Department of Conservation and Recreation

THE NATURAL COMMUNITIES OF VIRGINIA
CLASSIFICATION OF ECOLOGICAL COMMUNITY GROUPS

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Second Approximation (Version 2.5)
Information current as of February, 2012

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Tidal Oligohaline Marshes

This group contains primarily graminoid-dominated wetlands of slightly brackish zones along tidal rivers and streams of the Coastal Plain. Oligohaline conditions are defined as salt concentrations between 0.5 and 5 ppt, although pulses of higher halinity may occasionally occur. Vegetation in this group occurs from Maine to Georgia. In Virginia, big cordgrass (Spartina cynosuroides) is the most characteristic and abundant species and often forms extensive, tall stands, particularly along edges of the main tidal channels. Associates include a mix of species characteristic of freshwater marshes, such as dotted smartweed (Polygonum punctatum var. punctatum) and arrow-arum (Peltandra virginica), and species more tolerant of higher salinities, such as eastern rose-mallow (Hibiscus moscheutos ssp. moscheutos) and seashore mallow (Kosteletzkya virginica var. virginica). Other species indicative of oligohaline conditions (when occurring in marshes) include halberd-leaved tearthumb (Polygonum arifolium), Walter's barnyard grass (Echinochloa walteri), and swamp dock (Rumex verticillatus). Some oligohaline marshes contain dense colonies of shoreline sedge (Carex hyalinolepis) or, more commonly, narrow-leaved cattail (Typha angustifolia), the latter of which may be increasing in extent as the result of fire exclusion and eutrophication. Diversity generally decreases as halinity increases, but some communities of mixed composition, particularly those of low stature, may support more species than many tidal freshwater marshes.

Dredge spoils and other disturbed areas often support dense, nearly monospecific colonies of common reed (Phragmites australis ssp. australis ); this highly aggressive, invasive subspecies constitutes a serious threat to tidal marshes throughout the Coastal Plain. The diurnally tidal communities in this group are compositionally distinct from the group of more diverse oligohaline marshes in extreme southeastern Virginia that are subject to irregular wind tides.

References: Coulling (2002), Megonigal and Darke (2001), Perry and Atkinson (1997), The Nature Conservancy (1997).

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Click on the images below to open a larger image in a separate window.

	A mixed tidal oligohaline marsh with big cordgrass (Spartina cynosuroides), eastern rose-mallow (Hibiscus moscheutos ssp. moscheutos , with white flowers), and seashore mallow (Kosteletzkya virginica var. virginica , with pink flowers). Sweet Hall Marsh on the Pamunkey River, King William County.Photo: Phil Coulling / © DCR Natural Heritage.
	Tidal Oligohaline Marsh dominated by saltmeadow Cordgrass (Spartina patens) and Olney threesquare (Schoenoplectus americanus) at the mouth of Chotank Creek, King George County (Chotank Creek Natural Area Preserve).Photo: Gary P. Fleming / © DCR Natural Heritage.
	In Virginia, big cordgrass (Spartina cynosuroides) is the most characteristic and abundant species of tidal oligohaline marshes. Jamestown Island, James City County (Colonial National Historical Park).Photo: Gary P. Fleming / © DCR Natural Heritage.
	Bull-tongue arrowhead (Sagittaria lancifolia ssp. media) blooming among big cordgrass (Spartina cynosuroides) in a tidal oligohaline marsh on Jamestown Island, James City County (Colonial National Historical Park). Photo: Gary P. Fleming / © DCR Natural Heritage.
	Olney threesquare (Schoenoplectus americanus , with brown fruits) and dotted smartweed (Polygonum punctatum var. punctatum) in a tidal oligohaline marsh at the mouth of College Creek, James City County (Colonial National Historical Park). Photo: Gary P. Fleming / © DCR Natural Heritage.

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REPRESENTATIVE COMMUNITY TYPES:
Six community types have been classified based on analysis of data from 73 plots (map). Although most major oligohaline systems are represented, additional data are needed to refine the classification, especially of seemingly similar community types. Fundamental questions of how finely to split types and how much compositional variability to accept within type concepts still need to be addressed. The satisfactory classification, circumscription and assessment of communities dominated by narrow-leaved cattail remains particularly uncertain. Quantitative information on the riverine marshes of the bayside of the Eastern Shore (Pocomoke River watershed, Accomack County) are also sorely lacking. Click on any highlighted CEGL code below to view the global USNVC description provided by NatureServe Explorer.

• Spartina cynosuroides Tidal Herbaceous Vegetation
  Tidal Oligohaline Marsh (Big Cordgrass Type)
  USNVC: = CEGL004195
  Global/State Ranks: G4/S4
  
  
• Hibiscus moscheutos - Polygonum punctatum - Peltandra virginica - (Typha angustifolia, Spartina cynosuroides) Tidal Herbaceous Vegetation
  Tidal Oligohaline Marsh (Mixed Forbs Type)
  USNVC: = CEGL006181
  Global/State Ranks: GNR/S4
  
  
• Typha angustifolia - Hibiscus moscheutos Tidal Herbaceous Vegetation
  Tidal Oligohaline Marsh (Narrow-Leaved Cattail - Eastern Rose-Mallow Type)
  USNVC: = CEGL004201
  Global/State Ranks: G4G5/S3?
  
  
• Schoenoplectus americanus - Spartina patens Tidal Herbaceous Vegetation
  Tidal Oligohaline Marsh (Saltmeadow Cordgrass - Olney Three-Square Low Interior Marsh Type)
  USNVC: = CEGL006612
  Global/State Ranks: GNR/S3?
  
  
• Eleocharis rostellata - Spartina patens Tidal Herbaceous Vegetation
  Tidal Oligohaline Marsh (Beaked Spikerush - Saltmeadow Cordgrass Estuarine Fringe Type)
  USNVC: = CEGL006611
  Global/State Ranks: GNR/S1?
  
  
• Carex hyalinolepis Tidal Herbaceous Vegetation [Provisional]
  Tidal Oligohaline Marsh (Shoreline Sedge Type)
  USNVC: = CEGL006177
  Global/State Ranks: GNR/SU
  

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