Herbaceous riverbank/floodplain (S4)
Herbaceous riverbank/floodplains are wet to mesic meadows on silty or sandy soils along the banks of large rivers, small rivers, and large streams. They are dominated by various combinations of tall herbs, including reed canary grass, big bluestem, goldenrods, robust ferns, and various sedges. Shrubs and tree saplings mix with herbs in some examples, but amount to less than 25% cover. These medium to high riverbank communities sometimes extend onto adjacent floodplain settings, and can be similar in appearance to meadow marshes. In contrast to meadow marshes, however, there is little or no organic matter accumulation due to flood and ice scour, and rapid decomposition occurs during low water periods. This community is found statewide.
Characteristic Vegetation: Dominated by various combinations of tall herbs, including reed canary grass (Phalaris arundinacea), big bluestem (Andropogon gerardii), goldenrods (Solidago spp.), robust ferns, and various sedges.
Variants: The community is broadly defined, and five variants are described:
1.) Reed canary grass variant
This variant is dominated by reed canary grass (Phalaris arundinacea). Several other species occur with a cover of less than 1%. Soils are fine sand with some silt. This variant ranges from 1.0-1.8 m above midseason water levels. Its full distribution and abundance are not well documented.
Good examples of this variant occur along the Merrimack River, Cocheco River, and Little Cohas Brook.
2.) Bluejoint variant
The description for this variant is based on one site along the
This variant is dominated by a dense cover (60%) of bluejoint (Calamagrostis canadensis). Associates include tussock sedge (Carex stricta), lake sedge (C. lacustris), reed canary-grass (Phalaris arundinacea), meadowsweet (Spiraea alba), silky dogwood (Cornus amomum), northern arrowwood (Viburnum dentatum), nannyberry (Viburnum lentago), and scattered red maple (Acer rubrum), swamp white oak (Quercus bicolor), and American elm (Ulmus
A good example of this variant occurs along the Exeter River.
3.) Goldenrod variant
A dense cover of
Good examples of this variant occur along the Pemigewasset and Connecticut Rivers.
4.) Northern herbaceous variant
This variant occurs along several major streams and minor rivers north of the
Characteristic species include fringed brome grass (Bromus ciliatus), grass-leaved goldenrod (Euthamia graminifolia), broom sedge (Carex scoparia), Rudge’s sedge (C. debilis), tussock sedge (C. stricta), follicled sedge (C. folliculata), rough cinquefoil (Potentilla norvegica), Mexican muhly (Muhlenbergia mexicana), soft rush (Juncus effusus), neglected reed bent-grass (Calamagrostis stricta var. inexpansa), bent grasses (Calamagrostis spp.), currants (Ribes spp.), and moss species. Medium-height shrubs such as meadowsweet (Spiraea alba) and steeplebush (Spiraea tomentosa) are occasional or locally abundant.
A good example of this variant occurs along the Upper Ammonoosuc River.
5.) Inflated sedge variant
This variant is dominated by inflated sedge (Carex vesicaria) with lesser amounts of woolly bulrush (Scirpus cyperinus), rattlesnake mannagrass (Glyceria canadensis), reed canary grass (Phalaris arundinacea), tussock sedge (Carex stricta), and meadowsweet (Spiraea alba). Infrequent plants are bulbiferous water hemlock (Cicuta bulbifera), arrow-leaved tearthumb (Persicaria sagittata), false nettle (Boehmeria cylindrica), field bindweed (Convolvulus arvensis), and other species. This sedge-dominated meadow also supports a low shrub cover. The soil is silt and fine sand. Moderate-sized swales supporting this variant are sometimes intermixed in a mosaic dominated by silky dogwood.
A good example of the inflated sedge variant occurs along the Winnicut River.
6.) Big bluestem variant
Big bluestem (Andropogon gerardii) is diagnostic and is usually the most common herb. Woody plant richness is moderate, while cover is low to moderate. Scattered mature trees typically average around 5% cover.
Good examples of the big bluestem variant occur at Manchester River Outcrops (
Herbaceous riverbank/floodplains often occur as part of larger low-gradient silty-sandy riverbank systems, moderate-gradient sandy-cobbly riverbank systems, temperate minor river floodplain systems, montane/near boreal floodplain systems, and major river silver maple floodplain systems.
Herbaceous riverbank/floodplain along the Merrimack River in Canterbury (photo by Dan Sperduto)