Common (Translated Scientific) Name: Sweetbay - Swamp Bay - Pond Pine Swamp Forest Macrogroup
Colloquial Name: Southern Coastal Plain Evergreen Hardwood - Conifer Swamp
Hierarchy Level: Macrogroup
Type Concept: This macrogroup is found in the Southeastern Coastal Plain from southeastern Virginia to eastern Texas. It occurs on poorly drained, organic soil flats and seepage-fed wetlands in dissected coastal plain landscapes. It may also occur in poorly developed upland drainages and small headwater streambottoms, as well as on toeslopes. These areas are saturated by rainfall and seasonally high water tables without influence of river or tidal flooding. The vegetation is characterized by an overstory that generally includes some combination of Acer rubrum, Liriodendron tulipifera, Magnolia virginiana, Nyssa sylvatica, Nyssa biflora, Persea palustris, and Pinus serotina, although there is some variation according to latitude. Some associations may contain Chamaecyparis thyoides, but this species is not diagnostic of this macrogroup. Understory vegetation throughout the region consistently supports the vine Smilax laurifolia, and there may be ferns such as Osmunda cinnamomea, Osmunda regalis var. spectabilis, Woodwardia areolata, and Woodwardia virginica. Soils may be wet sands or mixtures of organic (peaty) and mineral soils, which are often extremely nutrient-poor. When these communities are associated with streams, they tend to be low-gradient, with narrow, often braided channels and diffuse drainage patterns.
Diagnostic Characteristics: This macrogroup contains floristically and structurally diverse wetland forests with open to closed canopies. The broad-leaved evergreen tree growth form is more dominant here than in other related types (i.e., ~Coastal Plain Hardwood Basin Swamp Group (G038)$$, ~Nonriverine Wet Oak Flatwoods Group (G130)$$), although not all examples will be so dominated. Other codominant growth forms include broad-leaved evergreen shrubs and evergreen needle-leaved trees. The component characteristic taxa are tolerant of groundwater seepage, but not long-hydroperiod flooding by deep water. Dominant taxa are typically strongly restricted to wetlands of the Southeastern Coastal Plain. Hydrology includes wet flats and gentle slopes, with groundwater rather than overbank flooding being the source of the water.
Rationale for Nominal Species or Physiognomic Features: The nominals are Southeastern Coastal Plain evergreen (broad-leaved and needle-leaved) wetland trees.
Classification Comments: Some closely related southern Chamaecyparis thyoides vegetation also is included in this macrogroup. Tree and tall-shrub pocosins are included here, but low-shrub and herb pocosins are treated in Southeastern Coastal Pocosin & Shrub Bog Group (G186) in Southeastern Coastal Bog & Fen Macrogroup (M065). Baygall wetlands are included here.
Some authors have treated Persea palustris (of wetlands) and Persea borbonia (of coastal uplands) as one taxon under a broadly conceived Persea borbonia. We recognize the two distinct taxa, following recent authors (Godfrey 1988, Kartesz 1999, Weakley 2008).
Similar NVC Types:
M031 Southern Coastal Plain Floodplain Forest, note:
M033 Southern Coastal Plain Basin Swamp & Flatwoods, note: is not dominated by broad-leaved evergreen trees or shrubs.
M310 Southeastern North American Ruderal Flooded & Swamp Forest, note:
M065 Southeastern Coastal Bog & Fen, note:
Physiognomy and Structure: Stands of this macrogroup are wetland forests with generally closed canopies and the characteristic presence or dominance of several broad-leaved evergreen tree species. In some cases the hydrology is strongly influenced by groundwater seepage, but many examples are ombrotrophic, rain fed wetlands.
