Mesic herbaceous river channel (S4)
[Note: this community is a combination of two former types: herbaceous low riverbank and herbaceous sandy river channel]
Mesic herbaceous river channel communities occur on coarse substrate of low riverbanks, channel shelves, and bars subjected to flood and ice scour in moderate- to high-energy settings along rivers and large streams. Moisture conditions are mesic to hydric through most or all of the growing season. Sandy to sand-cobble soils are flooded early in the growing season and range from being wet through much or all of the growing season in lower areas to more mesic on slightly higher ground.
Herbs dominate, and shrubs are absent or sparse. Short to moderate-height herbaceous wetland forbs, grasses, sedges, and ferns comprise a sparse to dense cover. Cardinal flower (Lobelia cardinalis), water purslane (Ludwigia palustris), and beggar’s ticks (Bidens spp.) are common. Plants that can survive in emerged or submerged condition, such as smartweeds (Polygonum spp.) and swamp candles (Lysimachia terrestris), are also present. This community is one of the lowest in the channel supporting emergent species and may be adjacent to aquatic beds in deeper water. As with other communities associated with the river channel, this community migrates with channel shifts.
In some examples of this community, higher portions dry out in late summer, and support many of the same short, stress-tolerant graminoids found in sandy pond shore marshes, such as cut-grasses (Leersia spp.), rushes (Juncus spp.), and sedges such as bulrushes (Scirpus spp.) and spike-rushes (Eleocharis spp.).
Characteristic vegetation: This is a broadly defined community characterized by short to medium height, facultative wetland herbs and disturbance colonizers. Shrub and tree seedlings are absent to sparse. Species richness, composition, and cover from one example to the next can be quite variable and likely relates to the variable environmental conditions, propagule availability, and disturbance dynamics of stream channels. Graminoids that may be present include Poa spp. (blue-grasses), Panicum spp. (panic grasses), Glyceria spp. (manna-grasses), Leersia spp. (cut-grasses), Calamagrostis canadensis (blue-joint), Echinochloa spp. (barnyard-grasses), Eragrostis spp. (love-grasses), Agrostis spp. (bent grasses), Phalaris arundinacea (reed canary-grass), Juncus spp. (rushes), Eleocharis spp. (spike-rushes), Carex spp. (sedges), Cyperus spp. (umbrella-sedges), and Scirpus spp. (bulrushes).
Forbs may include Galium spp. (bedstraws), Cicuta spp. (water-hemlocks), Impatiens capensis (spotted touch-me-not), several fern species, Viola spp. (violets), Polygonum spp. (smartweeds), Hypericum spp. (St. John's-worts), Bidens spp. (sticktights), Lycopus uniflorus (common water horehound), Iris versicolor (northern blue flag), Apocynum sibiricum (prairie dogbane), Eupatorium spp. (Joe-pye-weeds), Lysimachia terrestris (swamp candles), Lobelia cardinalis (cardinal-flower), Ludwigia palustris (water purslane), Boehmeria cylindrica (false nettle), Pilea pumila (clearweed), Sium suave (water parsnip), Cicuta spp. (water-hemlocks), and several others.
This community occurs statewide. Good examples occur along Berry's Brook (Rye), Lamprey River (Epping), Blackwater River (Salisbury), Livermore Falls (Holderness), Swift River (Albany), Saco River (Conway), and by outcrops along the Merrimack River (Manchester).
Mesic herbaceous river channel communities often occur as part of larger low-gradient silty-sandy riverbank systems or moderate-gradient sandy-cobbly riverbank systems.
Mesic herbaceous river channel along the Blackwater River in Salisbury
(photo by Dan Sperduto)
Mesic herbaceous river channel along the Swift River (photo by Dan Sperduto)
Mesic herbaceous river channel along the Blackwater
River in Salisbury (photo by Dan Sperduto)