Natural Communities of NH -- Photo Guide

Red maple - sensitive fern swamp  (S3S4)

Red maple - sensitive fern swamps
are a common type of (weakly) minerotrophic red maple swamp in central and southern New Hampshire characterized by a diverse assemblage of herbaceous species, relatively little Sphagnum moss, and saturated or seasonally saturated to seasonally flooded soils. The swamps range from small or very large (10-100 acres) and typically occupy headwater basins that give rise to drainages or occur along drainages where seepage or non-channelized upland runoff contributes to the water budget. They occur on seasonally saturated or seasonally flooded mineral or muck soils. 

The community lacks seasonal flooding from over-bank flooding (as is typical of seasonally flooded red maple swamps) and is more minerotrophic than red maple - Sphagnum basin swamps. Onoclea sensibilis (sensitive fern) is a good indicator of minerotrophic conditions in this type. Subsurface groundwater discharge is likely in at least some of these swamps. In contrast to red maple - black ash swamps and red maple - lake sedge swamps, surface or near-surface runoff is the predominant source of external nutrients. These swamps are often found in a mosaic with other swamp communities in a larger temperate minerotrophic swamp systems 

Characteristic vegetation: Tree cover ranges from 25% to more than 65% and consists of red maple (Acer rubrum), with lesser quantities of American elm (Ulmus americana) and other hardwoods, and few or no conifers. A diverse shrub layer is typical; winterberry (Ilex verticillata) is abundant and highbush blueberry (Vaccinium corymbosum) is usually present but less abundant than in nutrient-poor swamps. Northern arrowwood (Viburnum dentatum), speckled alder (Alnus incana ssp. rugosa), and meadowsweet (Spiraea alba) are occasional. Poison sumac (Toxicodendron vernix), poison ivy (Toxicodendron radicans), common elderberry (Sambucus canadensis), northern spicebush (Lindera benzoin), nannyberry (Viburnum lentago), and silky dogwood (Cornus amomum) may be present.

Tussock sedge (Carex stricta) and sensitive fern (Onoclea sensibilis) are usually abundant or co-dominant herbs. Other species include spotted touch-me-not (Impatiens capensis), northern blue flag (Iris versicolor), swamp candles (Lysimachia terrestris), drooping sedge (Carex crinita), royal fern (Osmunda regalis), bluejoint (Calamagrostis canadensis), and violets (Viola spp.). Cinnamon fern (Osmunda cinnamomea) is often present but not dominant throughout. Brome sedge (Carex bromoides) is abundant in some examples.

Mosses are often abundant and diverse, but peat moss (Sphagnum spp.) typically comprises less than 5% cover, or is absent. Hummock-hollow topography ranges from absent to moderately well developed.

Upland species found on large hummocks of more acidic basin swamps appear to be less abundant in these swamps (such as wild sarsaparilla, partridgeberry, and red oak). Also, while this community is somewhat minerotrophic, plant species indicative of mineral-rich groundwater seepage are absent or sparse.

Good examples
of this community occur at Great Bog (Portsmouth) and Northwood Meadows State Park (Northwood).

Red maple - sensitive fern swamps often occur as part of larger temperate minerotrophic swamp systems, and sometimes as part of temperate peat swamp systems.

Red maple - sensitive fern swamp (photo by Dan Sperduto)
Red maple - sensitive fern swamp (photo by Dan Sperduto)

Red maple - sensitive fern swamp in Newington (photo by Ben Kimball for the NH Natural Heritage Bureau)
Red maple - sensitive fern swamp in Newington
(photo by Ben Kimball)

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