Common (Translated Scientific) Name: Swamp Chestnut Oak - Bald-cypress - Pecan Southern Floodplain Forest Macrogroup
Colloquial Name: Southern Coastal Plain Floodplain Forest
Hierarchy Level: Macrogroup
Type Concept: These floodplain forests are found in the southern United States, in the Atlantic and Gulf coastal plains from Delaware to Texas and in adjacent interior provinces, north to southeastern Missouri, southern Illinois, southern Indiana, and western Kentucky. There are three broad combinations of dominant species that collectively constitute the vegetation of this macrogroup: bald-cypress - tupelo forests (G033), oak - sweetgum forests (G034), and ash - elm - willow forests (G759). The dominant species in stands of floodplain forest primarily vary with hydroperiod, with species sorting on a rough gradient from wet to mesic. Bald-cypress - tupelo forests (G033) are primarily dominated by Taxodium distichum (occasionally Taxodium ascendens) with Nyssa aquatica (occasionally Nyssa biflora). Oak - sweetgum forests (G034) are dominated by Liquidambar styraciflua, Quercus spp., and Ulmus spp. There is also some floristic variation based on hydrology; shorter- hydroperiod examples will contain Quercus michauxii, Quercus pagoda, and Quercus shumardii, and longer-hydroperiod ones will have Nyssa biflora, Quercus laurifolia, Quercus lyrata, and Quercus phellos. Other dominant species include Acer negundo, Celtis laevigata, Fraxinus pennsylvanica, and Platanus occidentalis. Ash - elm - willow forests (G759) are typically dominated by Fraxinus pennsylvanica, Populus deltoides, Salix caroliniana, Salix nigra, and Ulmus americana. Except in the very wet examples, understory, shrub and herb layers are generally well-developed and woody vines are also prominent. Vines such as Nekemias arborea, Berchemia scandens, Campsis radicans, Parthenocissus quinquefolia, and Vitis spp., may be conspicuous. Arundinaria gigantea is a common understory component in these forests on natural levees and higher point bars, and may become dominant after thinning or removal of the overstory. These are communities of streams and rivers of all orders and sizes, including some tidal forests. Stands are typically flooded for periods of up to 3 months, but not during the growing season. Stands are known from low bottomlands, depressions, sloughs and abandoned channel segments, as well as from elevated features such as riverfronts, point bars, natural levees, high bottomlands, ridges, and upper terraces. This floristic and ecological variation is accounted for at the group and alliance levels. Some examples of these forests are known as "blackwater" and others as "brownwater."
Diagnostic Characteristics: These are all floodplain forests of the southern United States, dominated by a variety of distinctive species which are found only, or primarily, in stands of this macrogroup. Probably the most strongly diagnostic species include Acer rubrum var. drummondii, Carya aquatica, Fraxinus profunda, Gleditsia aquatica, Nyssa aquatica, Nyssa biflora, Planera aquatica, and Taxodium distichum (in longer hydroperiod examples), and Carpinus caroliniana, Liquidambar styraciflua, Platanus occidentalis, Populus deltoides, Quercus laurifolia, Quercus lyrata, Quercus michauxii, Quercus nigra, Quercus phellos, Quercus pagoda, Quercus shumardii, and Quercus texana (in shorter hydroperiod examples).
Rationale for Nominal Species or Physiognomic Features: There are many dominant tree species among which to choose. Quercus michauxii represents the mesic end of the hydrologic spectrum, Taxodium distichum the wetter end, and Carya illinoinensis, represents the western extension into the great plains. Its natural range barely crosses the Mississippi River. These species' geographic ranges collectively represent the range of this macrogroup, and they have appropriate environmental preferences.
Classification Comments: Some embedded patches of smaller trees, including Cornus foemina, Forestiera acuminata, Itea virginica, and Planera aquatica, are also included here, as are patches of Cephalanthus occidentalis, which can range in lifeform from small tree to shrub. These are usually smaller-patch features imbedded within larger-patch (and taller stature) floodplain forests of various types. The basis of the distinction among the groups in this macrogroup is floristic and broadly ecological rather than purely hydrologic. Isolated wetlands such as depression ponds dominated by Taxodium are placed in nonriverine groups. Forests dominated by Fagus grandifolia with or without Magnolia grandiflora belong in mesic groups, whether they are clearly in uplands or in upland-floodplain transition areas.
