Report on the Environment
What are the trends in land use and their effects on human health and the environment?
The above question pertains to all 'Land Use' Indicators, however, the information on these pages (overview, graphics, references and metadata) relates specifically to "Land Use". Use the right side drop list to view the other related indicators on this question.
Click to enlarge exhibit
Land use is the purpose of human activity on the land. Unlike land cover, land use may not always be visible. For example, a unit of land designated for use as timberland may appear identical to an adjacent unit of protected forestland or, if recently harvested, may appear not to be in forest land cover at all. Land use is generally designated through zoning or regulation and is one of the most obvious effects of human inhabitation of the planet. It can affect both human health and ecological systems, for example by changing the hydrologic characteristics of a watershed, the potential of land to erode, the condition or contiguity of plant and animal habitat, or the spread of vector-borne diseases.
This indicator tracks trends in acreages of major land uses over the 1977-2003 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 of them provides an important piece of the land use picture over time. Definitions for the various land use categories in this indicator can be found in the text box.
The National Resources Inventory (NRI) conducted by the U.S. Department of Agriculture (USDA) Natural Resources Conservation Service 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 and 2002 only. Data on the extent of grass and forested rangeland (typically “unimproved” grazing land) are available from the USDA Economic Research Service (ERS) for 5-year intervals from 1982 through 2002.
The acreage of lands used for growing food and forage crops has declined since 1982, while developed land has increased and timberland has remained approximately constant (Exhibit 4-5). As of 2002-2003, estimates from both the NRI (2003 data) and the NASS (2002 data) indicate that between 368 and 374 million acres were used for food crop production, approximately 16 percent of the U.S. land area. Estimates of pasture or land used to support forage for livestock vary, depending on the definitions. The NRI classifies 117 million acres as pasture, while the NASS classifies about 61 million acres as cropland used for pasture. The NASS classifies more than 395 million additional acres as pasture or rangeland for grazing. The broader ERS estimate of land available for grazing totals about 587 million acres, and includes grassland and other non-forested pasture and range. If forest lands used for grazing are also included, the total ERS estimate for these lands is 721 million acres for 2002. The NASS shows a decrease in the extent of cropland (5 million acres), cropland pasture (6 million acres), and pastureland and rangeland (3 million acres) between 1997 and 2002. The NRI data suggest that these declines are part of a longer trend, with NRI cropland and pasture declining by slightly more than 66 million acres (12 percent) between 1982 and 2003. ERS data also show a downward trend for pasture and rangeland between 1982 and 2002, with the largest decrease being a 24-million-acre (15 percent) decline in forest land used for grazing.
According to the NRI, 5 percent (108.1 million acres) of U.S. land area was considered developed1 as of 2003 (Exhibit 4-5). This represents a gain of 48 percent (35.2 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 504 million acres of U.S. forest land, or 22 percent of the total U.S. land area, qualified as timberland in 2002 (Exhibit 4-5). This total reflects a net gain of about 11 million acres (2 percent) between 1977 and 2002, which the FIA attributes largely to reversion of abandoned lands and reclassification of some National Forest lands to align with classifications used on other land ownerships (Smith et al., 2004).
Land use varies widely by EPA Region (Exhibit 4-6). 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 83 percent of the cropland lost between 1987 and 2003 was in five EPA Regions (Regions 4, 5, 6, 7, and 8) (Exhibit 4-7, panel A). Increases in developed land are responsible for part of this decline; for example, developed land increased by nearly 60 percent from 1987 to 2003 in Region 4 (Exhibit 4-7, panel B). Other factors include the federal Conservation Reserve Program, which has assisted private landowners in converting about 35 million acres of highly erodable cropland to vegetative cover since 1985 (as of 2004) (USDA Farm Service Agency, 2004).[Definitions of Land Use Categories for Exhibits 4-5, 4-6, and 4-7]
- 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 1980 to 2001 for reporting 2002 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 Lubowski et al. (2006). FIA data were obtained from Smith et al. (2004). NASS data were published by the USDA National Agricultural Statistics Service (2004).
