Circumneutral hardwood forest seep
Circumneutral hardwood forest seep (S3)
Forest seeps are very small wetlands, typically less than one acre in size, that occur around groundwater discharge areas in upland forests. Species composition varies among sites, but collectively seeps are diverse and support a unique flora and fauna. Despite their small size, seeps add a distinct biological component to the matrix of upland forests. Many herbs, sedges, and mosses are restricted to forest seeps or other seepage wetlands.
Circumneutral hardwood forest seeps have neutral or weakly acidic soil water (pH generally higher than 6), and are less common than subacid seeps. They feature a higher amount of nutrient availability compared to subacid or acidic seeps (below ca. 6.4 and 5.3, respectively). They occur as small ovoid seeps, as linear “seepage runs” within a forest, or zones along river terrace slopes. They are characterized by a mixture of seepage indicators and other wetland plants along with rich mesic hardwood plants such as wood nettle, ostrich fern, zigzag goldenrod, and plantain-leaved sedge. They occasionally support populations of rare plants such as Goldie’s fern, yellow lady’s slipper, and Loesel’s twayblade. These seeps are treated here as one broadly defined group with three variants. Larger examples are classified as seepage swamps or seepage forests.
Soils are either shallow mucks or silty, gravelly mucks (10–25 cm) over silt loams, silt, or clay soils. Soils are derived from intermediate bedrock and till or marine silt and clay sediments. In most examples, pHs range from 6.5–7.4.
Characteristic vegetation: Diagnostic rich-site plants that differentiate this community include the trees sugar maple (Acer saccharum), white ash (Fraxinus americana), black ash (Fraxinus nigra), and basswood (Tilia americana), and herbs and shrubs including wood nettle (Laportea canadensis), ostrich fern (Matteuccia struthiopteris), zigzag goldenrod (Solidago flexicaulis), plantain-leaved sedge (Carex plantaginea), blue cohosh (Caulophyllum thalictroides), narrow-leaved spleenwort (Diplazium pycnocarpon), Christmas fern (Polystichum acrostichoides), Goldie’s fern (Dryopteris goldiana), white baneberry (Actaea pachypoda), large yellow lady’s-slipper (Cypripedium pubescens), rattlesnake-fern (Botrychium virginianum), northern maidenhair fern (Adiantum pedatum), purple-flowering raspberry (Rubus odoratus), and downy yellow violet (Viola pubescens).
Other documented species include violets (Viola spp.), lady fern (Athyrium filix-femina), oak fern (Gymnocarpium dryopteris), tall meadow-rue (Thalictrum pubescens), marsh fern (Thelypteris palustris), small mannagrass (Glyceria striata), and bedstraws (Galium spp.). Dwarf scouring-rush (Equisetum scirpoides) is an uncommon plant that may be expected in northern seeps in coniferous or some deciduous forests.
Variants: Three variants are described:
1. Northern hardwood variant (typic):
Characterized by seepy fern and nettle glades, always with a high cover of ferns, particularly northern lady fern (Athyrium filix-femina var. angustum), ostrich fern (Matteuccia struthiopteris var. pensylvanica), and/or wood nettle (Laportea canadensis). Diagnostic rich-site plants include zigzag goldenrod (Solidago flexicaulis), plantain-leaved sedge (Carex plantaginea), blue cohosh (Caulophyllum thalictroides), narrow-leaved spleenwort (Diplazium pycnocarpon), Christmas fern (Polystichum acrostichoides), Goldie's fern (Dryopteris goldiana), white baneberry (Actaea pachypoda), large yellow lady's slipper (Cypripedium parviflorum var. pubescens), rattlesnakefern (Botrychium virginianum), northern maidenhair fern (Adiantum pedatum), purple-flowering raspberry (Rubus odoratus), and downy yellow violet (Viola pubescens). Trees that may be expected include sugar maple (Acer saccharum), white ash (Fraxinus americana), black ash (Fraxinus nigra), and basswood (Tilia americana).
2. Coastal/ Appalachian variant:
Occurs in coastal and southern New Hampshire, with many of the rich-site species of the typic variant. Additional species may include small-crested sedge (Carex cristatella), drooping sedge (Carex crinita), northern spicebush (Lindera benzoin), stellate sedge (Carex radiata), star sedge (Carex rosea), hog-peanut (Amphicarpaea bracteata), black maple (Acer nigrum), musclewood (Carpinus caroliniana), and black birch (Betula lenta). Appalachian oaks and hickories are often prominent in the surrounding forest. Boreal conifers are absent, while red maple may be frequent. Some examples are almost fen-like, with a strong graminoid component.
3. River terrace slope variant:
Occur along enriched river terrace slope. Often contain smooth scouring-rush (Equisetum hyemale ssp. affine) and ostrich fern (Matteuccia struthiopteris var. pensylvanica), along with other seep or wetland plants such as rough sedge (Carex scabrata), spotted touch-me-not (Impatiens capensis), white turtlehead (Chelone glabra), and speckled alder (Alnus incana ssp. rugosa).
Circumneutral hardwood forest seeps often occur as inclusions within larger forest systems, and as part of forest seep/seepage forest systems.
Forest seep at Saint-Gaudens National Historic Site (photo by Ben Kimball)