Common (Translated Scientific) Name: Eastern Hemlock - Black Ash - Atlantic White-cedar Flooded & Swamp Forest Macrogroup
Colloquial Name: Laurentian-Acadian-North Atlantic Coastal Flooded & Swamp Forest
Hierarchy Level: Macrogroup
Type Concept: This swamp forest macrogroup ranges from temperate regions of northwest Ontario east to Atlantic Canada, and from central Minnesota east to northern New England. It includes deciduous and coniferous trees, including Betula alleghaniensis, Fraxinus nigra, Larix laricina, Picea rubens, Pinus strobus, Thuja occidentalis, and Tsuga canadensis to the north, and Chamaecyparis thyoides and Nyssa sylvatica to the south, with Acer rubrum usually present throughout the range and often strongly dominant in more successional stands. Occasionally, colder conditions favor Abies balsamea, Picea glauca, or Picea mariana, mixed with temperate trees, shrubs, and herbs. This macrogroup covers a wide pH range, and includes alkaline to circumneutral swamps and floodplains characterized by Fraxinus nigra, Thuja occidentalis, and Ulmus americana and acidic swamps characterized by Chamaecyparis thyoides, Picea rubens, and/or lacking Thuja occidentalis and Fraxinus nigra. Common shrubs may include Clethra alnifolia, Gaylussacia dumosa, Ilex glabra, Leucothoe racemosa, Rhododendron viscosum in the south; Alnus incana, Nemopanthus mucronatus, Viburnum nudum var. cassinoides in the north, with Ilex verticillata and Vaccinium corymbosum over much of the range. Ferns may be common, including Dryopteris cristata, Osmunda cinnamomea, Onoclea sensibilis, Thelypteris palustris, and others. Sedges and Sphagnum mosses are common. Hummock-and-hollow microtopography is characteristic, and trees are often primarily confined to hummocks, with more hydrophytic herbaceous vegetation in hollows. These swamps form in basin wetlands that remain saturated for all or nearly all of the growing season, and may have standing water seasonally. Some occur on gently sloping seepage lowlands, and even basin settings may have some seepage influence, especially near the periphery.
Diagnostic Characteristics: Saturated forests with prominent canopy trees including Acer rubrum and associates Chamaecyparis thyoides or Pinus rigida occurring on the Atlantic Coastal Plain from Virginia to southern New England, or Acer rubrum, Betula alleghaniensis, Fraxinus nigra, Larix laricina, Picea rubens, Thuja occidentalis, and Tsuga canadensis inland and to the north. The shrub and herbaceous layers have a significant component of hydrophytes (facultative to obligate wetland species). Ferns are prevalent within these swamp forests, including Dryopteris cristata, Osmunda cinnamomea, Onoclea sensibilis, Thelypteris palustris, and others.
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: Some species, such as Clethra alnifolia, Gaylussacia dumosa, and Ilex glabra, have coastal plain affinities.
Similar NVC Types:
M029 Central Hardwood Floodplain Forest, note: has floodplain trees such as Acer saccharinum, Betula nigra, Quercus palustris, and Platanus occidentalis.
M302 Eastern North American Ruderal Flooded & Swamp Forest, note:
M503 Central Hardwood Swamp Forest, note: occurs to the south and west and is characterized by presence of Liquidambar styraciflua, Liriodendron tulipifera, Quercus phellos, and flatwoods species Quercus palustris and Quercus bicolor in addition to Acer rubrum; lacks northern conifers Picea rubens, Thuja occidentalis, and lacks Chamaecyparis thyoides or Pinus rigida.
Physiognomy and Structure: Deciduous, mixed, or coniferous canopy ranging from dense to partially open; shrub layer generally well-developed but can be sparse under dense canopy and where deer browse pressure is high. Hummock-and-hollow microtopography is characteristic, and mosses, especially species of Sphagnum, are common and usually abundant. Hummocks and decaying nurse logs provide critical substrate for plant establishment and growth.
Floristics: Acer rubrum is a relatively constant species throughout the range of these swamps. At the northern end of the range, canopy trees Betula alleghaniensis, Larix laricina, Picea rubens, Pinus strobus, and Tsuga canadensis are characteristic. Nyssa sylvatica can be more important toward the southern end of the range. Occasionally, colder conditions favor Abies balsamea, Picea glauca, or Picea mariana, mixed with temperate trees, shrubs, and herbs. Typical shrubs include Alnus incana, Carpinus caroliniana, Cornus spp., Ilex verticillata, Lindera benzoin, Nemopanthus mucronatus, Ribes spp., Rubus pubescens, Salix spp., Vaccinium corymbosum, and Viburnum nudum var. cassinoides. On the coastal plain, Picea rubens and Larix laricina are replaced by Chamaecyparis thyoides or Pinus rigida, with typical shrubs including Clethra alnifolia, Gaylussacia dumosa, Ilex glabra, Leucothoe racemosa, and Rhododendron viscosum. Typical herbs across the range of acidic swamps include Carex folliculata, Carex intumescens, Carex scabrata, Carex stricta, Chelone glabra, Dryopteris cristata, Onoclea sensibilis, Osmunda spp., Saxifraga pensylvanica, and Symplocarpus foetidus, among others. Alkaline swamps are limited to the northern portion of the range of this macrogroup and are characterized by Acer rubrum, Fraxinus nigra, Larix laricina, Thuja occidentalis, and Ulmus americana, with shrubs including Rhamnus alnifolia and Cornus sericea in addition to the shrubs of northern acidic swamps. Herbaceous species of alkaline swamps include Caltha palustris, Carex bromoides, Carex leptalea, Geum rivale, Impatiens capensis, and Packera aurea, in addition to many of the acidic swamp species listed above.
