Product Summary - Historic Wetlands Data Layer
The U.S. Fish and Wildlife Service (Service) is the principal Federal
agency that provides information to the public on the extent and status of
the Nation's wetlands and provides stewardship for the wetlands data that
comprise the Wetlands Layer of the National Spatial Data Infrastructure.
In 2006, the Service released a Strategic Habitat
Conservation plan to guide agency resource management
decisions. Strategic Habitat Conservation practices hinge on
integrating biological and geospatial information at the
landscape level to achieve conservation objectives.
Technological advances in geospatial data capture and
management continue to change and improve the way biological
planning, inventory and assessments are conducted.
Geospatial wetland map data combined with other ecological
information are important decision support tools as part of
the Strategic Habitat Conservation approach. The Service’s
habitat conservation actions will increasingly rely on
geospatial habitat and trend information to help guide,
prioritize, and assess species recovery, wildlife resource
management, wetland threats and habitat restoration project
actions. Historical wetlands are areas where there is
evidence a wetland once existed. This information is useful
for a variety of reasons including landscape level planning
and modeling, determining possible wetland reestablishment
opportunities and tracking changes in land use or ecological
Historic Wetlands Data
Historic wetlands have been identified using several
different techniques depending on the availability and type
of information used to locate these areas and user needs.
For example, historical maps often provide information about
past wetland extent or location and can be useful tools to
identify historic wetlands (Figure 1). Similarly, aerial
photographs can provide a historical record of wetland
extent. More recently, the use of some databases (i.e.,
areas mapped as having wetland soil types in the soil
survey) have been used in attempts to identify historic
wetland. All of these methods have limitations in their
ability to locate, identify and quantify historic wetland
In the formulation of this data layer, historic wetlands
are defined as areas where there is evidence that a wetland
once existed. This evidence can be from historical map
information, inventories of past wetland extent or other
information collected that relate directly to data on
wetland filling, drainage or other modifications. Areas not
included as historic wetland include topographic depressions
where there is no evidence that hydrology created wetland
conditions; modeling of potential past wetland extent based
on empirical datasets; or non-geospatial data.
Figure 1. Historic topographic
map information indicates wetland extent (swamp symbology)
along the shoreline of Green Bay, WI
in 1954 (Source: USGS, Topographic 7.5 minute map series,
Green Bay West Quadrangle, 1954).
Identification and Attribution of Historic Wetlands
Historic wetlands have been identified as polygonal
data. No linear features (lines) have been included.
Historic wetland polygons are not classified or attributed
with wetland labels (Figure 2). Since
these features no longer exist, boundary delineations are
considered approximations based on topography, previously
mapped information or indications of historic water levels.
Figure 2. Historic wetland
polygons (shown in blue) are not classified or labeled since
they are historic features. They are displayed here on the
Wetlands Mapper in combination with existing mapped wetlands
(shown in green).
Historic Wetland versus Restorable Wetland
The term “historic wetland” is not synonymous with
“restorable wetland” as used here. Wetland restoration or
reestablishment is dependent on a number of factors
including past land treatments (filling, flooding or land
leveling), current land use and changes in hydrology. Some
recent studies have demonstrated that some wetlands may not
be restorable because of landscape-level changes to
Efforts to reestablish wetlands have been focused on less
intensively developed land (i.e. agricultural lands) or on
undeveloped land. Only rarely have wetlands been
reestablished in intensively developed areas such as shown
in Figure 3.
||Figure 3. Evidence of lost
wetlands (outlined in red) that have been developed
as upland. The opportunity to reestablish wetland
in such areas is improbable, but tracking these land
use changes can be useful for assessing regional
changes in hydrology, and other ecological trends.
Please read the Disclaimer, Data Limitations, Exclusions and Precautions, and the Wetlands Geodatabase User Caution.