Maintenance and Review of the National Wetland Classification Standard

Document number


Maintenance Authority



The proposal objective is to produce a newly edited and updated version of the FGDC-approved wetlands classification standard, Classification of Wetlands and Deepwater Habitats of the United States (Cowardin et al.). The standard will be formatted to be consistent with recently endorsed standards with the text edited, refined, clarified, and rewritten as necessary. There have been advances in our scientific understanding. For example, the concept of what should be considered to be soil has been expanded. Areas that were considered to be nonsoil or hydric substrates now fall under the definition of soil. This doesn’t change the concept of wetlands but it does change examples and wording of the existing text. The National Wetlands Inventory staff has tested the standard and has operationally refined it through extensive mapping. Changes, which support the classification standard, were identified during the development of the Wetlands Mapping Standard, FGDC-STD-015 -2009, endorsed by the Federal Geographic Data Committee in July 2009. All the refinements that were endorsed as part of the mapping standard development and supported by the National Wetlands Inventory’s Data Collection Requirements and Procedures for Mapping Wetland, Deepwater, and Related Habitats of the United States will be incorporated into the revised classification standard.

This revised standard will be used by the U.S. Fish and Wildlife Service’s (Service) National Wetlands Inventory (NWI) to complement the Wetland Mapping Standard for entering federally-funded and outside contributed standards-compliant wetlands geospatial data into the Wetlands Layer of the National Spatial Data Infrastructure (NSDI).


Topics for Review and Revisions:

A preliminary document has been developed by the workgroup chairs to identify those parts of the Classification Standard that are expected to be revised. This document will serve as the roadmap for the standard review discussions.

Definition: There will be no changes to the definition of wetlands or regulatory jurisdiction.  The definition of wetlands that is included in the classification standard defines the biological limit of wetlands. Federal, state, and local regulatory agencies with jurisdiction over wetlands may define and describe wetlands in a different manner than the wetlands defined in the classification standard and described in the mapping standard. There is no attempt to define the limits of proprietary jurisdiction of any Federal, state, or local government or to establish the geographical scope of the regulatory programs of government agencies. Persons intending to engage in activities involving modifications within or adjacent to wetland areas should seek the advice of appropriate federal, state, or local agencies concerning specified agency regulatory programs and proprietary jurisdictions that may affect such activities.

Hierarchical System: The structure of this classification is hierarchical, progressing from Systems and Subsystems, at the most general levels, to Classes, Subclasses, and Dominance Types. Modifiers for water regime, water chemistry, and soils are applied to Classes, Subclasses, and Dominance Types. Special modifiers describe wetlands and deepwater habitats that have been either created or highly modified by man or beavers.

There will not be any changes in the hierarchical structure of the classification system nor changes to the top three levels of the hierarchy including System, Subsystem, and Class. These levels have proven to be resilient through thirty years of mapping. This means that there will not be any changes in the categories of wetlands that have been used to produce in the four reports to Congress of the status and trends in the conterminous United States. These reports cover the status and trends of wetlands from the mid-1950s. The fifth report is due by the end of calendar year 2010. This continuity will also provide EPA’s National Wetland Condition Assessment wetlands categories that have been monitored for 60 years.

Subclasses: Each Class is further subdivided into Subclasses; vegetated subclasses are described in terms of life form and substrate subclasses in terms of composition. The Forested Wetland Class is divided into the Subclasses Broad-leaved Deciduous, Needle-leaved Deciduous, Broad-leaved Evergreen, Needle-leaved Evergreen, and Dead. The Unconsolidated Bottom Class is divided into the subclasses Cobble-Gravel, Sand, Mud, and Organic. It was anticipated that as the wetlands and deepwater habitats classification system was used the need for additional Subclasses would become apparent. We expect that Subclasses will be added during this maintenance cycle.

Dominance Types: Subclasses can be further defined by Dominance Types. Dominance Types are determined on the basis of dominant plant species, dominant sedentary or sessile animal species, or dominant plant and animal species. A dominant plant species has traditionally meant one that has control over the community, and this plant is also usually the predominant species. The Dominance Type is most important to users interested in detailed regional studies. The wetlands classification standard only provides examples for the vast number of Dominance Types that occur. Over the years, it has been assumed that Dominance Types could be extracted from other datasets through the use of GIS. This topic is open for discussion and modification or expansion.

Modifiers: To fully describe wetlands and deepwater habitats modifiers for water regime, salinity, pH, soil, and special modifiers were specifically developed or adapted from existing classifications systems. Changes that were endorsed as part of the mapping standard and supported by the data collection procedures and techniques will be added. Clarifications, editorial and technical changes will be made as necessary.

Regionalizations: In the classification standard, a given taxon has no particular regional alliance; its representatives may be found in one or many parts of the United States. The classification standard will continue to use Bailey Ecoregions for inland areas but we will look at modifying the Marine and Estuarine provinces to coincide with those endorsed as a FGDC standard through the Coastal and Marine Ecological Classification system.

Plates: The plates at the end of the standard illustrate examples of wetland classification and will be updated with robust images gathered from the wetlands science community. The Wetlands Classification Image Gallery has been created to facilitate submission and retrieval of well-documented images to support widespread use of the Cowardin Classification System.

Other: Sections on use of the Classifications System, Relationship to Other Wetland Classifications, etc. will be rewritten based on thirty years of mapping and data use. Appendices will be modified, refined, added or dropped as necessary.

Sponsored by

FGDC Wetlands Subcommittee 

Project History

(in chronological order)

2010-02-23 FGDC Standards WG approves project proposal