Natural Communities of NH -- Photo Guide

Sugar maple - silver maple - white ash floodplain forest  (S1S2)

In sugar maple - silver maple - white ash floodplain forests, sugar maple and silver maple share dominance, and white ash is present. Floodplain ferns are common, as in the silver maple communities, but more upland forest herbs are present in this type. Rich woods indicator species such as Jack-in-the-pulpit and blue cohosh are sometimes present. Total species richness tends to be fairly high compared to other floodplain forest types, although herb cover is sparse. This community type is rare in New Hampshire. 

It occurs primarily along northern rivers with a lot of channel sediments and is floristically intermediate between silver maple dominated floodplain forests and the sugar maple - ironwood - short husk floodplain forest. It generally has the same structural features as those other communities, with over-arching hardwoods and a fern and forb understory with few shrubs, but lower canopy density and higher fern cover than the other sugar maple type. Total and relative species richness values are similar to the other sugar maple type. It is found either along the river’s edge or on high terraces far from the river, but is flooded during spring runoff. Found along mostly central and northern rivers with high energy and chaotic flood regimes. The back-terrace type is found as far south as Concord, along the Merrimack River, but it is primarily found in the Saco and Androscoggin River drainages. 

Northern examples occur on higher terraces and are similar to the sugar maple - ironwood - short husk floodplain forest, with evidence of high intensity flood pulses. Southern examples tend to occur in back-channel landscape positions. The back-channel examples have little microtopographic variation, instead forming broad flat terraces that may be lower in elevation than the surrounding landscape, with features suggesting an abandoned river channel.

Soils are variable, but tend to be well to moderately well drained sandy loams in northern examples, and somewhat poorly drained silty loams in southern examples. Soils are slightly enriched in most examples, supporting several rich-site herbs, but they are not as enriched as the silver maple - wood nettle - ostrich fern floodplain forest

Characteristic vegetation: Silver maple (Acer saccharinum) and sugar maple (Acer saccharum) share canopy dominance with white ash (Fraxinus americana). The presence of ash is diagnostic and may be related to the somewhat enriched soils of this type. black cherry (Prunus serotina) is present in some higher terrace examples, and American elm (Ulmus americana) occasionally grows in the sub-canopy, along with occasional northern hardwood species, including yellow birch (Betula alleghaniensis). poison ivy (Toxicodendron radicans) is a common vine, while northern short husk grass (Brachyelytrum erectum) and inflated sedge (Carex intumescens) are common graminoids. 

Sensitive fern (Onoclea sensibilis) and ostrich fern (Matteuccia struthiopteris var. pensylvanica), diagnostic ferns of the two silver maple floodplain forest types, occur together with herbs more commonly found in upland northern forests. These herbs include sessile-leaved bellwort (Uvularia sessilifolia), Canada mayflower (Maianthemum canadense), false Solomon's seal (Maianthemum racemosum), andwhite wood aster (Aster divaricatus). Rich woods indicator herbs such as Jack-in-the-pulpit (Arisaema triphyllum) and blue cohosh (Caulophyllum thalictroides) are occasional, most often occurring in examples dominated by sugar maple (as opposed to silver maple).

Good examples
of this community occur along the Saco River (Bartlett to Conway) and the Pemigewasset River (Woodstock to New Hampton).

Sugar maple - silver maple - white ash floodplain forests often occur as part of a montane/near-boreal floodplain system, and sometimes as part of major river silver maple floodplain systems.

Dried channel through SM - SM - WA FPF along the Merrimack River (photo by Ben Kimball for the NH Natural Heritage Bureau)
Sugar maple - silver maple - white ash floodplain forest
along the Merrimack River (photo by Ben Kimball)

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