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The Atlantic and Gulf Coastal Plain Province is a coastal plain floristic province within the North American Atlantic Region, a floristic region within the Holarctic Kingdom. It lies to the east and south of the Appalachian Province, from southern Nova Scotia to northeastern Mexico. The narrow coastal strip in New England widens in New Jersey to a broad plain through the Delmarva Peninsula, Virginia, the Carolinas, southern Georgia, and much of Florida. Along the Mississippi Embayment, the province stretches up to the confluence of the Ohio and Mississippi rivers in Cairo, Illinois.[1] The province can be further subdivided into the Atlantic coastal plain and Gulf coastal plain.[2]

Although no floristic treatment has been attempted on the province, it was designated the 36th biodiversity hotspot in 2016 due to having more than 1,500 endemic plant species combined with 70% habitat loss.[3]

Definition

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The North American Coastal Plain can be defined as the Geological Coastal Plain that is formed of soft rock layers that have been deposited over the past 100 million years at low relief.[4] This region stretches along the Atlantic Coast, east of the Piedmont from Massachusetts to Florida and along the Gulf Coast to east Texas and as further south into northeastern Mexico.[5][6] Taxa within southern Texas and northeastern Mexico are included within the Sonoran Floristic Province, and taxa within south Florida are part of the West Indian Floristic Province. Therefore, these regions are excluded from the geographic definition of the Atlantic and Gulf Coastal Plain Province.[6]

Ecosystems and Plant Communities

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Pine Communities

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Xeric Sandhill Pine Forests

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Sandhills consist of coarse, well-drained, and nutrient-limited sands, and the plant community is thus dry-adapted and often sparse[7]. Longleaf pine (Pinus palustris) forms a sparse canopy and may be co-dominant with slash pine (Pinus elliotti). Oaks such as turkey oak (Quercus laevis), sand post oak (Q. margaretta), and bluejack oak (Q. incana) occur in the understory. Persimmon (Diospyros virginiana) also occurs in the understory[7]. Wiregrass (Aristida, particularly A. stricta) is characteristic of the herbaceous layer. Other herbaceous plants, such as bull nettle (Cnidoscolus stimulosus), sand spikemoss (Selaginella arenicola), and the pine barren stitchwort (Minuartia caroliniana), are xerophytic and sparsely distributed[7]. Stress-tolerant ericaceous shrubs are common and scattered among the wiregrass. These include dwarf huckleberry (Gaylussacia dumosa), staggerbush (Lyonia mariana) and some Vaccinium species[7]. With a dominance of wiregrass on the surface, which is very flammable and fire-adapted, low-intensity surface fires (every 3-10 years) are frequent and maintain the plant community[7].

Xeric Pine Scrub

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Scrub communities also exist on well-drained, nutrient-limited soils, namely in Florida. However, fire is less frequent (30-60 year return interval) allowing "scrubby", slow-growing and schlerophyllous shrubs to accumulate, resulting in intense, crown fires that often kill the pines and aboveground growth of the shrubs[8][7]. Thus, sand pine (Pinus clausa) is the dominant canopy tree, as it is adapted to crown fires, which release seeds from its serotinous cones[7], resulting in largely even-aged stands[9]. Saw palmetto (Serenoa repens) and scrub palmetto (Sabal etonia) are common in the understory along with various scrub live oaks, such as sand live oak (Quercus geminata), myrtle oak (Q. myrtifolia), and southern live oak (Q. virginiana). Scrub rosemary, Ceratiola ericoides, is an allelopathic, ericaceous shrub that forms a habitat with many gaps caused by its allelopathy, which prevents growth of surrounding plants. A number of endemic perennial herbs have adapted and specialized to growing in these gaps, including Eryngium cuneifolium, Hypericum cumulicola, and Polygonella basiramia[10]. Common (though not typically abundant) herbaceous species include the scrub rush (Rhynchospora megalocarpa), wiregrass, Florida bluestem (Andropogon floridanus)[7]. There is a diversity of other herbaceous plants and shrubs that are adapted to this habitat, including silkbay (Persea humilis), gopher apple (Licania michauxii), rusty staggerbush (Lyonia ferruginea), and scrub balm (Dicerandra frutescens)[11].

Mesic Flatwoods

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"Flatwoods" is a general term and is less classifiable, but is used to describe forests with a pine canopy on poorly drained soils that allow a well-developed woody understory.[7] These soils may be moist or dry depending on the season[7]. Longleaf pine is dominant, though may be co-dominant with slash pine[7][12]. A variety of woody taxa and saw palmetto and wiregrass are abundant in the understory[12]. Understory vegetation can vary depending on geographic location, soil moisture, and fire frequency[12]. Slash pine is more common in wetter sites, whereas drier flatwoods are dominated by longleaf pine in the overstory[12], and dwarf live oak (Quercus minima) and other oaks are more common in the understory[7]. Flatwood communities with more frequent fire have greater herb cover[7]. Common woody shrub species in flatwoods include gallberry (Ilex glabra), wax myrtle (Myrica cerifera), dwarf huckleberry, pawpaw (Asimina reticulata), and fetterbush (Lyonia lucida)[7][12][13]. Common herbaceous species include chain fern (Woodwardia virginica), bracken fern (Pteridium aquilinus), Andropogon species, and a diversity of composite species[7][12][13].

