry section of the 1605(b) voluntary carbon emissions and sequestration reporting program developed with the U.S. Department of Energy. A purpose of this program is to encourage reduction of the net release of greenhouse gasses to the atmosphere. To report forestry activities, a system to estimate the quantity of carbon sequestered in forest stands and harvested wood products throughout the United States is needed. The system must be accurate, relatively easy to use, credible, and economical. The tables were developed in response to these criteria; they provide default estimates for carbon sequestration projects in situations where more locally specific models or data are unavailable. Tables, representing stand-level merchantable volume and various carbon pools as a function of stand age, were developed for 70 forest types defined within 10 regions of the U.S. based on published models and data, including forest inventory data. Estimates reflect regional averages such as the relatively rapid accumulation in Southern pine plantations (up to 160 tons per hectare of carbon in trees by 25 years) or the large carbon pools in Douglas-fir in the Pacific Northwest (up to 400 tons per hectare of carbon in trees by 75 years). Separate equations were developed for afforestation and reforestation. Forest carbon pools include live trees, standing dead trees, understory, down dead wood, forest floor, and soil organic carbon. Carbon stock estimates are spatially heterogeneous in most forests. Much of the variability can be attributed to influences on stand growth and development such as site characteristics, weather, disturbances, or management practices. The tables are representative of regional averages. Therefore, the uncertainly in applying them to individual stands is partly attributable to forest heterogeneity and partly a reflection of uncertainty in the specific carbon estimators. We develop estimates of uncertainty in the specific carbon density estimators and apply these to both the carbon tables and stand-level inventory data to identify separate components of estimator-based uncertainty and variability in the application of the tables. Independent data sources are used to refine uncertainty estimates.