Lubowski, R.N., M. Vesterby, S. Bucholtz, A. Baez, and M.J. Roberts. 2006. Major uses of land in the United States, 2002. Economic Information Bulletin No. (EIB-14). U.S. Department of Agriculture, Economic Research Service. http://www.ers.usda.gov/publications/eib14/
Smith, W.B., P.D. Miles, J.S. Vissage, and S.A. Pugh. 2004. Forest resources of the United States, 2002. USDA Forest Service. http://ncrs.fs.fed.us/pubs/gtr/gtr_nc241.pdf
USDA Farm Service Agency (United States Department of Agriculture, Farm Service Agency). 2004. The Conservation Reserve Program: Summary and enrollment statistics, 2004. http://www.fsa.usda.gov/Internet/FSA_File/fy2004.pdf
USDA NASS (United States Department of Agriculture, National Agricultural Statistics Service). 2004. 2002 census of agriculture, United States summary and state data. Report AC-02-A-51. http://www.nass.usda.gov/census/census02/volume1/us/us2appxc.pdf (QA/QC); http://www.nass.usda.gov/census/census02/volume1/USVolume104.pdf
USDA NRCS (United States Department of Agriculture, Natural Resources Conservation Service). 2007. National Resources Inventory, 2003 annual NRI: Land use. http://www.nrcs.usda.gov/technical/nri/2003/nri03landuse-mrb.html
USDA NRCS. 2004. National resources inventory: 2002 annual NRI. http://www.nrcs.usda.gov/technical/NRI/2002/glossary.html
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 Section 4.2 for more information.
|2.||ROE Question(s) This Indicator Helps to Answer|
|This indicator is used to help answer two ROE questions: "What are the trends in land use and their effects on human health and the environment?" and "What are the trends in the extent and distribution of the Nation's ecological systems?"|
This indicator describes the status of, and trends in, various categories of land use in the United States as a whole, and for EPA regions, from 1977 to 2003. This information provides an understanding of how land use is changing in the United States, which can affect both human health and ecological systems.
This indicator is based on four sources of data:
NRI data used in the indicator are from USDA NRCS (2007). The complete files can be obtained on CD from USDA for a processing fee of $50 (see http://www.nrcs.usda.gov/technical/NRI/1997/obtain_data.html). Sources for definitions of NRI land use categories shown in the text of the indicator are from USDA NRCS, 2004.
FIA data were published in Smith et al. (2004). Additional detail can be obtained from the FIA database at http://fia.fs.fed.us/tools-data/.
NASS data were published in the Census of Agriculture (USDA NASS, 2004), available online.
ERS data were obtained from Lubowski et al. (2006), also available online.
The NRI is conducted by the USDA NRCS in cooperation with Iowa State University's Center for Survey Statistics and Methodology. The NRI covers only non-federal land in the United States. Non-federal land refers to a combination of the following land ownership categories: private, municipal, county or parish, state, and Indian tribal and trust lands.
The NRI uses a stratified two-stage unequal probability area sample to ensure that sample sites are located in all counties and parishes of the 50 states and in Puerto Rico, the Virgin Islands, the District of Columbia, and selected portions of the Pacific Basin. (The reports for the 2002 and 2003 Annual NRI, which update all previous inventory years, cover the 48 contiguous states only.) The primary sample unit (PSU) is the area or segment of land from which one or more points are selected. In 1997, data were gathered from approximately 800,000 points in 300,000 PSUs.
The 2003 Annual NRI statistically updates 1997 NRI results with data collected during 2000-2003. The NRI was conducted on a five-year cycle during the period 1982 to 1997, but is now conducted annually. NRI data were collected every five years for 800,000 sample sites; annual NRI data collection occurs at slightly less than 25 percent of these same sample sites.
NRI data release procedures are affected by implementation of an annual data collection approach, because the scale of NRI estimates is affected by these reduced sample sizes. Estimates are being released when they meet statistical standards and are scientifically credible in accordance with NRCS policy, and in accordance with OMB and USDA Quality of Information Guidelines.
