Invalid Unit Specified
G597 Acer rubrum - Quercus bicolor - Fagus grandifolia Flatwoods & Swamp Forest Group

The U.S. National
Vegetation Classification
Type Concept Sentence: This is a diverse group of wooded wetland vegetation types encompassing primarily non-alluvial wetlands of the central to east-central United States and adjacent Canada, including depression swamps, ponds, and various kinds of flatwoods. Many examples are dominated by Quercus bicolor, Quercus palustris, or other oak species, or a mix of hardwoods, including Acer rubrum, Fagus grandifolia, Fraxinus spp., and Ulmus americana.
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Common (Translated Scientific) Name: Red Maple - Swamp White Oak - American Beech Flatwoods & Swamp Forest Group
Colloquial Name: Central Hardwood Flatwoods & Swamp Forest
Hierarchy Level: Group
Type Concept: This wooded wetland vegetation group encompasses various primarily non-alluvial wetlands of the central to east-central United States. It is a diverse group, containing types associated with ponds and depressions, as well as various kinds of flatwoods. Ponded examples vary from open water to herb-, shrub-, or tree-dominated. The vegetation may be zoned, with an outer ring of trees, a more interior ring of shrubs, herbs and vines, and possibly a deeper central area with or without standing water year-round depending on precipitation. Quercus species, including Quercus bicolor and Quercus palustris, dominate the canopy in many examples of this group. In addition, Acer rubrum, Acer saccharinum, Fraxinus pennsylvanica, Nyssa spp., Platanus occidentalis, Ulmus americana, or a combination of these, may dominate. Cephalanthus occidentalis is a typical shrub component in areas with a longer hydroperiod. The herbaceous layer is widely variable depending on geography and hydroperiod. In flatwoods examples, across the upper Midwest and Lower New England, Quercus bicolor and/or Quercus palustris are the common oak species. South of the glaciated Midwest (e.g., in the Ozarks), Quercus stellata is more common. Drier examples of flatwoods across the range of this group may have Acer rubrum, Fagus grandifolia, Nyssa sylvatica, Quercus alba, Quercus rubra, and Quercus velutina. Understory shrub and herbaceous species vary with moisture level and canopy density. Flooding, drought, and fire can impact examples of this vegetation. Fire is particularly important in flatwoods examples found in the south-central United States.

These wetland features are the result of topographic or edaphic circumstances that promote an enhanced hydroperiod at these sites, and this affects the vegetation and dynamics of these communities. The depressional swamps and flatwoods associations are found throughout the northern glaciated Midwest into the south-central United States ranging east into Lower New England. Stands of both types occur on flat to gently sloping to undulating surfaces, as well as in shallow to deep basins of sinkholes or other isolated depressions on uplands, as well as poorly drained uplands; glaciated examples occur in depressions associated with glacial features such as tillplains, lakeplains or outwash plains. Soils are poorly drained to very poorly drained, and surface water may be present for extended periods of time, rarely becoming dry. Soils often contain an impermeable clay layer or fragipan creating a shallow, perched water table. Saturation can vary, with ponding common during wetter seasons, and drought possible during the summer and autumn months.

