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published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution.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 Indicator

Definitions for the terms “growth,” “harvest,” and “timberlands,” as used in this indicator, are those used by the USDA Forest Service. Growth is the net annual increase in the volume of living tree stems between inventories after accounting for effects of mortality but before accounting for the effects of harvest. Harvest is a measure of the average annual volume of living trees harvested between inventories. Timberland is the subset of forest land on which harvesting is not prohibited by law and potential wood growth rates are greater than 20 cubic feet per acre per year. Growth is a rough measure of the rate at which forests are converting solar energy into tree biomass. Comparing growth with harvest is a frequently used method of assessing whether wood harvesting is reducing the volume of tree biomass in a forest.

The Data

The data presented in this indicator are not directly comparable with the data presented in the timber harvest indicator, because the data presented here report only the volume of “growing stock,” an inventory category that excludes certain trees and parts of trees (these data—defined below—are used for both the growth and harvest categories presented here). The harvest data presented in Timber Harvest (p. 130) encompass a broader suite of timber products, including “growing stock” and other harvested materials.

Data Source: Data for this indicator were collected under the USDA Forest Service Forest Inventory and Analysis (FIA) program, which is described on page 239. FIA data are from national compilations of periodic statewide survey data.

Data Quality/Caveats: The data for this indicator are limited to “growing stock” trees. Growing stock is a Forest Service inventory category that includes live trees of commercial species meeting specified standards of quality or vigor. When used in calculating volume, this category includes only trees 5.0 inches d.b.h. (“diameter at breast height” a common measurement of tree size) and larger, and which have no obvious characteristics that would make them unusable for industrial use (e.g., rot, unusual shape). In addition, volume is computed for the central stem from a 1-foot stump to a minimum 4-inch top diameter outside bark, or to the point where the central stem breaks into limbs. Noncommercial species are species that normally do not develop into trees suitable for industrial wood products. Since many forest products are made from trees and parts of trees that are not counted as “growing stock” for this indicator, the amounts and trends shown here may differ from those shown in the harvest and use indicator.

This indicator does not provide data on the species, age, quality, or other attributes of the trees being harvested or of trees whose growth is measured. General trends in growth and harvest in the East and West do not reflect some important trends that are occurring at smaller scales. Factors influencing trends in growth and removals vary substantially among and within regions. Subregions where growth/harvest ratios are similar today may have very different growth/harvest ratios in the future. In the West, growth/harvest ratio on timberland may be a poor indicator of change in forest biomass because timberland accounts for only 40% of total forest area in the region. These data exclude forest areas in parks and wilderness, where timber harvesting is prohibited, as well as slow-growing forests.

Current inventory practices limit the data shown here to the main trunk of trees of a certain size, shape, and species. Therefore, the data presented are not directly comparable with the figures presented for Timber Harvest and Use, which account for products made from all parts of all species of trees. Because this indicator does not include information on growth in slow-growing forests and those in parks and wilderness, which make up 60% of western forests, it may not reflect significant changes in forest growth in that region.

Data Access: see the technical note for Forest Area and Ownership; additional data for this indicator were taken from the publications listed in the references.

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

USDA Forest Service. 1958. Timber resource for America’s future. Forest Resource Report No. 14. Washington, DC.

USDA Forest Service. 1965. Timber trends in the United States. Forest Resource Report No. 17. Washington, DC.

USDA Forest Service. 1982. An analysis of the timber situation in the United States 1952–2030. Forest Resource Report No. 23. Washington, DC.

Waddell, K.L., D.D. Oswald, and D.S. Powell. 1989. Forest Statistics of the United States, 1987. Resource Bulletin PNWRB- 168. Portland, OR: USDA Forest Service