Along the western edge of the range of Southern Coastal Plain Floodplain Forest Macrogroup (M031) in Texas and Oklahoma, it transitions into the single group in Southern Great Plains Floodplain Forest & Woodland Macrogroup (M154), i.e., Southeastern Great Plains Floodplain Forest Group (G784). While there is some floristic overlap between these two macrogroups, M154 lacks many of the eastern species characteristic of M031.
Similar NVC Types:
M032 Southern Coastal Plain Evergreen Hardwood - Conifer Swamp, note:
M033 Southern Coastal Plain Basin Swamp & Flatwoods, note: is found in nonriverine settings and shares some species.
M154 Southern Great Plains Floodplain Forest & Woodland, note:
M310 Southeastern North American Ruderal Flooded & Swamp Forest, note: contains exotic tree species and generalist native tree species on strongly human disturbed sites.
M036 Interior Warm & Cool Desert Riparian Forest, note:
Physiognomy and Structure: These are most typically closed-canopy flooded, riverine, and bottomland forests (and more rarely woodlands) dominated by a combination of tall broad-leaved deciduous trees and a needle-leaved deciduous tree (Taxodium). The understory is also quite variable. Shrubs and herbaceous plants can be virtually absent to dense. Vines are common.
Floristics: The dominant species in stands of floodplain forest primarily vary with hydroperiod, with species sorting on a rough gradient from wet to mesic. Bald-cypress - tupelo forests (G033) are primarily dominated by Taxodium distichum (occasionally Taxodium ascendens) with Nyssa aquatica (occasionally Nyssa biflora). Oak - sweetgum forests (G034) are dominated by Liquidambar styraciflua, Quercus spp., and Ulmus spp. There is also some floristic variation based on hydrology; shorter- hydroperiod examples will contain Quercus michauxii, Quercus pagoda, Quercus shumardii, and Quercus texana and longer-hydroperiod ones will have Nyssa biflora, Quercus laurifolia, Quercus lyrata, and Quercus phellos. Other dominant species include Acer negundo, Celtis laevigata, Fraxinus pennsylvanica, and Platanus occidentalis. Ash - elm - willow forests (G759) are typically dominated by Fraxinus pennsylvanica, Populus deltoides, Salix caroliniana, Salix nigra, and Ulmus americana.
Some other trees which may be associated with stands of this group include Acer rubrum var. drummondii, Carya aquatica, Fraxinus pennsylvanica, Gleditsia aquatica, Salix nigra, and other trees tolerant of flooding. Some inclusions are dominated by small trees or large shrubs, including Carpinus caroliniana, Cephalanthus occidentalis, Cornus foemina, Decodon verticillatus, Forestiera acuminata, Ilex decidua, Ilex opaca var. opaca, Itea virginica, Planera aquatica, and Viburnum dentatum. Except in the very wet examples, understory, shrub and herb layers are generally well-developed and woody vines are also prominent. Vines such as Nekemias arborea (= Ampelopsis arborea), Berchemia scandens, Campsis radicans, Parthenocissus quinquefolia, Smilax bona-nox, Toxicodendron radicans, and Vitis spp., may be conspicuous. The perennial graminoid bamboo Arundinaria gigantea (= ssp. gigantea) is a common understory component in these forests on natural levees and higher point bars, and may become dominant after thinning or removal of the overstory. Some other examples have very diverse herbaceous layers, including Bidens aristosa, Carex cherokeensis, Carex debilis, Carex digitalis, Carex joorii, Chasmanthium latifolium, Geum canadense, Glyceria striata, Leersia virginica, and Polygonum hydropiperoides. Terrestrial herbs in wetter examples are usually limited due to long hydroperiods, and are often only found on elevated logs and stumps, but can include Boehmeria cylindrica, Carex decomposita, Carex grayi, Carex intumescens, Carex joorii, Carex lupulina, Commelina virginica, Leersia lenticularis, Onoclea sensibilis, and Saururus cernuus. Aquatic and floating herbs include Ceratophyllum spp., Elodea spp., Lemna minor, Ludwigia peploides, Potamogeton spp., and Sagittaria lancifolia.