The typical hydrology is seasonally flooded, but the hydroperiod may be of greater or lesser length, depending on the depth of the basin or depression feature and the annual rainfall. Water depth may vary greatly on a seasonal basis and may be a meter deep or more in the winter in longer hydroperiod examples. Some examples become dry in the summer. Soils may be deep (100 cm or more), consisting of poorly drained mineral soil, as well as of peat or muck, with parent material of peat, muck or alluvium. Microtopography and fluctuating moisture levels can lead to complexes of forest upland and wetland species occurring within this group.
Diagnostic Characteristics: These are forested, more-or-less isolated flat to depressional wetland forests of the unglaciated and glaciated interior (central Midwest) of the eastern United States. Examples are typically dominated by wetland Quercus species or by other wetland deciduous hardwood trees, or by a combination of these.
Rationale for Nominal Species or Physiognomic Features: This is a group of diverse composition and has some floristic overlap with mesic hardwood forests, as well as with floodplain wetland forests. It would be hard to have a more rigorously specific set of discriminant nominals.
Classification Comments: This group represents the merger of former Central Depression Pond Group (G169) and Central Flatwoods Group (G170), the independent existence of which can no longer be justified. Some of the landform features in which this vegetation is found have their geologic origin as a more-or-less complete karst collapse feature. Some of them may display this geologic origin in a more explicit manner, with definite walls and exposed limestone or dolomite at the surface ("sinkholes"). Others are more subtle and exist as more gentle depressions, with no exposed surface geology ("depression ponds"). Also included are associations from the sinkhole ponds of northern New Jersey (K. Walz pers. comm.) and ponds of the Ridge and Valley in Pennsylvania. These are very similar to Shenandoah sinkhole ponds of Virginia and are in Maryland as well. Southern Piedmont associations vary in relation to their underlying soil, geology, geography, and basin morphology. This variation is accounted for at the alliance and association levels. A few disjunct pond examples may occur in the Southern Blue Ridge because of similarity in topographic setting and general structure. They do, however, occur on different substrates (quartzite and sandstone) than any examples in the Piedmont. Their vegetation is different from other examples but not in having more montane flora. Their vegetation is no more different than most other pools are from each other. Most of the flatwoods and many swamp examples are found north of the glacial line in the Midwest and Lower New England. Those examples south of that range are relatively limited to broad, flat areas of the Interior Highlands.
Similar NVC Types:
G044 Central Interior-Appalachian Seepage Swamp, note: includes seepage swamps.
G037 Coastal Plain Mixed Evergreen Swamp, note: of the coastal plains.
G038 Coastal Plain Hardwood Basin Swamp, note: of the coastal plains.
G599 Central Interior-Appalachian Open Depression Pond, note:
G667 Northeastern Forest Vernal Pool, note:
Physiognomy and Structure: Stands of this group are composed of broad-leaved deciduous trees. The canopy can range from moderate to dense. The density of shrubs and herbs varies based on the extent of canopy closure, hydrologic regime, and disturbance regime.
Floristics: The vegetation of this group consists of wetland forest stands dominated by wetland Quercus species, including Quercus palustris and Quercus bicolor as well as Platanus occidentalis, Fraxinus pennsylvanica, Acer rubrum, Acer saccharinum, or Nyssa spp., or a combination of these. Cephalanthus occidentalis is a typical shrub component. Examples that have been logged or cleared may be dominated by Acer rubrum or Liquidambar styraciflua. Lower strata are generally sparse in longer hydroperiod examples. Open ponds may have the same canopy species on the edges, but a few have Nyssa sylvatica or other wetland species. The lower strata are better developed in the open pools, with Cephalanthus occidentalis, Leucothoe racemosa, Vaccinium spp., or other wetland shrubs occurring as thickets along the edge or scattered in the interior. Large Smilax tangles sometimes occur. Herbs are usually still sparse or patchy but may include dense beds or scattered clumps of various graminoids or ferns. Sphagnum moss is sometimes extensive in parts of the pools. These isolated seasonal wetlands are often important breeding sites for amphibians.