Current estimates cover the contiguous 48 states. Future estimates will also cover Hawaii, Alaska, the Caribbean, and selected Pacific Basin islands.
Further details on the current study methodology including sampling and analytical procedures are available on the NRI Web site at http://www.nrcs.usda.gov/technical/NRI/. More specific information about the statistical reliability and methodology of the 1997 NRI is available at http://www.nrcs.usda.gov/technical/NRI/1997/summary_report/appendices1.html.
The forest monitoring component consists of a three stage systematic sample of sites across all forested lands of the U.S. A nationally uniform cell grid is super-imposed over the set of sample locations, in order to provide a uniform basis for determining the annual set of measurement plots. Phase 1 activities (i.e., remote sensing) classify forest based on a photo point that defines land as forested if it has 10 percent or more coverage by forest. Within the approximately 750 million acres of forested land in the United States, there are approximately 125,000 permanent sampling plots for the FIA inventory, or one sampling plot for every 6,000 acres of forest identified by Phase 1 points (evaluated for every 240 acres of land in the United States). An FIA plot consists of a cluster of four circular subplots spaced out in a fixed pattern. The plot is designed to provide a sampling frame for all Phase 2 (i.e., ground plots focusing on timber-related forest and tree information) and Phase 3 (i.e., focusing on ecological and forest health) measurements. With the federal mandate calling for 20 percent of plots for each state to be sampled every year, each plot should be sampled every 5 years. At present, this number is closer to every 6-10 years, based on a 10 percent sampling intensity in western lands and 15 percent in eastern states. A typical plot usually takes a two to three person field crew one full day to complete; although, these numbers vary from state to state. The most recent annual inventory is based on 2002 data.
FIA sampling and data collection fact sheets are available at http://fia.fs.fed.us/library/fact-sheets/.
The 2002 Census of Agriculture used a mailout/mailback survey methodology as the primary method for collecting data, supplemented with follow-ups by mail, telephone, and personal enumeration. Approximately 2.8 million surveys were distributed to farmers and ranchers in all 50 states. In addition, data from the 1997 Census of Agriculture were re-weighted when published as part of the 2002 Census to ensure their comparability to the 2002 data. See the Introduction and Appendix A of the 2002 Census of Agriculture (USDA NASS, 2004).
ERS data are based on various published and unpublished data from many sources, including NRI, NASS, Bureau of Land Management (BLM), U.S. Forestry Service (USFS), and NRCS. Sampling schema vary across these sources. Limited descriptions of ERS data sources and approaches are presented in the publication describing land use trends (Lubowski et al., 2006), but no details on statistical sampling procedures are provided. The Major Land Uses series is the only consistent accounting of all major uses of public and private land in the United States and contains acreage estimates of major uses by region and States for each census of agriculture year from 1945 through 2002 (Lubowski et al., 2006). 50-state totals in all land use categories may appear to change precipitously in 1959, when Alaska and Hawaii obtained statehood (http://www.ers.usda.gov/Data/MajorLandUses/). A detailed description of the ERS methodology for estimating U.S. cropland area can be found in an article from Amber Waves, Volume 2, Issue 5, (November 2004). See http://www.ers.usda.gov/AmberWaves/November04/Indicators/behinddata.htm.
This exhibit shows land use trends in the U.S. from 1977 to 2003. This exhibit is derived from data from the following four sources; no transformations were made to these data:
This exhibit shows land use in the U.S. by EPA Region in 2002-2003. For this exhibit, state level data were aggregated into EPA regions.
This exhibit shows changes in land use in the U.S. by EPA Region from 1977 to 2003. For this exhibit, state level data were aggregated into EPA regions. Percent changes are calculated as follows: reported acreage change for a land use type over the reported interval was divided by the total acreage for that land use type as reported for the earlier year of the interval, by EPA region.