Floristics: The vegetation of this macrogroup is dominated by woody plants, primarily trees. An open to closed canopy is usually present and consists of a mixture of acidic-tolerant wetland trees such as Acer rubrum, Liriodendron tulipifera, Magnolia virginiana, Nyssa sylvatica, Nyssa biflora, Persea palustris, and Pinus serotina. Some associations may contain Chamaecyparis thyoides, but this species is not diagnostic of this macrogroup. There is generally a dense shrub layer that is dominated by species shared with pocosins or baygalls, such as Arundinaria tecta (= Arundinaria gigantea ssp. tecta), Clethra alnifolia, Cliftonia monophylla, Cyrilla racemiflora, Ilex glabra, Leucothoe axillaris, Lyonia ligustrina, and Lyonia lucida, but includes some species which occur in other saturated wetlands, such as Morella caroliniensis, Persea palustris, Toxicodendron vernix, and Viburnum nudum. The vine Smilax laurifolia may be abundant. The herb layer, if well-developed at all, generally consists of large wetland ferns, such as Osmunda cinnamomea, Osmunda regalis var. spectabilis, Woodwardia virginica, and Woodwardia areolata, with Carex spp. There is some variation according to latitude, with southerly examples generally consisting of broad-leaved evergreen forests, while more northerly examples support more mixed evergreen-deciduous forests. In addition, broad-leaved evergreen species are especially pronounced in the shrub layer of southern examples.
Dynamics: The evergreen seepage-influenced vegetation types included here are quite heterogeneous in composition and in the role of fire, as well as extensive in geographic range. The streamhead seepages of the sandhills of the Carolinas, Georgia, Florida, and southern Virginia are distinctive in being strongly fire-dominated, having Pinus spp. as a major canopy dominant, and having many shrubs typical of pocosins. A second set of associations ranging from South Carolina through the Gulf Coastal Plain has vegetation that suggests less influence by fire, including hardwood canopies and shrub layers of broad-leaved evergreen shrubs of saturated habitats. A third set, from a wider variety of topographic settings throughout the region, has hardwood canopies and shrub and herb layers with less peatland affinities, more closely related to floodplain communities. Their flora suggests a minor role for fire. Fire is important, but the fire regime appears to be somewhat variable or unclear, because some of the characteristic trees are fire-intolerant (e.g., Magnolia), while others are fire-dependent (Pinus serotina). Fire frequency is lengthened by the wetness of the soil. This vegetation occurs in landscapes that had frequent fire under natural conditions, but the wetness sometimes limited fire spread, creating a less frequent fire-return interval. Natural fire intensity varies among alliances and associations, with some readily producing intense fire when they burn, while others probably experiencing only low-intensity fires because of low flammability. Persea palustris is suffering the effects of a beetle-borne fungus which is killing these trees in stands of this vegetation as well as upland maritime forests. This fungus (Ophiostoma sp.) is carried by the redbay ambrosia beetle (Xyleborus glabratus), introduced from Asia.
Environmental Description: This vegetation is found on coastal plain terrain on sites saturated by seepage of shallow groundwater. Seasonal to permanent saturation combined with wildland fire of only moderate to low frequency and woody vegetation are the unifying characteristics of this macrogroup. Often, a small stream drains the site, but overbank flooding is a negligible influence. Some examples are on wet flats, some are in bottoms of ravines, but some are on sideslopes or flats at the base of slopes. Most examples are in sandy areas where rapid soil drainage in the surrounding landscape supplies the seepage. Soils within the macrogroup itself are generally mucky sands or clay, or deeper organic soils.
Geographic Range: This vegetation ranges from southeastern Virginia to eastern Texas, extending into central Florida and north in the interior to southern Arkansas and extreme southeastern Oklahoma.
States/Provinces: AL, AR, FL, GA, LA, MS, NC, OK, SC, TX, VA
|US Forest Service Ecoregions (2007)|
Southeastern Mixed Forest Province
Confident or certain
Southern Mississippi Alluvial Plain Section
Confident or certain
Confidence Level: Moderate
Confidence Level Comments:
Magnolia virginiana - Persea palustris - Pinus serotina Swamp Macrogroup
Synonomy: > Atlantic White-Cedar 97 (Eyre 1980)
> Atlantic white cedar swamp forest (Christensen 2000)
= Bay Swamp (Ewel 1990b)
> Bay forests, bayheads, and baygalls (Christensen 2000)
= Hardwood flats and warm temperate peatlands of the coastal plain (Brinson and Malvarez 2002)
>< Pocosins (Christensen 2000)
> Pond Pine 98 (Eyre 1980)
> Slash Pine - Hardwood 85 (Eyre 1980)
> Sweetbay - Swamp Tupelo - Redbay 104 (Eyre 1980)
> Wetland Baygall Shrub Thicket (Marks and Harcombe 1981)
Concept Author(s): K.C. Ewel (1990b)
Author of Description: C.W. Nordman, R.K. Peet and M. Pyne
Version Date: 15Oct2014
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