In the flatwoods of the upper Midwest and Northeast, Quercus palustris and/or Quercus bicolor typically dominate the wetter portions and are often associated with Acer rubrum. In addition, Quercus alba, Quercus rubra, Fagus grandifolia, and Acer saccharum are common in the better-drained areas. Fagus grandifolia dominates in some areas across the Midwest and Northeast. South of the glaciated Midwest into the Interior Highlands, Quercus phellos and Quercus stellata are more common. Quercus alba, Quercus rubra, and/or Quercus velutina may occur in drier examples across the range of the group. Other possible canopy species include Acer rubrum, Liquidambar styraciflua, and Nyssa sylvatica. Understory shrub and herbaceous species vary with moisture level and canopy density. Stands with greater density of tree cover have less shrub and herbaceous cover, while those with moderate tree canopy cover tend to have a dense understory. Some common species include Alnus spp., Carex spp., Cephalanthus occidentalis, Ilex spp., and Osmunda cinnamomea. Other species (in drier zones or phases) include Campsis radicans, Cardamine bulbosa, Croton willdenowii, Danthonia spicata, Leersia spp., Manfreda virginica, Porteranthus stipulatus, and Pycnanthemum tenuifolium.
Dynamics: The dynamics of water levels are the most important factor in these communities, differentiating them from the surrounding uplands and differentiating the various alliances and associations within the group. Most depressions and basins have a very limited watershed area, so water comes largely from rainfall. Variation in rainfall patterns will drive variation in duration of flooding, though most basins have an outlet that ultimately limits water depth. Fire is presumably naturally rare in these systems. Though they would naturally be exposed to fires in the surrounding uplands, standing water and lack of continuous fuel would limit fires to the edges of ponds, with greater influence in flatwoods. The migration of amphibians is presumably important as a dynamic process, as they concentrate in these areas for breeding. Ecosystem dynamics may be strongly affected by the suitability of surrounding uplands for amphibian adult habitat. Flooding and periodic drought can influence flatwoods examples; invasive shrubs are a problem in some areas. Very few flatwoods examples remain as almost all have been drained, tiled, and converted to agriculture.
Environmental Description: This group accommodates hardwood forests found in wet edaphic or topographic situations, ranging from upland flats to depressions. These are known respectively as swamps, flatwoods and ponds. They can all range in hydroperiod from short to long. Stands of this group occur in poorly drained, small, shallow to deeper basins, sinkholes, or gentle swales on flat to rolling upland sites, and occasionally in depressions on narrow, steeper ridgetops, sometimes associated with glacial features such as tillplains, lakeplains or outwash plains.

Soil/substrate/hydrology: Soils are poorly drained to very poorly drained, and have a dense clay hardpan or some other impermeable clay layer or fragipan that limits internal drainage and can create a shallow, perched water table. Some soils may be deep (100 cm or more), consisting of peat or muck, with parent material of peat, muck or alluvium. Rainwater accumulates in the basins and persists through the wet season, occasionally persisting all year. Some examples become dry, with drought possible during the summer and autumn months. These fluctuating moisture levels can lead to complexes of forest upland and wetland species occurring within this group, particularly in flatwoods. Only a few kinds of rock are known to form these depressions. Most examples occur on mafic rocks such as gabbro or diabase, but a few occur on slates or on mafic to felsic tuffs where a dense clay hardpan has formed. A few occur over bedrock of other kinds. Rock chemistry affects soil chemistry and influences variation in vegetation, but hydroperiod is a more important influence.
Geographic Range: The distribution of this group ranges from southern Minnesota, Wisconsin and Michigan across to southern Ontario and Lower New England, south to the Ozark-Ouachita region and east to Virginia.
Nations: CA, US
States/Provinces: AR, CT, DC?, DE, IA, IL, IN, KY, MA, MD, MI, MO, NH, NJ, NY, OH, ON, PA, QC, RI, TN, VA, WI, WV
US Forest Service Ecoregions (2007)
Domain Name:
Division Name:
Province Name: Southeastern Mixed Forest Province
Province Code: 231    Occurrence Status: Confident or certain
Section Name: Western Unglaciated Allegheny Plateau Section
Section Code: 221F     Occurrence Status: Confident or certain
Omernik Ecoregions: 65:C, 65e:C, 71:C, 71e:C, 71f:C, 72:C, 72a:C, 72c:C, 72h:C, 74:C, 74b:C
Plot Analysis Summary:
Confidence Level: Moderate
Confidence Level Comments:
Grank: GNR
Concept Lineage: G169 and G170 first merged into a single flatwoods and pond unit, but then split into G597 (Central Flatwoods & Pond, ~glaciated) and G654 (east-central flatwoods, ~unglaciated).
Obsolete Names:
Central Hardwood Swamp & Flatwoods Forest
Obsolete Parents:
Synonomy: > Southern Hardwood Swamp (Kost et al. 2007)
> Southern Wet-mesic Forest (Curtis 1959)
> Wet-mesic Flatwoods (Kost et al. 2007)
Concept Author(s): M. Pyne and S. Menard, in Faber-Langendoen et al. (2011)
Author of Description: M. Pyne, S. Menard and D. Faber-Langendoen
Version Date: 19Jan2016
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