2015 National Resources Inventory

The National Resources Inventory (NRI) is a statistical survey of natural resource conditions and trends on non-Federal land in the United States. Non-Federal lands include privately owned lands, tribal and trust lands, and lands controlled by state and local governments.

National Wetlands


Wetlands and Deepwater Habitats on Water Areas and Non-Federal Land
In thousands of acres, with margins of error
Type 1992 1997 2002 2007 2012 2015
Palustrine Wetlands 105,483.9
± 1,531.2
± 1,543.1
± 1,290.0
± 1,289.1
± 1,299.9
± 1,305.6
Estuarine Wetlands 5,275.8
± 194.9
± 192.0
± 374.6
± 372.7
± 377.9
± 377.9
Total Palustrine and Estuarine Wetlands 110,759.7
± 1,561.0
± 1,571.8
± 1,272.3
± 1,272.8
± 1,282.4
± 1,287.7
Lacustrine Aquatic Habitat 25,964.6
± 364.4
± 370.2
± 252.3
± 250.3
± 247.0
± 246.2
Other Aquatic Habitat (*) 22,828.7
± 179.0
± 185.3
± 233.2
± 233.0
± 236.8
± 238.6
Total Aquatic Habitat 48,793.3
± 415.3
± 412.3
± 274.6
± 268.8
± 274.5
± 273.0
Total Wetlands and Aquatic Habitat 159,553.0
± 1,503.4
± 1,515.2
± 1,200.8
± 1,198.8
± 1,202.5
± 1,207.4
Wetlands & Deepwater Habitats pie chart, see Wetlands and Deepwater Habitats on Water Areas and Non-Federal Land table for data values
• (*) includes Estuarine deepwater, and all Riverine and Marine systems.

Palustrine and Estuarine Wetlands on Water Areas and Non-Federal Land,
by Land Cover/Use
In thousands of acres, with margins of error
Land Cover/Use 1992 1997 2002 2007 2012 2015
Cropland, Pastureland, and CRP Land 18,425.3
± 516.2
± 521.6
± 833.4
± 874.4
± 875.0
± 887.6
Rangeland 8,281.1
± 438.2
± 448.2
± 679.4
± 666.5
± 648.6
± 643.8
Forest Land 65,764.9
± 1,172.7
± 1,205.7
± 1,270.5
± 1,307.1
± 1,336.1
± 1,337.0
Other Rural Land 14,299.2
± 551.8
± 547.4
± 604.8
± 612.9
± 625.8
± 617.0
Developed Land 957.8
± 65.0
± 79.3
± 174.5
± 174.4
± 175.0
± 174.3
Water Areas 3,031.4
± 64.7
± 73.9
± 118.0
± 129.0
± 121.0
± 119.8
Total 110,759.7
± 1,561.0
± 1,571.8
± 1,272.3
± 1,272.8
± 1,282.4
± 1,287.7
Palustrine & Estuarine Wetlands pie chart, see Palustrine and Estuarine Wetlands on Water Areas and Non-Federal Land table for data values
• CRP (Conservation Reserve Program) land was not implemented until 1985.
• Cropland includes cultivated and noncultivated cropland.

About the Data

Estimates presented here are based upon the latest information from the National Resources Inventory (NRI). The NRI is a longitudinal sample survey based upon scientific statistical principles and procedures. It is conducted by the U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS), in cooperation with Iowa State University’s Center for Survey Statistics and Methodology.

These results are based upon the 2015 NRI, which provides nationally consistent data for the 30-year period 1982–2015. Current estimates cover the contiguous 48 States, Hawaii, and the Caribbean Area.

Release of NRI results is guided by NRCS policy and is in accordance with OMB and USDA Quality of Information Guidelines developed in 2001. NRCS is releasing NRI estimates only when they meet statistical standards and are scientifically credible in accordance with these policies; also, measures of statistical uncertainty are provided for all 2015 NRI estimates released to the public.

NRI classification of wetlands is slightly different than that used by the Fish & Wildlife Service (FWS) in their statistically based Wetlands Status and Trends study. The NRI and the FWS inventory have different legislative mandates; sampling methodology, inventory protocols, data handling, and analysis routines have evolved independently over the past two decades, even though both survey programs use the hierarchical Cowardin classification system. Recent collaborative efforts have resulted in enhanced classifications for both programs, but wetlands data collected by the two agencies are currently neither comparable nor interchangeable. The NRI multiresource approach is beneficial to USDA analysts and others who examine conservation and agrienvironmental issues. Results from the FWS study are beneficial to analysts in the Department of the Interior and others.