Floodplain forests, at least in the Southern Appalachian region, are much more prone to invasion from exotics than are uplands, with average cover of 22% (Brown and Peet 2003). Matthews et al. (2011) note the following exotics are common in Piedmont floodplain forests: shrubs Ligustrum sinense, Lonicera japonica; and herbs Glechoma hederacea, Microstegium vimineum, Murdannia keisak. Additional information is needed on the typical exotics found in this macrogroup. See ~Southeastern North American Ruderal Flooded & Swamp Forest Macrogroup (M310)$$ for a summary of exotic species that may also occur in this type.
Dynamics: Flooding is an important ecological factor in examples of this macrogroup, and the length of the flooding may be the most important factor distinguishing this vegetation. In addition to disturbance, floods bring nutrient input, deposit sediment, exclude non-flood-tolerant species and disperse plant seeds. Flooding is most common in the winter but may occur in other seasons. The small flows, low gradient, and binding of sediment by vegetation limit channel shifts and sediment movement, but floods may cause local disturbance by scouring. Flood waters may have significant energy in higher-gradient systems, but scouring and reworking of sediment rarely affect more than small patches. Most of these forests would exist naturally as multi-aged old-growth forests driven by gap-phase regeneration.
Most of these forests exist naturally as multi-aged old-growth forests driven by gap-phase regeneration. Windthrow is probably the most important cause of gaps, as wind disturbance is perhaps more important than in uplands because of frequently wet soils, less dense soils, and more shallow-rooted trees.
Fire does not appear to be a dominant factor in this floodplain vegetation, and it is not very flammable. Fire is probably more important in small stream examples than in larger river ones, because distances to uplands are short and stream channels and sloughs are smaller and less effective as firebreaks. However, most of the vegetation is not very flammable and usually will not carry fire. However, historical references to canebrakes dominated by Arundinaria gigantea suggest that at least in some portions of stands, fire may have once been more of a factor. Examples often have limited herbaceous layers, making fire less important, even during extended dry periods.
Some tidal examples are included in ~Bald-cypress - Tupelo Floodplain Forest Group (G033)$$; these are affected by diurnal tidal flooding or by storm tides. In these cases, infrequent intrusion of saltier water, which is stressful or fatal to many of the plant species, is an important periodic disturbance created by storms. Natural fire is not frequent in these tidal examples, but may sometimes be important in determining the boundary between tidal swamps and tidal marshes. The tidal forest examples generally appear to be in a shifting relationship with adjacent tidal freshwater marshes. Many of these tidal marshes have standing dead trees in them, suggesting they recently were swamps. But some marshes are being invaded with trees and may be turning into swamps. Rising sea level is causing more inland swamps to develop tidal characteristics and causing some stands to turn into marshes. In areas not too strongly affected by salt intrusion, drowning by rising sea level, or fire, the communities can be expected to exist as old-growth, multi-aged forests.
Southern ash - elm - willow floodplain forests (G759) are subject to frequent disturbances, including flooding, erosion, and deposition of sediment. This leads to a physiognomically diverse group. Stands that have recently been subjected to severe flooding may be relatively open. Most stands have moderate to closed tree canopies, though.
Matthews et al. (2011), in their summary of historic changes to Piedmont floodplain forests, capture much of what has occurred across the range of this type; namely, that these forests occur in a highly fragmented landscape, where the natural hydrologic regime has been altered by anthropogenic activities for hundreds of years, where a long history of selective tree harvesting has reduced the abundance of certain species; and where non-native invasive species are increasingly common. Finally, they note that, in the Piedmont, extensive sediment deposition occurred following European agriculture on the uplands during the period 1700-1940.