Mesic Savannas

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Soils are more fine-textured and seasonally saturated in pine savannas[12]. Several pine species grow sparsely, producing the canopy. These include longleaf pine, slash pine, and pond pine (Pinus serotina)[12]. Low-intensity, frequent summer fires induce savanna communities where the understory is dominated by herbaceous species. If fire frequency decreases, shrubs will invade the understory, potentially succeeding into flatwoods[7]. Thus in savannas, there is a diversity of graminoids - such as wireleaf dropseed (Sporobolus teretofolius), toothache grass (Ctenium aromaticum), and striped beakrush (Rhynchospora plumosa); orchids - such as grassleaf ladies' tresses (Spiranthes praecox) and grass pink (Calopogon tuberosus); and insectivorous plants, including pitcher plants (Sarracenia), bladderworts (Utricularia), sundew (Drosera), and the Venus flytrap (Dionaea muscipula)[7][14]. Other typical herbaceous species of mesic pine savannas include pipewort (Eriocaulon decangulare), bulltongue arrowhead (Sagitaria lancifolia), false foxgloves (Agalinis spp.) yellow-eyed grass (Xyris spp.), and milkworts (Polygala spp.)[14].

Hardwood Forests

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Hardwood forests exist in a gradient of soil types and moisture availability. Various fire-dependent communities of the Coastal Plain will succeed to hardwood forests in the absence of fire[7]. When fire is excluded (whether from natural breaks or human intervention), sandhill and scrub communities, which exist on sandy, well-drained soils, succeed into xeric hammocks that may retain many of the same species[15]. Evergreen live oaks, such as sand live oak, turkey oak, sand post oak, are able to grow upward and dominate the canopy. Pines (eg. slash pine, longleaf pine, sand pine) may still form an emergent canopy[7][15]. Common understory plants include saw palmetto, myrtle oak, wild olive (Cartrema americanus), southern prickly ash (Zanthoxylum clava-herculis), yaupon holly (Ilex vomitoria), rusty staggerbush, pignut hickory (Carya glabra), American beautyberry (Callicarpa americana), rosette grasses (Dichanthelium spp.), and wiregrass[11][15]. Spanish moss (Tillandsia usneoides) and ballmoss (Tillandsia recurvata) are common epiphytes, and common vines include muscadine (Vitis rotundifolia) and greenbriar (Smilax spp.)[15]. Upland hardwood forests are more typical of eastern deciduous forests and occur on mesic, poorly-drained, soils that are high in organic material[7][15]. They occur in areas protected from fire, such as rolling hills or slopes above floodplains, and have a closed canopy dominated by deciduous trees[15]. Canopy trees include Florida maple (Acer floridanum), sweetgum (Liquidambar stryaciflua), pignut hickory, southern hackberry (Celtis occidentalis), American beech (Fagus grandifolia), southern magnolia (Magnolia grandiflora), and southern live oak. Other tree species that occur in the midstory include red bay (Persea borbonia), American hornbeam (Carpinus caroliniana), eastern hophornbeam (Ostrya virginiana), flowering dogwood (Cornus florida), basswood (Tilia americana), black cherry (Prunus serotina), gum bully (Sideroxylon lanuginosum), and devil's walkingstick (Aralia spinosa)[15]. Common shade-tolerant herbaceous species include Trillium spp., ebony spleenwort (Asplenium platyneuron), violets (Viola spp.), longleaf woodoats (Chasmanthium sessiliflorum), and Virginia creeper (Parthenocissus quinquefolia)[15]. Tree recruitment from saplings is largely through gap succession and replacement[7]. Hardwood forests along slopes in the Apalachicola River drainage have a high diversity of trees and shrubs, including taxa with affinities to the cool and moist slopes of the Southern Appalachian Mountains and Piedmont, such as mountain laurel (Kalmia latifolia) and heartleaf (Hexastylis arifolia), and very rare, endemic taxa such as Florida yew (Taxus floridana) and Florida torreya (Torreya taxifolia)[15].

Wetlands

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Wetlands cover a large portion of the land surface on the Coastal Plain and broadly describe many types of areas that undergo some inundation regime. Freshwater wetlands may be formed from rivers (Alluvial wetlands) or other means (Nonalluvial wetlands). In permanently inundated areas along rivers (or in oxbow lakes), submerged aquatics such as .. occur, Swamp forests occur along rivers or in depressions in floodplains where soils are typically saturated. Bald cypress is dominant tree species, though pond cypress may be more abundant in sandier areas. Species of tupelo are common trees as well. There are a variety of other canopy trees that may be present, particularly in swamp forests with less frequent inundation. These include laurel oak (Quercus laurifolia), red maple (Acer rubrum), American elm, water hickory (Carya aquatica), and sweetgum.

