Black gum - red maple basin swamp (S3)
3. Hemlock forest/woodland variant:
Black gum - red maple basin swamps are an uncommon wetland type in New England. They are very similar in vegetation, soils, and hydrology to red maple - Sphagnum basin swamps. A principal distinction between the two is the co-dominance of black gum (Nyssa sylvatica) with red maple (Acer rubrum) in the canopy of this community. These swamps typically occur in perched upland till basins with watersheds smaller than one square mile. Species typical of acidic, relatively stagnant conditions are prevalent, but these swamps are highly variable in structure and composition, ranging from forest (greater than 60% tree cover) to sparse woodland (10–25% tree cover). The shrub layer density increases in woodland and sparse woodland examples. Historical logging activities may also have influenced the structure and composition of some examples, and additional research on stand history is needed to clarify the relationships between land use history and current vegetation.
These swamps contain the highest concentrations of black gum trees of any habitat in New England. Black gum is tolerant of nutrient-poor, swampy conditions, and persists by outlasting other species. The craggy, stag-headed crowns and deeply furrowed bark of old black gum are a notable feature of this community.
Soils are typically acidic, nutrient-poor, very poorly drained Histosols (deep peat or muck) or poorly to very poorly drained mineral soils with histic epipedons. Peat is well decomposed near the surface, and pHs average approximately 4.4 (range: 3.7–5.3). Hummocks are well developed and average approximately 0.4 m high. There is little evidence of seepage or surface water flow in black gum swamps. Examples in lakeside settings may be influenced somewhat by surface flow, but water sources are generally restricted to precipitation, seasonal runoff or subsurface flow from surrounding uplands. Many of these swamps have stagnant outlet streams but no perennial inlets or streams running through them; others have neither inlets nor outlets.
Characteristic vegetation: In most cases, black gum and red maple dominate the tree canopy, with varying but smaller contributions by other hardwood and softwood species. Highbush blueberry (Vaccinium corymbosum) and winterberry (Ilex verticillata) are the primary shrub layer dominants, with a variable component of other tall and medium-height shrub species. The winterberry plants produce bright red berries in fall that provide an excellent food source for birds. Cinnamon fern (Osmunda cinnamomea) is usually abundant in the herb layer, which consists of acidic wetland or moist-site species in hollows and drier-site species on hummocks. The herbaceous plant layer is mostly composed of several trailing evergreen species such as partridgeberry (Mitchella repens) and wintergreen (Gaultheria procumbens), as well as others such as bunchberry (Cornus canadensis), cinnamon fern (Osmunda cinnamomea), and several sedges. Sphagnum mosses often form a patchy to dense layer, particularly in hollows and on the lower sides of hummocks. Peat moss on the ground is saturated year-round.
Variants: Four variants are described, relating mostly to woody structure:
1. Boggy woodland/tall shrub thicket variant:
This variant includes swamps with a woodland or sparse woodland canopy and with a well developed tall shrub layer, a sparse to moderate herbaceous layer, and moderate to dense Sphagnum moss cover. The more open woodland or tall shrub structure, and frequency of hydrophytic species such as Sphagnum torreyanum and Carex canescens (silvery sedge), may indicate a wetter hydroperiod than in other variants. Most lakeside occurrences of this community correspond to this variant.
Minor amounts of Picea rubens (red spruce) and Tsuga canadensis (hemlock) may be found in the canopy or understory. Sphagnum moss predominates in the wetter hollows and hummock-sides of this variant and species include abundant Sphagnum magellanicum; S. torreyanum, a predominantly aquatic, coastal plain species, is locally dominant in hollows. These species are indicative of oligotrophic to weakly minerotrophic conditions.
2. Boggy forest/woodland variant:
This variant has a variable forest or woodland tree canopy of black gum and red maple, frequently with red spruceand/or Pinus strobus (white pine) in the canopy and/or subcanopy. Hemlock and Betula alleghaniensis (yellow birch) are typically restricted to the understory. The shrub and herbaceous layers are highly variable but usually well developed and on average shorter than in the boggy woodland/tall shrub thicket variant. Sphagnum mosses are more abundant on average than in other variants, and the species composition is indicative of more acidic, nutrient-poor conditions than that found in the hemlock forest/woodland variant, giving examples a more “boggy” character.
Sarracenia purpurea (pitcher-plant) occurs only occasionally, but its presence can help distinguish this variant from the hemlock forest/woodland variant described below. Sphagnum mosses typically form a relatively dense carpet and the types present are indicative of oligotrophic to weakly minerotrophic conditions. These include Sphagnum fallax, S. angustifolium, and/or S. magellanicum.
This variant has a forest or woodland structure with a strong hemlock component in the canopy and/or subcanopy. Yellow birch and white pine are typical in the understory. While variable, the shrub layer is sparser on average in this variant than the previous two. Sphagnum is generally of moderate density, and consists of species indicative of more minerotrophic conditions than are present in the more “boggy” black gum swamp variants. These include Sphagnum flexuosum, S. affine, S. centrale, S. henryense, S. fimbriatum, S. palustre, and S. recurvum. Other Sphagnum species in this variant include S. angustifolium, S. magellanicum, S. torreyanum, S. fallax, and S. cuspidatum indicative of oligotrophic to weakly minerotrophic conditions. Other bryophytes are also more frequent in this variant. Additional minerotrophic indicators that are occasional in this variant include Osmunda regalis (royal fern), Chelone glabra (white turtlehead), and Fraxinus nigra (black ash).
4. Mountain laurel variant:
This variant is indicated by a dominant layer of mountain laurel in some swamps of southwest NH.
Good examples of this community occur at Five Finger Point (Holderness),
Black gum - red maple basin swamps often occur as part of temperate peat swamp systems, and occasionally as part of coastal conifer peat swamp systems.
3. Hemlock forest/woodland variant:
Black gum - red maple basin swamp at Pawtuckaway State Park (photo by Ben Kimball)
Deeply-furrowed bark of an old black gum tree in Pisgah State Park (photo by Ben Kimball)
Black gum is a widespread tree of upland and lowland habitats in eastern North America. It occurs in small, nutrient-poor swamps perched on hillside benches, along lake shores, and less often on floodplains or in upland forests adjacent to wetlands. The species rarely attains dominance in any community, except in swamps at the northern edge of its range in New Hampshire and other nearby states.
Black gum grows slowly, and thus requires few nutrients. As a result it us able to survive in the nutrient-poor settings of many basin swamps. On average, black gum adds less than a millimeter of girth each year. Black gum is also shade-tolerant, capable of growing readily after long periods of shade suppression, and can sprout from a clonal root system or seed. The laterally extensive root network resulting from its clonal nature increases the tree’s resistance to windthrow. In addition, the species is flood, fire, and drought tolerant. In short, black gum endures because it is both resilient and resistant to a broad range of environmental stresses. Importantly, black gum wood also has little timber value, an attribute that has saved the species from harvesting.
two very old black gum trees (photo by Dan Sperduto)
See also: NH Heritage's 2000 report on Black Gum in New Hampshire