EPA's Report on the Environment: External Review Draft
Note to reviewers of this draft revised ROE: This indicator reflects data through 2007. EPA anticipates updating this indicator in 2014.
Land use is the purpose of human activity on the land. Unlike land cover, land use may not always be visible and may not be inferable from land cover. For example, a unit of land designated for use as timberland may appear identical in land cover to an adjacent unit of protected forestland or, if recently harvested, may appear not to be forest land cover at all. Land use is generally designated through zoning or regulation and is one of the most obvious effects of human habitation on the planet. It can affect both human health and ecological systems, for example by changing hydrologic responses in a watershed, contributing to potential erosion, changing the condition or contiguity of plant and animal habitat, and enhancing the spread of vector-borne diseases.
This indicator tracks trends in the acreage of major land uses over the 1977-2007 period using several data sources. These sources do not always cover the same time period, sample the same resource or geography, or use the same definitions, but each provides an important piece of the land use picture over time. See the definitions page for a detailed description of each land use category.
The National Resources Inventory (NRI) conducted by the U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) was used to track trends in “crop and pasture” land (row crop, orchard, and pasture uses) and “developed” land (residential, commercial, industrial, and transportation uses). The NRI developed estimates every 5 years on non-federal lands in the contiguous U.S. between 1977 and 1997, and annual estimates based on a smaller sample size beginning in 2001.
The Forest Inventory and Analysis (FIA) surveys conducted by the USDA Forest Service were used to track trends in forest and timberlands. The FIA surveys include both private and public land in all 50 states. The FIA previously assessed forest and timberland acreage every 10 years, but the data are now updated on a rolling basis using surveys that sample a different portion of FIA sites every year.
The USDA National Agricultural Statistics Service (NASS) Census of Agriculture was used to track trends in the extent of cropland, cropland used only for pasture, pastureland, and rangeland. NASS data are available for 1997, 2002, and 2007 only.
The USDA Economic Research Service (ERS) provides data on the extent of grassland, forested rangeland, and other land uses for 5-year intervals from 1982 through 2007 and for selected prior years.
What the Data Show
The acreage of land used for growing food and forage crops has declined since 1982, while developed land has increased and timberland has remained approximately constant (Exhibit 1). As of 2007, estimates from both the NRI and the NASS indicate that between 357 and 371 million acres were used for food crop production—approximately 16 percent of the 50-state U.S. land area.
Estimates of pasture or land used to support forage for livestock vary, depending on the data source and definitions. The NRI classifies 119 million acres as pasture, while the NASS, following a methodological change between 2002 and 2007, classifies about 36 million acres as cropland used for pasture in 2007. The NASS classifies 409 million additional acres as pasture or rangeland for grazing. The broader ERS estimate of land available for grazing totals about 614 million acres, and includes grassland and other non-forested pasture and range. If forest lands used for grazing and cropland pasture are also included, the total estimate for grazing lands is 777 million acres for 2007, representing 35 percent of U.S. land area.
The NASS shows a decrease in the extent of cropland (8 million acres) between 1997 and 2007. The NRI data suggest that this decline is part of a longer trend, with NRI cropland declining by 63 million acres (15 percent) between 1982 and 2007.
According to the NRI, 5 percent (111.3 million acres) of U.S. land area was considered developed as of 2007 (Exhibit 1) (The land use classification for developed land uses NRI data and is considerably different from the land cover classification for developed land, which uses NLCD data. See the Land Cover indicator for more information.) This represents a gain of 57 percent (40.3 million acres) since 1982. While the amount of developed land is a small fraction of the total, its ecological impact can be disproportionately high relative to other land use types. Paving and the creation of other impervious surfaces can change local hydrology, climate, and carbon cycling, leading to increased surface runoff, pollution, and degradation of wetlands and riparian zones.
Forest lands are managed by a complex array of interests to meet multiple purposes, including providing habitat for a variety of species, recreation, and timber production. While forest is a land cover classification, timberland is a land use classification that reflects forest land 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. Approximately 514 million acres of U.S. forest land, or 22 percent of the total U.S. land area, qualified as timberland in 2007 (Exhibit 1). This total reflects a net gain of about 22 million acres (4 percent) between 1977 and 2007, which the FIA attributes largely to reversion of pasture and other agricultural lands to forest and reclassification of some National Forest lands to align with classifications used on other land ownerships (Smith et al., 2009).
Land use varies widely by EPA Region (Exhibit 2). According to the most recent data for each land use type, Regions 6, 8, and 9 together have more than three-quarters of the nation’s grazing land, while Region 4 has the largest portion of timberland (27 percent of total U.S. timberland).
Trends also vary widely among regions. About 87 percent of the cropland lost in the U.S. between 1987 and 2007 was in five EPA Regions (Regions 4, 5, 6, 7, and 8) (Exhibit 3). Increases in developed land are responsible for part of this decline; for example, developed land increased by nearly 72 percent from 1987 to 2007 in Region 4 (Exhibit 3). Other factors include the federal Conservation Reserve Program, which has assisted private landowners in converting about 27 million acres of highly erodable cropland to vegetative cover since 1985 (as of 2007) (Nickerson et al., 2009).
- Estimates are derived from a variety of inventories and samples, conducted over different time periods and for different purposes. This limits the ability to integrate the data and track changes over time.
- The NRI does not report land use data for Alaska, which encompasses 365 million acres of the 2.3 billion acres nationwide. The NRI also does not provide data on federal lands (representing 20 percent of the contiguous U.S. land and one-third of Alaska). Because federal land is seldom used for agriculture or urban development, and there is relatively little developed or agricultural land in Alaska, the NRI data likely offer a reasonable approximation of national trends in these categories.
- NRI data use three subcategories of types of developed land: large built-up areas, small built-up areas, and rural transportation land. Because ecological effects from developed land depend on the density of development and many other factors, the limited NRI categories are not discriminating enough to support detailed analyses of ecological effects of developed land.
- The FIA data are aggregated from state inventories in many cases, and dates of data collection for these inventories vary by state—for example, ranging from 1985 to 2006 for reporting 2007 estimates.
- Some land uses may be administratively designated but not physically visible (e.g., lands that are reserved for parks or wilderness may appear similar to lands that are managed for natural resources).
- Land use designations are most frequently managed and monitored by local governments, each using different approaches and classifications. This makes national summaries difficult.
- The extent of lands used for energy production, resource extraction, or mining is not known and represents a data gap.
- Lands specifically protected for certain uses such as wilderness or parks have been periodically inventoried for the nation. These statistics are currently not reported in a form that allows comparison with other statistics.
Data were obtained from several original sources and compiled by EPA Region. ERS data were obtained from Nickerson et al. (2011). FIA data were obtained from Smith et al. (2009). NASS data were published by the USDA NASS (2009). NRI data were obtained from USDA NCRS (2009).
For More Information
- USDA Natural Resources Conservation Service's National Resources Inventory
- USDA Forest Service's Forest Inventory and Analysis National Program
- Learn how this indicator fits into a conceptual diagram for: Wetland Loss
- This indicator relates to: Extent and Distribution, Land Use
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