History

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Evolutionary History

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The earliest fossils of terrestrial plants in the Coastal Plain date to the Cretaceous and include a diversity of flora including pine, birch, fir, and oak. Climate in this region was mostly warm and humid during the Paleogene (66 - 23 million years ago). While much of the Coastal Plain was inundated, tropical forests occurred along the Gulf Coast in the Paleocene (66 - 59 mya). Many exposed parts of the Coastal Plain were seasonally dry during the Eocene, and fire adapted taxa, such as Sabal, Quercus, and Ephedra were present. Global cooling occurred during the Oligocene, many tropical species were replaced with temperate species, and more of the Coastal Plain was exposed as sea level dropped. During the Miocene, subtropical flora existed in Florida and other southern coastal areas. Savannas were also common in Florida, and pine woodlands and hardwood forests were widespread in other parts of the Coastal Plains. The climate became more seasonal with cool and dry periods, and C4 grasses along with other fire-adapted were widespread by the late Miocene.

Pre-European Settlement

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Human settlement in the Coastal Plain dates back to ____, though the earliest evidence for human-induced landscape fires date to ____. There is still considerable debate regarding the relative role of human-induced compared to lightning-induced fire regimes in shaping modern ecosystems of the Coastal Plains.

Post-European Settlement

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Frequent burning was still induced by Seminoles and European settlers. During the 1920s, fire suppression campaigns were started to avoid loss of commercial timber. Much of the longleaf pine ecosystems were clearcut during this time.

Threats and Conservation

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Endemic Taxa

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Around 1620 taxa, about 29% of all taxa in this region, are endemic. Some notable endemics are provided below.

  • Pinus palustris
  • Pinus elliotii
  • Ceratiola
  • Gordonia

References

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  1. ^ Thorne, Robert F. (2009-07-16). "Chapter 6: Phytogeography of North America North of Mexico". Flora of North America. Vol. Volume 1: Introduction. Archived from the original on 2017-08-25. Retrieved 2017-08-24. {{cite book}}: External link in |volume= (help)
  2. ^ W. Henry McNab and Peter E. Avers (compilers) (July 1994). "Ecological Subregions of the United States (WO-WSA-5)". Retrieved 2017-08-24.
  3. ^ Noss, Reed (2016-02-18). "Announcing the World's 36th Biodiversity Hotspot: The North American Coastal Plain". Critical Ecosystem Partnership Fund. Archived from the original on 2018-02-11. Retrieved 2018-02-11.
  4. ^ Landscape Evolution in the United States. 2013. doi:10.1016/c2011-0-05551-5. ISBN 9780123977991.
  5. ^ Noss, Reed F.; Platt, William J.; Sorrie, Bruce A.; Weakley, Alan S.; Means, D. Bruce; Costanza, Jennifer; Peet, Robert K. (2015). "How global biodiversity hotspots may go unrecognized: lessons from the North American Coastal Plain". Diversity and Distributions. 21 (2): 236–244. doi:10.1111/ddi.12278. ISSN 1472-4642. S2CID 84685018.
  6. ^ a b Sorrie, Bruce A., and Alan S. Weakley. "Coastal plain vascular plant endemics: phytogeographic patterns." Castanea (2001): 50-82.
  7. ^ a b c d e f g h i j k l m n o p q r s t u Christensen, N. L. 1989. Vegetation of the southeastern coastal plain. In: North American Terrestrial Vegetation. Eds. M. G. Barbour and W. D. Billings.  Cambridge University Press.
  8. ^ Schmalzer, Paul A. "Growth and recovery of oak-saw palmetto scrub through ten years after fire." Natural Areas Journal 23.1 (2003): 5-13.
  9. ^ Myers, Ronald L. "Fire and the dynamic relationship between Florida sandhill and sand pine scrub vegetation." Bulletin of the Torrey Botanical Club (1985): 241-252.
  10. ^ Hunter, M. E.; Menges, E. S. (2002-07-01). "Allelopathic effects and root distribution of Ceratiola ericoides (Empetraceae) on seven rosemary scrub species". American Journal of Botany. 89 (7): 1113–1118. doi:10.3732/ajb.89.7.1113. ISSN 0002-9122. PMID 21665711.
  11. ^ a b Duever, Linda. 1983 (August). Florida's Natural Communities: Inland Sand Ridges. The Palmetto 3, #3:1-3, 10.
  12. ^ a b c d e f g h Peet, R.K. (2006) Ecological classification of longleaf pine woodlands. The longleaf pine ecosystem: ecology, silviculture and restoration (ed. by S. Jose, E. Jokela and D. Miller), pp. 51–93. Springer. New York.
  13. ^ a b Duever, Linda. 1984-85 (Winter). Florida's Natural Communities: Flatwoods. The Palmetto 4, #4:6.
  14. ^ a b Duever, Linda. 1984-85 (Winter). Florida's Natural Communities: Flatwoods. The Palmetto 4, #4:6.
  15. ^ a b c d e f g h i Florida Natural Areas Inventory (FNAI). 2010. Guide to the natural communities of Florida: 2010 edition. Florida Natural Areas Inventory, Tallahassee, FL.
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