Environmental Description: This vegetation occurs on and near streams and rivers of all orders and sizes, including tidal forests. Sites include floodplains and terraces affected by river flooding and on emergent bars and banks within channels. Depositional landforms, including levees, sloughs, ridges, terraces, and abandoned channel segments may be present within stands. The substrate is primarily alluvium. Soils are usually sandy to loamy, but include local clayey and gravelly areas. Soils are generally fertile. Alluvial soils may be as important a factor as ongoing flooding in differentiating this vegetation from that of adjacent uplands. Emergent and vegetated bars of gravel to cobbles occur occasionally but are generally not extensive or as distinctive as they are on larger rivers. Floods are generally of short duration, and wetness is a major influence, especially within channels and where water is ponded in local depressions. The geologic substrate may be of any kind, but areas on Triassic sediments tend to have large floodplain systems even on fairly small streams.
Tidally influenced examples occur in lower reaches of river floodplains and along estuary shorelines, in places regularly or irregularly flooded by lunar or wind tides. The water has little salt content, due to distance from the ocean and/or strong freshwater input. Soils may be mineral or organic. Soils are generally permanently saturated even when the tide is low. The transition of the hydrology to flood dominance rather than tidal dominance may be very gradual.
Blackwater examples occur in floodplains of small streams of the coastal plain that carry little mineral sediment. These streams have their headwaters in sandy portions of the coastal plain. The water is usually strongly stained by tannins but has little suspended clay and is not turbid. Depositional landforms may be absent or may be present in limited variety and of small size. Soils are generally sandy in drier portions of the floodplain, mucky in wetter portions, or may be uniform organic soils. Soils are usually strongly acidic, but spring-fed rivers may have calcareous water and non-acidic soils. Flooding ranges from semipermanent in the wettest floodplains to intermittent and short in higher-gradient streams. Some small blackwater streams have most of their flow from sandhill seepage and have limited fluctuation in water levels.
In contrast, brownwater or redwater river examples occur in floodplains of medium to small coastal plain rivers that carry significant mineral sediment. These rivers have their headwaters in the Piedmont, Blue Ridge, Interior Plateaus, or in portions of the coastal plain where fine-textured sediment predominates. The water generally carries substantial amounts of silt, clay, and sometimes sand. Depositional landforms such as point bars, natural levees, backswamps, and ridge-and-swale systems (scrollwork) are well-developed and form patterns of significant variation in flooding duration and nutrient input. Soil texture varies from sandy to clayey. Soils are generally fertile and not strongly acidic. Flooding ranges from semipermanent in the wettest areas to intermittent and short on the higher portions of the floodplain. The highest terraces may no longer flood at all and will be occupied by upland vegetation.
Geographic Range: These deciduous floodplain or swamp forests are found throughout the Atlantic Coastal Plain from Delaware, New Jersey, and Virginia south to southeastern Georgia, in the Gulf Coastal Plain from Georgia to Texas, in portions of the adjacent Piedmont and interior regions from Alabama and Tennessee to southern Virginia, as well as in the Mississippi River Alluvial Plain and adjacent Upper East Gulf Coastal Plain from southeastern Missouri, southern Illinois, southern Indiana, and Kentucky south to Mississippi and Louisiana. There is also one association in the Ouachitas of Arkansas and Oklahoma. Some of the ash - elm - willow floodplain forest associations (G759) are more northerly, ranging to New York and Connecticut, but these are close to the ocean (i.e., tidally-influenced).
States/Provinces: AL, AR, CT, DC, DE, FL, GA, IL, IN, KY, LA, MA, MD, MO, MS, NC, NJ, NY, OK, PA?, SC, TN, TX, VA, WV
|US Forest Service Ecoregions (2007)|
Southwest Plateau and Plains Dry Steppe and Shrub Province
Confident or certain
White and Black River Alluvial Plains Section
Confident or certain
Confidence Level: Moderate
Confidence Level Comments:
Synonomy: > Black Willow: 95 (Eyre 1980)
> Floodplain Hardwood Forest (Marks and Harcombe 1981)
> Floodplain Hardwood Pine Forest (Marks and Harcombe 1981)
< Southern Floodplain Forests (Sharitz and Mitsch 1993)
> Swamp Cypress Tupelo Forest (Marks and Harcombe 1981)
Concept Author(s): R.R. Sharitz and W.J. Mitsch (1993)
Author of Description: M. Pyne and J. Teague
Acknowledgements: We have incorporated significant descriptive information previously compiled by J. Teague.
Version Date: 15Jun2015
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