Vegetation Classification and Mapping Project Report - USGS

USGS-NPS Vegetation Mapping Program
Colonial National Historical Park
Small-Stream Floodplain Forest is a relatively common association (G4), but high quality,
undisturbed examples are rare. It is widespread from the Coastal Plain of Maryland and Virginia
through the Piedmont of Virginia and North Carolina to the Cumberland Plateau. Coastal Plain /
Piedmont Small-Stream Floodplain Forest was mapped in four of the seven parks included in this
study. Along Beaverdam Creek in Yorktown Battlefield, Coastal Plain / Piedmont Small-Stream
Floodplain Forest grades into Coastal Plain / Piedmont Floodplain Swamp (Green Ash – Red
Maple Type), which is found on poorly drained portions of the floodplain, with pronounced
seasonal flooding. Coastal Plain / Piedmont Floodplain Swamp (Green Ash – Red Maple Type)
typically has high cover of green ash (Fraxinus pennsylvanica) and/or red maple (Acer rubrum)
and more cover by species favoring longer hydroperiods and poorly drained, mucky soils such as
lizard's tail (Saururus cernuus) and threeway sedge (Dulichium arundinaceum). Much of the
area mapped as Coastal Plain / Piedmont Floodplain Swamp (Green Ash – Red Maple Type) has
been altered by beaver activity, which threatens to convert this area to Semipermanent
Impoundment. Coastal Plain / Piedmont Floodplain Swamp (Green Ash – Red Maple Type) is
known from the Chesapeake Bay region from Virginia north through Deleware, and into the
Coastal Plain of New Jersey. Colonial National Historical Park is the only park in this study
where this association was documented.
The four remaining nontidal wetland map classes are considered non-alluvial wetlands. Non-
Riverine Saturated Forest is mapped as 53.4 ha (132.0 ac) on a nearly flat, broad stream terrace
in the vicinity of Powhatan Creek and Green Spring. This wetland forest is distinguished by its
landscape position in an inactive floodplain and the high frequency of hydric oaks and other
characteristic herbaceous species. Most of the area mapped as Non-Riverine Saturated Forest at
Green Spring is regeneration of sweetgum (Liquidambar styraciflua) codominating with loblolly
pine (Pinus taeda), but there are a few patches of more mature hydric oaks scattered throughout
the stand, representing the historic condition of the forest. Non-Riverine Saturated Forest is
restricted to extensive, flat terraces and very wide, ancient floodplains that are no longer subject
to alluvial processes, but are saturated or seasonally flooded due to a high water table. These
specialized wetland habitats were probably never common on the landscape, and mature,
undisturbed examples of this globally rare association are quite rare. Non-Riverine Saturated
Forest is only known from about 25 sites in 13 counties in Virginia and it may range into
Maryland. Much of the suitable habitat for the association has been lost to agriculture,
hydrologic alterations, and conversion of hardwood forests to silvicultural pine plantations.
The non-alluvial wetland Coastal Plain Calcareous Seepage Swamp forms over moderately to
highly base-rich substrates in the bottoms of ravines that have downcut into Tertiary shell
deposits or limesands. The association is endemic to the central Virginia Coastal Plain and is
known only from ravines within the James and York River drainages in James City, Surry, and
York counties, Virginia. In Colonial National Historical Park, this vegetation covers 30.9 ha
(76.3 ac) and is mapped at Swanns Point, along Colonial Parkway near Papermill Creek, and in
various ravine bottoms in the vicinity of Yorktown Battlefield. Coastal Plain Calcareous
Seepage Swamp is easily recognized in the field by its occurrence in narrow ravine bottoms and
the characteristic canopy and herbaceous flora. The examples mapped at Swanns Point represent
a unique variant of this association that is codominated by bald cypress (Taxodium distichum).
High-quality examples of Coastal Plain Calcareous Seepage Swamp are uncommon throughout
the range of this globally rare association. Areas of Coastal Plain Calcareous Seepage Swamp
are relatively small in size and threatened by beaver activities, agricultural pollutants, hydrologic
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