Alder seepage thicket (S3)
Alder seepage thicket is a tall shrub swamp community that occurs in nutrient-enriched settings within depressions and on slopes fed by groundwater seepage. Alders dominate over a diverse and moderately well developed herbaceous layer of species indicative of mineral enrichment or groundwater seepage. Mineral soils with a shallow muck layer are typical in this community, and they are saturated or seasonally saturated. This community can be found throughout
Characteristic Vegetation: Speckled alder (Alnus incana ssp. rugosa) is the dominant tall shrub, forming a canopy that can vary from dense to moderately open. The herb layer is diverse, and can include marsh marigold (Caltha palustris), golden saxifrage (Chrysosplenium americanum), spotted touch-me-not (Impatiens capensis), sensitive fern (Onoclea sensibilis), foamflower (Tiarella cordifolia), perfect-awned sedge (Carex gynandra), mannagrasses (Glyceria spp.), and bluejoint (Calamagrostis canadensis), as well as numerous other herbs and mosses generally absent in peatlands.
Good examples of this community occur at South Bay Bog (
Alder seepage thickets often occur as part of larger emergent marsh - shrub swamp systems, and sometimes as part of near-boreal minerotrophic peat swamp systems, temperate minerotrophic swamp systems, and forest seep/seepage forest systems.
Alder seepage thicket at Coleman State Park (photo by Pete Bowman)
Alder seepage thicket, transitional to red maple - black ash swamp
marsh marigold in bloom in the understory (photo by Dan Sperduto)
Alder seepage thicket at Great Bay NWR in Newington (photo by Ben Kimball)