Dynamics: From Slaughter et al. (2007): "The primary natural processes structuring hardwood-conifer swamp are small-scale windthrow and dynamics of surface water and groundwater. Patchy windthrow is the dominant natural disturbance, creating small-scale canopy gaps (Forrester et al. 2005).
"Seedlings of several characteristic hardwood-conifer swamp canopy species (e.g., yellow birch, white pine, northern white-cedar, and hemlock) preferentially germinate and establish on root hummocks and/or decaying logs versus muck or litter-covered depressions (i.e., hollows) (Holcombe 1976, St. Hilaire and Leopold 1995, Rooney and Waller 1998, Allison and Ehrenfeld 1999, McGee 2001, Rooney et al. 2002). In comparison to hollows, hummocks and decaying logs have high moss cover, high moisture content, coarse substrate texture, and stable hydrology, characteristics which may favor the germination and establishment of small seeds with low nutrient reserves (Coffman 1978, St. Hilaire and Leopold 1995, McGee 2001).
"Groundwater and surface water dynamics also shape hardwood-conifer swamp structure and impact succession. Significant hydrological processes impacting hardwood-conifer swamp include groundwater seepage, water table fluctuation, seasonal inundation, and flooding events. "
Logging, especially of Thuja occidentalis and Chamaecyparis thyoides, has influenced the structure and dominance of this macrogroup. Regeneration of Chamaecyparis thyoides is stimulated by fire.
At the present time, excessive deer herbivory threatens the viability of hardwood-conifer swamp throughout its range. High white-tailed deer (Odocoileus virginianus) density is leading to considerable browse pressure on conifer seedlings and saplings throughout Michigan and the Great Lakes region (Frelich and Lorimer 1985, Mladenoff and Stearns 1993, Alverson and Waller 1997, Long et al. 1998, Rooney and Waller 1998, Rooney et al. 2002, Krueger and Peterson 2006). Deer browse also reduces frequency and cover of understory shrubs and herbs (Balgooyen and Waller 1995, Augustine and Frelich 1998, Rooney and Waller 2003, Kraft et al. 2004). The result of heavy deer browse is significant alteration of community structure consisting of impacts to all vegetative strata.
Environmental Description: From Slaughter et al. (2007): "Hardwood-conifer swamp occurs on a variety of landforms, including poorly-drained outwash channels and outwash plains and depressions on medium- to coarse-textured end moraines, ground moraines, and glacial lakeplains (Kost et al. 2007). The community occupies sites influenced by groundwater seepage, usually where the water table is at or near the soil surface. Hardwood-conifer swamp occurs on gently sloping to flat topography along headwater streams or in association with relatively inactive portions of floodplains of low order streams, where it forms backswamps or occurs in meander scars (Tepley et al. 2004). Shallow kettle depressions and the margins of large forested and non-forested peatlands may also support hardwood-conifer swamp, but the community is absent from areas where significant peat accumulation isolates the rooting zone from contact with mineral-rich groundwater." The type may also occur in floodplains. The substrate is either wet mineral soils or peat, and hummocky topography is present. The groundwater ranges from low to high base status.
Geographic Range: This macrogroup ranges from New England west to Minnesota, south along the Appalachian Mountains to Virginia, and east to the Atlantic Coastal Plain.
Nations: CA, US
States/Provinces: CT, DE, IL, IN, MA, MD, ME, MI, MN, NB, NH, NJ, NS, NY, OH, ON, PA, QC, RI, VA, VT, WI, WV
|US Forest Service Ecoregions (2007)|
Outer Coastal Plain Mixed Forest Province
Confident or certain
White Mountains Section
Confident or certain
Confidence Level: Moderate
Confidence Level Comments:
Synonomy: >< Atlantic white cedar wetland (Laderman 1989)
< Northern White-Cedar - Hemlock - Red Spruce Conifer Swamp Group (Faber-Langendoen and Menard 2006)
>< Red maple swamp (Golet et al. 1993)
>< Spring swamp (National Wetlands Working Group 1988)
Concept Author(s): Faber-Langendoen et al. (2014)
Author of Description: L. Sneddon and C. Lea
Acknowledgements: Sue Gawler authored two groups contributing to this description. Josh Cohen provided additional edits and the extended quoted text from Slaughter et al. (2007). Sean Basquill provided review comments.
Version Date: 05Jun2015
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