Subacid forest seep (S3S4)
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.
Subacid forest seeps exhibit weakly acidic conditions and are highly variable in species composition. Common plants of these seeps include foamflower (Tiarella cordifolia), rough sedge (Carex scabrata), small enchanter’s nightshade (Circaea alpina), and golden saxifrage (Chrysosplenium americanum). These communities occur throughout the state, with pH ranges from the mid 4s to 6.
Five fairly distinct variants are described based on differences in dominant life forms and species composition. The foamflower - graminoid and subacidic Sphagnum variants have a shallow muck layer (typically 10–30 cm) over sand or silt loams on slopes ranging from 1 to 24 degrees. Most examples of these two variants are headwater seeps associated with ephemeral or permanent streams. Measured pH’s are subacid and range from mid-5s to mid 6s. Nutrient levels are probably moderate to moderately high (mesotrophic) as indicated by the plant composition. The bryophyte - violet variant has subacid to somewhat circumneutral pHs and has shallow sandy muck over sand and gravel soils. They occur on till soils and along terrace slope faces. One example of the herbaceous - fern glade variant had 20–25 cm of muck over fine sand along a steep river terrace slope. The streamside variant typically has a shallow organic surface layer over mineral soil.
Variants: Five variants are currently described:
1. Foamflower - graminoid variant:
Typical of mid-elevation northern hardwood and semi-rich mesic forests, especially in the White Mountains region, and to a lesser extent other parts of the state. They are densely herb-dominated with a high graminoid (grass and sedge) component and low to moderate moss cover. Herbs diagnostic of this variant include foamflower, rough sedge, and/or northeastern mannagrass. Drooping woodreed may be present, though usually not dominant. Total graminoid cover often exceeds 35%, fern cover ranges from 5–20%, and total herbaceous cover exceeds 75% (>100% in some examples due to dense, overlapping herbs). Most examples are less than 0.1 acre and have 13–18 herb species present (some larger examples have more species). Good examples occur at Jeffers Brook and Black Mountain (Benton), Kelsey Mtn. (Millsfield), Spruce Brook (Berlin), Lincoln Brook (Lincoln), and along the Falling Waters Trail (Franconia).
2. Subacidic Sphagnum variant:
This variant differs from the foamflower - graminoid variant by the presence of a moderate to dense carpet of Sphagnum moss and a less dense herb layer. It differs from acidic Sphagnum seeps by the presence of species indicative of more minerotrophic conditions including foamflower, rough sedge, northeastern mannagrass, oak fern, two-leaved miterwort, and sensitive fern, among others. Frequent mosses include Sphagnum squarrosum, S. girgensohnii, and S. fallax. Good examples occur at Elbow Pond (Woodstock), Fairy Spring at Ice Gulch (Randolph), in the Trudeau Rd vicinity (Bethlehem), in the Moriah Brook headwaters (Bean's Purchase), and at Ammonoosuc Lake (Bethlehem).
3. Bryophyte - violet variant:
Bryophytes (mosses and liverworts) dominate with an apparent paucity of Sphagnum moss. The herb layer is variable; some seeps have a dense herb layer over the bryophyte layer while others are dominated solely by bryophytes. Violets may be abundant. These seeps may be associated with a strong coniferous overstory component (e.g., >50%). The primary diagnostic plants of the foamflower - graminoid variant are sparse or absent. Seepage plants may include violets (Viola spp.; including Viola cucullata), golden saxifrage, perfect-awned sedge, small enchanter’s nightshade, and dwarf raspberry, among others. Jack-in-the-pulpit and sensitive fern may also be present. Good examples occur at Allard Brook (Albany) and in the Shingle Pond vicinity (Chatham).
4. Herbaceous - fern glade variant:
A dense herb layer with a prominent fern and horsetail component is typical of this variant. The moss layer is variable. Herbs include sensitive fern, cinnamon fern, interrupted fern Osmunda claytoniana (interrupted fern), lady fern, wood horsetail, spotted touch-me-not, and awl sedge, among other seep plants. Graminoids are present but usually not a dominant life form as in the foamflower - graminoid variant. Good examples occur on a terrace slope above the Merrimack River (Sanbornton).
5. Streamside variant:
This variant occurs on low seepy benches or moderate to steep slopes immediately adjacent to upper perennial streams. Streambed gradients are moderate to high. Flood- and ice-scour and seasonal high water likely influence the vegetative structure and composition. Frequent herbs can include dwarf raspberry, foamflower, northern wood sorrel, northern wild licorice, water pennywort, golden saxifrage, small enchanter’s nightshade, tall meadow-rue (Thalictrum pubescens), white snakeroot, violets, northern lady fern, intermediate wood fern, ostrich fern (Matteuccia struthiopteris), interrupted fern, rough sedge, delicate sedge, northeastern mannagrass, and drooping woodreed. Shrubs include speckled alder and red elderberry (Sambucus racemosa), among others. Bryophyte cover is often high and includes Conocephalum conicum, Brachythecium rivulare, Plagiomnium ciliare, and Mnium sp. Good examples occur in the vicinities of Jobbers Brook (Pittsburg) and along the outlet stream of Boundary Pond (Pittsburg).
Subacid forest seeps often occur as inclusions within larger forest systems, and as part of forest seep/seepage forest systems.
subacid forest seep on the side of North Twin Mtn. (photo by Ben Kimball)
Subacid forest seep along stream at Black Mountain State Forest (photo by Pete Bowman)