Natural Communities of NH -- Photo Guide

Silver maple - false nettle - sensitive fern floodplain forest  (S2)



In New Hampshire, silver maple - false nettle - sensitive fern floodplain forest is found primarily in central and southern parts of the state on various large and medium-sized rivers. The canopy is dominated by silver maple, which forms a tall, arching, cathedral-like ceiling above the level floodplain adjacent to the river channel. American elm often occurs in association. The understory is distinguished by a diverse and variable ground cover, abundant sensitive fern, and the presence of false nettle and common woodreed. There is a high degree of microtopographic variation, with sand levees near the river’s edge, riparian vernal pools, soil depressions surrounding large tree trunks, and sloughs. It is most common on the Merrimack River and along medium-sized rivers such as the Ashuelot and the Contoocook. It also sometimes occurs as a very narrow border along riverbanks, transitional to other floodplain forest types (e.g. red maple floodplain forest).

It is the most common silver maple floodplain forest community type in the state, except along the Connecticut River where silver maple - wood nettle - ostrich fern floodplain forest is more common. It is similar to that other community, but distinguished by a variety of factors. For example, it has a more diverse ground cover. It also tends to occur on sandier and generally more acidic soil, on more medium-sized rivers. While flooding intensity and frequency are comparable in both of the silver maple types, this one may be characterized by floods of shorter duration and higher disturbance. A lack of species such as white ash (Fraxinus americana), hackberry (Celtis occidentalis), and butternut (Juglans cinerea) hint at the more acidic nature of the soils in this type. Herb species diversity and richness is higher and more variable in this type as well. This type has a distinctly higher graminoid % cover, higher total herb species richness, and lower tree species richness. Total forb species richness is also higher, but fewer species are encountered from site to site. Graminoid species presence, richness, and diversity are all higher in this type. 

Soils are highly variable, ranging from somewhat poorly drained silt loams to well drained sandy loams. Soil pHs tend to be slightly acidic (average pH=5.3), perhaps related to base-poor bedrock in these east-central drainage basins. This type is generally found on rivers with drainage basins less than 1,000 square miles in area above site locations, although some Merrimack River examples have upstream basin areas approaching 2,000 square miles.

Characteristic vegetation: 
Silver maple (Acer saccharinum) dominates the tree canopy, with American elm (Ulmus americana) as a subcanopy associate. Shrubs are not prevalent in this type, except on edges and canopy gaps; patches of meadowsweet(Spiraea alba) can occur in drier microhabitats and buttonbush (Cephalanthus occidentalis) grows in wet sloughs or channels. The herb layer is usually dominated by sensitive fern (Onoclea sensibilis) or co-dominated by sensitive fern andfalse nettle (Boehmeria cylindrica). Ostrich fern (Matteuccia struthiopteris var. pensylvanica) may be present in some examples but there is a notable lack of wood nettle (Laportea canadensis). Poison ivy (Toxicodendron radicans) is prevalent (as opposed to only occasional in the other silver maple type). Other forbs are similar to the other type, but graminoid species such as common woodreed (Cinna arundinacea), drooping woodreed (Cinna latifolia), drooping sedge (Carex crinita), Virginia cutgrass (Leersia virginica), and inflated sedge (Carex intumescens) are present as well. River grape and other vine species may be abundant along the community's edges and in canopy gaps.



Good examples of this community occur along the Merrimack River (Franklin to Concord), Contoocook River (Hillsboro to Concord), Ashuelot River (Keene to Winchester), and Blackwater River (Salisbury).

Silver maple - false nettle - sensitive fern floodplain forests often occur as part of major river silver maple floodplain forest systems, and less occasionally as part of temperate minor river floodplain systems.  


Silver maple - false nettle - sensitive fern floodplain forest along the Merrimack River in Concord (photo by Ben Kimball for the NH Natural Heritage Bureau)
Silver maple - false nettle - sensitive fern floodplain forest
along the Merrimack River in Concord (photo by Ben Kimball)

Silver maple floodplain forest along the Merrimack River in Concord (photo by Ben Kimball for the NH Natural Heritage Bureau)
Silver maple floodplain forest along the Merrimack River in Concord (photo by Ben Kimball)

Silver maple floodplain forest near the NH Technical Institute along the Merrimack River in Concord (photo by Ben Kimball for the NH Natural Heritage Bureau)
Silver maple floodplain forest near the New Hampshire Technical Institute
along the Merrimack River in Concord (photo by Ben Kimball)

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