Natural Communities of NH -- Photo Guide

Sugar maple - ironwood - short husk floodplain forest (S1)

Sugar maple - ironwood - short husk floodplain forests
occur within the low floodplain terraces of high-gradient rivers in northern parts of the state. They have a dense tree canopy (relatively high percent cover of canopy trees compared to silver maple types) and the sparsest fern and herb layer of any floodplain forest community. Silver maples are absent, though they may occur along the riverbank or on lower terraces. Plant associations are similar to upland forests, but show considerable evidence of periodic, high intensity flood events that may only temporarily disrupt plant growth. The variability of flooding intensity and frequency creates a diverse suite of microhabitats within sites.

Though rare in the state, this is the primary floodplain forest along upstream reaches of central and northern rivers that drain mountainous terrain and have flashy flood regimes, like the upper Saco and Pemigewasset Rivers. Flood regulation is less common on these rivers. The steeper-gradient river channels and strong pulse flood regime characteristic of these rivers leads to high energy, short duration flooding events. Evidence of energetic flood pulses includes steep riverbanks, coarse sand deposition, cobble-lined slough channels, patches of cobbles supporting early successional woody vegetation along river edges, and occasional piles of dead woody debris. Total species richness tends to be fairly high compared to other floodplain forest types, although herb cover is sparse. Overall, the species composition indicates somewhat drier conditions than other floodplains. This type has the lowest fern cover of any floodplain forest natural community; cover of upland forbs and grasses is similar to other floodplain forests. 

Soils are somewhat poorly to well drained and generally alluvial, often with buried organic layers beneath fresh sandy alluvium. The upper 15–50 cm of sandy soil is usually finer textured than underlying soil; pHs consistently range from 5.0–5.4 in the top 50 cm. This community frequently occurs in areas mapped as Suncook, Ondawa, or Colton soil series.

Characteristic vegetation:
The vegetation structure and composition is quite consistent for these maturing (65–100 year-old), second-growth forests. The 20–25 m tall, closed tree canopy is dominated by sugar maple (Acer saccharum), red oak (Quercus rubra), with black ash (Fraxinus nigra) and white pine (Pinus strobus) of secondary importance. Other occasional tree species include basswood (Tilia americana), silver maple (Acer saccharinum), and red maple (Acer rubrum). The subcanopy consistently has sugar maple and ironwood (Ostrya virginiana). Shrubs are generally sparse, except at the edges. Herbs are lush, with the most abundant and common being blue-stemmed goldenrod (Solidago caesia), sessile-leaved bellwort (Uvularia sessilifolia), poison ivy (Toxicodendron radicans), wild sarsaparilla (Aralia nudicaulis), long-stalked sedge (Carex pedunculata), and northern short husk grass (Brachyelytrum septentrionale). The abundance of blue-stemmed goldenrod and short husk grass is the most floristically distinct aspect of this forest type. A naturalized grass, wood bluegrass (Poa nemoralis), is also present. 

Compared to average northern hardwood forests, the herb layer is often more lush – commonly with a high total percent cover value. The most abundant or common species are Solidago caesia (blue-stemmed goldenrod), Uvularia sessilifolia (sessile-leaved bellwort), Toxicodendron radicans (poison ivy), Aralia nudicaulis (wild sarsaparilla), Carex pedunculata (long-stalked sedge), and Brachyelytrum erectum (northern short husk grass). The abundance of blue-stemmed goldenrod and northern short husk grass is the most floristically distinct aspect in this community. A naturalized grass, Poa nemoralis (wood bluegrass), is also frequent. Overall, the composition of this type indicates somewhat drier conditions compared to soil moisture levels in other floodplain forest communities.

Formal variants are not described, but northern floodplain terraces often support softwoods among the hardwoods. At other sites, there may be decreased importance of sugar maple and the increased importance of red oak, hemlock (Tsuga canadensis), and American beech (Fagus grandifolia). These also have a notable lack of herb cover, with species composition tending towards that found in acid woods. Furthermore, the soils at these mixed woods sites tend to be coarser (loamy sands over sands and gravel) and drier.

Good examples of this community occur along the Saco River (Bartlett to Conway).

Sugar maple - ironwood - short husk floodplain forests often occur as part of larger montane/near boreal floodplain systems.

sugar maple - ironwood - short husk floodplain forest (photo by Dan Sperduto for the NH Natural Heritage Bureau)
sugar maple - ironwood - short husk floodplain forest (photo by Dan Sperduto)

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