Seasonally flooded Atlantic white cedar swamp (S2)
Seasonally flooded Atlantic white cedar swamps are uncommon in New Hampshire, occurring primarily along dammed streams in the Seacoast region and south-central parts of the state. It is found along open or moving water such as along lake, pond, and stream borders and in basins with impounded drainage. Unlike other Atlantic white cedar (Chamaecyparis thyoides) swamps, this community has a relatively open cedar canopy and numerous herbaceous species typical of marshy or open wetland habitats (species that are not found in the other Atlantic white cedar swamps). Species richness in this type is higher than other types of cedar swamps, although composition varies widely.
Some examples of this community naturally occur in seasonally flooded settings while others may be undergoing a shift in composition towards this type as a result of raised water levels from beavers or human impoundments. Atlantic white cedar in seasonally flooded settings may be more vulnerable to flood-extirpation than those with more isolated hydrologic conditions. Situations that are more susceptible to hydrologic or other alterations may not have a similar long-term viability.
Measurements of pH are generally among the highest recorded for cedar swamps in New Hampshire, falling between 4.4 to 6.5. Elevations range from 30 ft. to 250 ft. for coastal examples.
Characteristic Vegetation: Characteristic marsh plants include meadowsweet (Spiraea alba), bluejoint (Calamagrostis canadensis), tussock sedge (Carex stricta), northern blue flag (Iris versicolor), and marsh St. John’s-wort (Triadenum virginicum). Atlantic white cedar (Chamaecyparis thyoides) dominates the tree canopy. Other characteristic species include common arrowhead (Sagittaria latifolia), lesser bur-reed (Sparganium americanum), inflated sedge (Carex intumescens), common water horehound (Lycopus uniflorus), beggar ticks (Bidens spp.), bulbiferous water hemlock (Cicuta bulbifera), alder-buckthorn (Frangula alnus), highbush blueberry (Vaccinium corymbosum), winterberry (Ilex verticillata), cinnamon fern (Osmunda cinnamomea), sweet pepperbush (Clethra alnifolia), and peat moss (Sphagnum spp.). Other frequent species include follicled sedge (Carex folliculata), marsh fern (Thelypteris palustris var. pubescens), royal fern (Osmunda regalis var. spectabilis), and skunk cabbage (Symplocarpus foetidus).
The largely hummock-restricted upland species wild sarsaparilla (Aralia nudicaulis) and starflower (Trientalis borealis) are generally less constant than in the other types described, and boreal indicators are absent. Species much less frequent than in other Atlantic white cedar types include hemlock (Tsuga canadensis), mountain holly (Nemopanthus mucronatus), three-seeded sedge (Carex trisperma) and sheep laurel (Kalmia angustifolia).
Good examples of this community occur at Fairhill Swamp (Rye) and Locke Pond (Rye).
Seasonally flooded Atlantic white cedar swamps sometimes occur as part of coastal conifer peat swamp systems.
Seasonally flooded Atlantic white cedar swamp at Locke Pond in Rye (photo by Ben Kimball)
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