Natural Communities of NH -- Photo Guide

Three-way sedge - mannagrass mudflat marsh  (S2S3)



Three-way sedge - mannagrass mudflat marsh
is a densely vegetated, semi-permanently flooded “mudflat” community dominated by short forbs and graminoids (<0.65 m). In New Hampshire, it is restricted to mucky, closed sand plain basins in central and southern parts of the state. This is a semi-permanently flooded community found in mucky sand plain basins. Periodic water level drawdowns produce mudflat conditions with dense vegetation. Prominent life forms include spongy-tissued, floating-stemmed, and other rhizomatous species, short clumped graminoids, and annual plants. Dominant plants in this community are broadly distributed species tolerant of fluctuating water levels. Few if any coastal plain species are present. 

This community is wetter than and has a lower abundance of tall graminoids compared to meadowsweet - robust graminoid sand plain marshes and twig rush sandy turf pond shores, and a lower abundance of ruderals and floating-leaved aquatics than spike-rush - floating-leaved aquatic mudflat marsh. A higher proportion of the species in this community have a more general or northern distribution than the coastal plain species found in meadow beauty sand plain marsh, twig rush sandy turf pond shore, and bulblet umbrella-sedge open sandy pond shore communities. The community is commonly found just above the wetter spike-rush - floating-leaved aquatic mudflat marsh community.

Soils have 20–110 cm (average=57 cm) of O horizon with a muck A horizon over sand, gravel, or slightly silty-gravelly sand. Moderate to deep muck soils are typical, forming mudflat conditions during draw-down periods.

Characteristic vegetation: Frequent characteristic species include the aerenchymatous (spongy-tissued) Dulichium arundinaceum (three-way sedge)(usually a dominant);floating-stemmed species Glyceria borealis (northern floating mannagrass) and Puccinellia pallida (pale mannagrass); short rhizomatous graminoids including Eleocharis smallii (Small’s spike-rush), E. flavescens (olive-brown spike-rush), and Juncus pelocarpus (mud rush); and rhizomatous forbs including Hypericum boreale (northern St. John’s-wort), Triadenum virginicum (marsh St. John’s-wort), Viola lanceolata (lance-leaved violet), and Lysimachia terrestris (swamp candles). Tall graminoids are occasional and in moderately low abundance, including Carex vesicaria (inflated sedge) and C. utriculata (bottle-shaped sedge). Sphagnum moss is occasional and in low abundance. Mudflat annuals are frequent as a group and occasionally abundant, but inconsistent as to species. These include Eleocharis obtusa (blunt spike-rush), Lindernia dubia (common false pimpernel), Scirpus smithii (Smith’s bulrush), Bidens connata (swamp beggar-ticks), B. frondosa (common beggar-ticks), and Erechtites hieracifolia (fireweed).


Good examples of this community occur in the lower Merrimack River Valley region.

Three-way sedge - mannagrass mudflat marsh often occurs as part of a sand plain basin marsh system.

(no photo available)

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