EPA's Report on the Environment: External Review Draft
Forest Extent and Type
Note to reviewers of this draft revised ROE: This indicator reflects data through 2007. EPA anticipates updating this indicator in 2014.
The forests of the U.S. cover extensive lands in both the eastern and western thirds of the country. While the amount of forest land has remained nearly unchanged since the beginning of the 20th century, regional changes both in amount and types of forest cover have occurred as a result of changing patterns of agriculture and development. The distribution of various forest cover types is a critical determinant of the condition of forest ecosystems.
This indicator is based on data from the U.S. Department of Agriculture (USDA) Forest Service Forest Inventory and Analysis (FIA) program. The FIA program, using a statistical survey design and comparable methods across the U.S., collects various data that help assess the extent, type, age, and health of the nation’s forest land. Because the surveys are repeated over time, the FIA data provide an indication of trends in both the extent and composition of forest land. The extent data are collected for all forest lands across the nation, but species composition data over time are only available for timberland as defined by FIA data collection procedures (that is, forests capable of producing at least 20 cubic feet per acre per year of industrial wood and not withdrawn from timber utilization by statute or regulation). Timberland makes up approximately 95 percent of the forest land area in the eastern U.S. and 40 percent of forest land in the western U.S. as of 2007 (Smith et al., 2009). Extent data are collected for individual states, but have been summarized by EPA Region for this indicator.
What the Data Show
Over the last century, forest land nationwide decreased by 2.6 million acres (Exhibit 1). Forest acreage across all 50 states alternately decreased and increased during the reporting period (1907–2007). The largest decrease nationwide occurred between 1953 and 1977, followed by the largest increase between 1977 and 2007. There are variations in trends in forest cover among the different EPA Regions. For example, between 1907 and 2007, forest land declined by roughly 26.2 million acres in Region 6. Over the same period, forest land increased by 13.5 million acres in Region 3.
In addition to changes in the extent of forest, there have been changes in the types of forests over time (Exhibits 2 and 3). The largest changes in the eastern U.S. over the 1953–2007 period occurred in the maple-beech-birch forest type and the oak-hickory forest type, which gained 26.9 million acres and 30.3 million acres, respectively, since 1953. The largest decreases in the East from 1953 to 2007 were seen among the oak-gum cypress and longleaf-slash pine forest types, which decreased by 14.7 million and 14.0 million acres, respectively. In the West, the fir-spruce type and Western hardwood type also have increased by 12.8 million acres and 15.3 million acres, respectively, since 1953. The hemlock-Sitka spruce and ponderosa-Jeffrey pine forest types have decreased by about 15.2 million and 12.3 million acres, respectively. The Western white pine forest type has decreased by 5.3 million acres, or about 96 percent of its 1953 acreage.
Data on extent of forest land have an uncertainty of 3 to 10 percent per million acres for data reported since 1953. In 1998, Congress mandated that the FIA move to annual inventories. While data now are collected more often, fewer data are collected in any given year. Because area estimates now are based on a smaller sample size, the precision of the national estimates may be reduced relative to pre-1998 dates.
Most of the specific data related to species and age classes are only collected on lands classified as timberland and not forest land in general.
- In addition to extent and species class, age class also influences the use of forest land as habitat by different species. Younger and older stands of forest have increased over the past half-decade, while middle-aged stands of more merchantable timber have decreased (Smith et al., 2001, 2004).
This indicator is primarily based on data from the USDA Forest Service Resources Planning Act (RPA) resource tables, which are publicly available at http://fia.fs.fed.us/program-features/rpa/default.asp (USDA Forest Service, 2008). The RPA resource tables provide current and historical data on forest extent and type by state. The data are also published in a USDA Forest Service report (Smith et al., 2009). The 1963 data were obtained from an older USDA Forest Service report (Smith et al., 2001) because these data were excluded from the newer resource tables. Data were originally collected by the USDA Forest Service’s FIA program; original survey data are available from the FIA database (USDA Forest Service, 2009) (http://www.fia.fs.fed.us/tools-data/).
For More Information
- USDA Forest Service: Forest Inventory and Analysis National Program
- This indicator relates to: Extent and Distribution, Land Cover
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