Irrespective of the scale of analysis, margins of error must be considered. Margins of error (at the 95 percent confidence level) are presented for all NRI estimates. Note that estimates of change between two points in time will be less precise (relatively) than estimates for a single inventory year because the changes will be occurring on a smaller fraction of the landscape.


  • Deepwater habitat. Any open water area in which the mean water depth exceeds 6.6 feet in nontidal areas or at mean low water in freshwater tidal areas, or is covered by water during extreme low water at spring tides in salt and brackish tidal areas, or covers the deepest emerging vegetation, whichever is deeper.
  • Wetlands. Lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. For purposes of this classification wetlands must have one or more of the following three attributes: (1) at least periodically, the land supports predominantly hydrophytes; (2) the substrate is predominantly undrained hydric soil; and (3) the substrate is nonsoil and is saturated with water or covered by shallow water at some time during the growing season of each year (Cowardin, et al. 1979).
  • Cowardin system. A classification system of wetlands and deepwater habitats of the United States, officially adopted by the U.S. Fish and Wildlife Service (FWS) used to develop wetland data bases. The five major systems are Estuarine, Lacustrine, Marine, Palustrine, and Riverine (Cowardin, et al. 1979).
    • Palustrine Wetland. Wetlands occurring in the Palustrine System, one of five systems in the classification of wetlands and deepwater habitats (Cowardin et al. 1979). Palustrine wetlands include all nontidal wetlands dominated by trees, shrubs, persistent emergent plants, or emergent mosses or lichens, as well as small, shallow open water ponds or potholes. Palustrine wetlands are often called swamps, marshes, potholes, bogs, or fens.
    • Estuarine Wetland. Wetlands occurring in the Estuarine System, one of five systems in the classification of wetlands and deepwater habitats (Cowardin et al. 1979). Estuarine wetlands are tidal wetlands that are usually semienclosed by land but have open, partly obstructed or sporadic access to the open ocean, and in which ocean water is at least occasionally diluted by freshwater runoff from the land. The most common example is where a river flows into the ocean.
    • Lacustrine System. Wetlands and deepwater habitats occurring in the Lacustrine System, one of five systems in the classification of wetlands and deepwater habitats (Cowardin et al. 1979). The Lacustrine System includes wetlands and deepwater habitats with all of the following characteristics: (1) situated in a topographic depression or a dammed river channel; (2) lacking trees, shrubs, persistent emergent plants, emergent mosses or lichens with greater than 30% areal coverage; and (3) total area exceeding 20 acres. Similar habitats totaling less than 20 acres are included if an active wave-formed or bedrock shoreline feature makes up all or part of the boundary, or if the water depth in the deepest part of the basin exceeds 6.6 feet at low water.
    • Marine System. The open ocean overlying the continental shelf and its associated high energy coastline. Marine habitats are exposed to the waves and currents of the open ocean and the water regimes are determined primarily by the ebb and flow of oceanic tides. One of the five systems in the classification of wetlands and deepwater habitats (Cowardin et al. 1979).
    • Riverine System. All wetland and deepwater habitats contained within a channel, with two exceptions (1) wetlands dominated by trees, shrubs, persistent emergents, emergent mosses, or lichens; and (2) habitats with water containing ocean derived salts. One of the five systems in the classification of wetlands and deepwater habitats (Cowardin et al. 1979).
  • Land cover/use. A term that includes categories of land cover and categories of land use. Land cover is the vegetation or other kind of material that covers the land surface. Land use is the purpose of human activity on the land; it is usually, but not always, related to land cover. The NRI uses the term land cover/use to identify categories that account for all the surface area of the United States.
    • Cropland. A land cover/use category that includes areas used for the production of adapted crops for harvest. Two subcategories of cropland are recognized: cultivated and noncultivated. Cultivated cropland comprises land in row crops or close-grown crops and also other cultivated cropland, for example, hayland or pastureland that is in a rotation with row or close-grown crops. Noncultivated cropland includes permanent hayland and horticultural cropland.
    • Conservation Reserve Program (CRP) land. For NRI, only acres that have been enrolled in CRP general sign-up are included in the CRP land cover/use category. It does not include acres enrolled under CRP continuous sign-up.
