Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Data

Data Collection Methodology: The USDA Forest Service’s Forest Inventory and Analysis (FIA) program authority is mandated under the Forest and Rangeland Renewable Resources Research Act of 1978 (PL 95–307). Since the late 1940s, FIA has used a two-phase sample (generally, double sampling for stratification) to collect information on the nation’s forests. Phase one establishes a large number of samples (more than 4 million, roughly every 0.6 miles). These are selected using aerial photographs or other remote-sensing images, which are then interpreted for various forest attributes. Phase two establishes a subset of approximately 450,000 phase-one points (roughly every 3 miles) for ground sampling. About 125,000 of these samples are permanently established on forest land. The forest characteristics measured include ownership, protection status, species composition, stand age and structure, tree growth, occurrences of mortality and removals, tree biomass, incidences of pathogens, natural and human-caused disturbances, and soil descriptors.

Forest land is any land that is at least 10% stocked by forest trees of any size, including land that formerly had such tree cover and that will be naturally or artificially regenerated. The minimum area for classification of forest land is 1 acre. For the forest area and ownership indicator, public forests include those owned by federal, state, and local governments, as well as other public entities such as the Tennessee Valley Authority. Private lands include those owned by individuals, corporations, no-governmental organizations, and tribes. The Forest Service’s FIA program derived estimates of historic forest area from a wide variety of sources. For example, the sources included forestclearing data collected during the 1870 and later decennial censuses, limited state and regional surveys, and the expert opinion of resource professionals.

Data Manipulation: Raw data from the 125,000 field samples are processed and merged with information from the remot-esensing phase of the sampling procedure to provide statistically reliable estimates of area and ownership.

Data Quality/Caveats: FIA surveys provide forest area data with a reliability of ±3–10% per 1 million acres (67% confidence limit). This standard applies to all data reported for 1953 and later. Regional totals generally have errors of less than ±2%. No error estimate is provided for data from before 1953. Note also that data collected before 1953 come from a wide variety of sources (see above).

Data Access: All data are available free of charge except for products that require special processing or shipping fees. Electronic databases are unavailable at the national level prior to 1987, and most regional data from before 1977 are not available electronically. Forest statistics, online databases, and a map of U.S. forest distributions are on the Web at http://fia.fs.fed.us. The data provided here through 1997 also are available in Smith et al. (2001).

2003 Web Site Update: Data for 2002 were added in this update. Data were acquired from the Forest Service and are available on the Web at http://fia.fs.fed.us.

References

Smith, W.B., J. Vissage,D. Darr, and R. Sheffield. 2001. Forest statistics of the United States, 1997. Gen. Tech. Rep. NC-219. St. Paul, MN: U.S. Department of Agriculture, Forest Service. 191p.