This exhibit is derived from data from the following three sources:
|9.||Quality Assurance and Quality Control|
Appendices of the 1997 NRI (http://www.nrcs.usda.gov/technical/NRI/1997/summary_report/) discuss issues related to reliability, as well as protocols for quality assurance and control. No similar appendix is available for the 2003 NRI.
Quality assurance/quality control procedures are described in the fact sheet found at http://fia.fs.fed.us/library/fact-sheets/data-collections/QA.pdf (2 pp, 174K, About PDF),
See Appendices A and C of the 2002 Census of Agriculture (USDA NASS, 2004)
Elements of QA/QC for ERS land use data are described in Lubowski et al. (2006).
There are no established reference points, thresholds, or ranges of values for this indicator.
|11.||Comparability Over Time and Space|
The NRI approach is consistent over time and space. The 2003 Annual NRI data replace previous annual inventory data for analysis purposes. With each new inventory the estimates for the previous inventory years are recalculated to reflect changes in inventory technologies and protocols. This editing process ensures consistency for trend analysis across all inventory years (1982, 1987, 1992, 1997, 2001, 2002, 2003) (see http://www.nrcs.usda.gov/technical/NRI/archived.html).
The FIA is a nationally consistent inventory program that includes all forested land in the United States (including Alaska and Hawaii), regardless of ownership or availability for forest harvesting. It covers all public and private forest land, including reserved areas, wilderness, National Parks, defense installations, and National Forests.
Data from the 1997 Census of Agriculture were re-weighted when published as part of the 2002 Census to ensure their comparability to the 2002 data. See the Introduction and Appendix A of the 2002 Census of Agriculture (USDA NASS, 2004).
From Lubowski et al. (2006), page iii: "To ensure comparability with earlier estimates in the series, a standardized set of procedures is used (Barnard and Hexem, 1988). Even so, comparability was sometimes hindered by changes in the characteristics of data available over time. This is inevitable because the estimates are not drawn from a single survey but derived by reconciliation of several data sources."
|12.||Sources of Uncertainty|
Content under review.
|13.||Sources of Variability|
Content under review.
No trend analysis has been conducted for this indicator. Because the various datasets are not consistent in terms of periods of data collected, potential trend analysis for the overall indicator is hindered. Inconsistencies in data collection methodologies also pose problems for analysis. It is possible to analyze trends within various subsets of the data, though.
Limitations to this indicator include the following:
Barnard, C., and R. Hexem. 1988. Major statistical series of the U.S. Department of Agriculture: Land values and land use. Agriculture Handbook No. 671, Vol. 6. U.S. Department of Agriculture, Economic Research Service. Washington, DC.
Lubowski, R.N., M. Vesterby, S. Bucholtz, A. Baez, and M.J. Roberts. 2006. Major uses of land in the United States, 2002. Economic Information Bulletin No. (EIB-14). U.S. Department of Agriculture, Economic Research Service. http://www.ers.usda.gov/publications/eib14/ and http://www.ers.usda.gov/data/majorlanduses/.
Smith, W.B., P.D. Miles, J.S. Vissage, and S.A. Pugh. 2004. Forest resources of the United States, 2002. USDA Forest Service. http://ncrs.fs.fed.us/pubs/gtr/gtr_nc241.pdf (146 pp, 5.8MB).
USDA NASS (United States Department of Agriculture, National Agricultural Statistics Service). 2004. 2002 census of agriculture, United States summary and state data. Report AC-02-A-51. http://www.agcensus.usda.gov/Publications/2002/USVolume104.pdf (663 pp, 4.8MB).
USDA NRCS (United States Department of Agriculture, Natural Resources Conservation Service). 2007. National Resources Inventory, 2003 annual NRI: Land use. http://www.nrcs.usda.gov/technical/nri/2003/Landuse-mrb.pdf (20 pp, 812K). See also http://www.nrcs.usda.gov/technical/NRI/.
USDA NRCS. 2004. National Resources Inventory: 2002 and 2003 annual NRI: Glossary of key terms. http://www.nrcs.usda.gov/technical/NRI/2002/glossary.html.