Natural Communities of NH -- Photo Guide

Silver maple - wood nettle - ostrich fern floodplain forest  (S2)



The silver maple - wood nettle - ostrich fern floodplain forest is one of two distinct silver maple dominated floodplain forest community types in New Hampshire. It occurs mostly on the Connecticut River, and less commonly elsewhere. Silver maple dominates the tree canopy and forms a tall, arching, cathedral-like ceiling above the level floodplain adjacent to the river channel. Ostrich fern and northern lady fern dominate the understory, often with an abundance of wood nettle. The graminoid and shrub cover is notably sparse. 

These riparian forests are found along large rivers, often associated with a confluence between the mainstem and a tributary, though they also develop along river meanders or other slow moving areas of the river course. They are flooded annually with peak floods in spring from snowmelt and drainage higher in the watershed. Additionally, flood regimes are now artificially controlled along rivers with this community type. This community occupies lower floodplains with deep, alluvial, silty soils. 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. Sloughs and drainage channels can be up to two meters deep and often support marsh vegetation soon after floodwaters recede.

The tree layer is uniformly dominated by silver maple (Acer saccharinum), with white ash (Fraxinus americana), American elm (Ulmus americana), and eastern cottonwood (Populus deltoides) present in varying proportions. hackberry (Celtis occidentalis) and butternut (Juglans cinerea) can occur in Connecticut River examples, especially along the river or upland edge. Similar tree species are usually growing in the sub-canopy, however shrubs and vines grow only along edges or in recent gaps created by natural or human-induced disturbance. Otherwise, the shrub layer is typically poorly developed or absent. A rich, thick carpet of herbaceous growth under the over-arching canopy creates an open, high-ceiling, cathedral-like appearance in most examples.

The herb layer is often strongly dominated by lush ostrich fern (Matteuccia struthiopteris var. pensylvanica) and wood nettle (Laportea canadensis), both of which can grow 1.8 m (6 ft.) tall. Other herbaceous and vine species are usually present, but never dominant, include sensitive fern (Onoclea sensibilis), northern lady fern (Athyrium filix-femina var. angustum), common woodreed (Cinna arundinacea), false nettle (Boehmeria cylindrica), spotted touch-me-not (Impatiens capensis), tall meadow-rue (Thalictrum pubescens), Jack-in-the-pulpit (Arisaema triphyllum), Virginia creeper (Parthenocissus quinquefolia), and spotted Joe-pye-weed (Eupatorium maculatum). The rare green dragon (Arisaema dracontium) is found in some examples along the Connecticut River, in low floodplain terraces among the ostrich fern.

On average, forb cover in this community is nearly twice that of other floodplain forest natural communities. Total herb cover is also higher, and fern cover is the highest of any floodplain forest type in the state. Conversely, the cover of graminoid, shrub, and sub-canopy trees is low, especially compared to red maple floodplain forests.

Soils are generally somewhat poorly drained to moderately well drained silt loams or very fine sandy loams. Due to the dynamic nature of flooding and an almost yearly deposition of new soil material, the development of soil horizons is virtually absent. Organic debris from leaf litter and flood wash is occasionally buried under new silt and sand deposits creating layers or lenses of slowly decomposing organic matter, interspersed with either orange-red mottled sediments, or pure gray silt. Soil pH is highly variable. Average pH is 5.7, but more basic examples are found along the Connecticut River, perhaps due to the more base-rich bedrock in this part of the state. Watershed size varies widely, but most examples are found where upstream basin size exceeds 2,000 square miles.


Good examples of this community occur along the Connecticut River (Northumberland, Haverhill, and Walpole).

Silver maple - wood nettle - ostrich fern floodplain forests often occur as part of major river silver maple floodplain forest systems.


Floodplain forest at Bedell Bridge State Park (photo by Ben Kimball for the NH Natural Heritage Bureau)
Floodplain forest at Bedell Bridge State Park (photo by Ben Kimball)

Floodplain forest at Bedell Bridge State Park (photo by Ben Kimball for the NH Natural Heritage Bureau)
Floodplain forest at Bedell Bridge State Park (photo by Ben Kimball)

Silver maple and wood nettle in floodplain forest at Bedell Bridge State Park (photo by Ben Kimball for the NH Natural Heritage Bureau) 1.  Ostrich fern in floodplain forest at Bedell Bridge State Park (photo by Ben Kimball for the NH Natural Heritage Bureau) 2.
1. Silver maple and wood nettle in floodplain forest at Bedell Bridge State Park (photo by Ben Kimball)
2. Ostrich fern in floodplain forest at Bedell Bridge State Park (photo by Ben Kimball)


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