    • Developed land. A combination of land cover/use categories, large urban and built-up areas, small built-up areas, and rural transportation land.
      • Urban and built-up areas. A land cover/use category consisting of residential, industrial, commercial, and institutional land; construction sites; public administrative sites; railroad yards; cemeteries; airports; golf courses; sanitary landfills; sewage treatment plants; water control structures and spillways; other land used for such purposes; small parks (less than 10 acres) within urban and built-up areas; and highways, railroads, and other transportation facilities if they are surrounded by urban areas. Also included are tracts of less than 10 acres that do not meet the above definition but are completely surrounded by urban and built-up land. Two size categories are recognized in the NRI: areas of 0.25 acre to 10 acres, and areas of at least 10 acres.
      • Large urban and built-up areas. A land cover/use category composed of developed tracts of at least 10 acres—meeting the definition of urban and built-up areas.
      • Small built-up areas. A land cover/use category consisting of developed land units of 0.25 to 10 acres, which meet the definition of urban and built-up areas.
      • Rural transportation land. A land cover/use category which consists of all highways, roads, railroads and associated right-of-ways outside urban and built-up areas; also includes private roads to farmsteads or ranch headquarters, logging roads, and other private roads (field lanes are not included).
    • Forest land. A land cover/use category that is at least 10 percent stocked by single-stemmed woody species of any size that will be at least 4 meters (13 feet) tall at maturity. Also included is land bearing evidence of natural regeneration of tree cover (cut over forest or abandoned farmland) and not currently developed for nonforest use. Ten percent stocked, when viewed from a vertical direction, equates to an areal canopy cover of leaves and branches of 25 percent or greater. The minimum area for classification as forest land is 1 acre, and the area must be at least 100 feet wide.
    • Pastureland. A land cover/use category of land managed primarily for the production of introduced forage plants for livestock grazing. Pastureland cover may consist of a single species in a pure stand, a grass mixture, or a grass-legume mixture. Management usually consists of cultural treatments: fertilization, weed control, reseeding or renovation, and control of grazing. For the NRI, includes land that has a vegetative cover of grasses, legumes, and/or forbs, regardless of whether or not it is being grazed by livestock.
    • Rangeland. A land cover/use category on which the climax or potential plant cover is composed principally of native grasses, grasslike plants, forbs or shrubs suitable for grazing and browsing, and introduced forage species that are managed like rangeland. This would include areas where introduced hardy and persistent grasses, such as crested wheatgrass, are planted and such practices as deferred grazing, burning, chaining, and rotational grazing are used, with little or no chemicals or fertilizer being applied. Grasslands, savannas, many wetlands, some deserts, and tundra are considered to be rangeland. Certain communities of low forbs and shrubs, such as mesquite, chaparral, mountain shrub, and pinyon-juniper, are also included as rangeland.
    • Other rural land. A land cover/use category that includes farmsteads and other farm structures, field windbreaks, barren land, and marshland.
    • Water areas. A land cover/use category comprising water bodies and streams that are permanent open water.
  • Federal land. A land ownership category designating land that is owned by the Federal Government. It does not include, for example, trust lands administered by the Bureau of Indian Affairs or Tennessee Valley Authority (TVA) land. No data are collected for any year that land is in this ownership.
  • Margins of Error. Margins of error are reported for each NRI estimate. The margin of error is used to construct the 95 percent confidence interval for the estimate. The lower bound of the interval is obtained by subtracting the margin of error from the estimate; the upper bound is obtained by adding the margin of error to the estimate. Confidence intervals can be created for various levels of significance which is a measure of how certain we are that the interval contains the true value we are estimating. A 95 percent confidence interval means that in repeated samples from the same population, 95 percent of the time the true underlying population parameter will be contained within the lower and upper bounds of the interval.

For more definitions see the full 2015 NRI Glossary.

More Information

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Citation for this website:
U.S. Department of Agriculture. 2015.
2015 National Resources Inventory.
Natural Resources Conservation Service, Washington, DC. 31 October 2018 *

*[use date the website was accessed]