Balsam fir floodplain/silt plain (S2)
Balsam fir floodplain/silt plains occur in northern and sometimes central
Floodplain soils are fine sandy loams or loams that occur in valley bottoms of montane rivers or other settings with frigid soils or pronounced cold-air drainage (NRCS frigid temperature regime). Flashy montane rivers are associated with several examples of this floodplain type and may be indicative of a more temporary or infrequently flooded regime compared to other floodplain forest community types. Known examples occur from 150 m (500 ft.) to more than 370 m (1200 ft.) elevation. Silt plain soils are somewhat poorly drained silt loams.
Characteristic vegetation: Balsam fir is usually abundant or co-dominant in the canopy or subcanopy along with red maple. White pine and black cherry (Prunus serotina) are frequent and occasionally abundant, and silver maple is occasional. Hemlock (Tsuga canadensis) and red spruce (Picea rubens) are infrequent. Species found in other floodplain forest types but more frequent or abundant in this type include bluejoint (Calamagrostis canadensis), small tussock sedge (Carex stricta), meadowsweet (Spiraea alba var. latifolia), northern short husk grass (Brachyelytrum septentrionale), New England sedge (Carex novae-angliae), beaked hazelnut (Corylus cornuta), and inflated sedge (Carex intumescens). Northern or boreal plants are frequent as a group and include goldthread (Coptis trifolia), bunchberry (Cornus canadensis), and whorled aster (Oclemena acuminata). Tussock sedge is nearly constant but usually present only in its rhizomatous form (e.g., non tussock-forming).
Common floodplain forest species found in this community include sensitive fern (Onoclea sensibilis), tall meadow-rue (Thalictrum pubescens), witherod (Viburnum nudum var. cassinoides), northern arrowwood (Viburnum dentatum var. lucidum), rough goldenrod (Solidago rugosa), royal fern (Osmunda regalis var. spectabilis), speckled alder (Alnus incana ssp. rugosa), and sessile-leaved bellwort (Uvularia sessilifolia).
Variants: Two variants are described:
1. Floodplain variant:
As described above.
2. Silt plain variant:
This variant differs from the floodplain variant by having siltier soils, a moderate cover of speckled alder, and other plants indicative of higher nutrient and moisture availability (presumably a result of the higher silt content of soils). Most examples have a woodland structure. Many of the species found in the floodplain variant can also occur in this variant. At some sites this variant transitions into alder alluvial shrubland. Species most characteristic of the silt plain variant include red elderberry (Sambucus racemosa), dwarf raspberry (Rubus pubescens), foamflower (Tiarella cordifolia), inflated sedge (Carex intumescens), tall meadow-rue (Thalictrum pubescens), purple avens (Geum rivale), crested wood fern (Dryopteris cristata), white turtlehead (Chelone glabra), Jack-in-the-pulpit (Arisaema triphyllum), northern lady fern (Athyrium filix-femina var. angustum), ostrich fern (Matteuccia struthiopteris var. pensylvanica), false hellebore (Veratrum viride), highbush cranberry (Viburnum opulus), and hooked buttercup (Ranunculus recurvatus).
Good examples of this community occur along Indian Stream (Pittsburg), Androscoggin River (Errol), Swift River (Albany), Pine River (Ossipee), and Big River (Barnstead).
Balsam fir floodplain/silt plains often occur as part of larger montane/near-boreal floodplain systems and temperate minor river floodplain systems.
Balsam fir floodplain/silt plain along the Swift River (photo by Ben Kimball)
Balsam fir floodplain/silt plain along the Swift River (photo by Ben Kimball)