FLORA AND VEGETATION
A full list of all plants collected on the island by me as well as by W. R. Anderson and R. L. Wilbur is appended. The specimens are deposited in the herbarium of Duke University.
For vascular plants, the nomenclature of Guide to the Vascular Flora of the Carolinas (Radford et al. 1964) is followed except where another authority is cited. The nomenclature for mosses, liverworts, and lichens is based on A List of the Mosses of North America (Crum et al. 1965), List of Hepaticae Found in the United States, Canada, and Arctic America (Evans 1940), and A Third Checklist of the Lichens of the Continental United States and Canada (Hale and Culberson 1966), respectively.
The scientific-common name index was compiled from Gray's Manual of Botany (Fernald 1950), the author's list appended, and The Lichen Book (Nearing 1962).
Due to diverse physiographic features, 281 species and varieties of vascular plants belonging to 83 families, 14 species of mosses, 2 species of liverworts, and 21 species of lichens (foliose and fruticose) have been collected on the island. The number of vascular plants is relatively large as compared with other areas on the Outer Banks; Kearney (1900) recognized 135 species on Ocracoke, N.C., and Harshberger (1900) observed 228 species in the New Jersey strand flora. Small and Martin (1958) reported 267 species of vascular plants representing 63 families at Island Beach State Park, N.J.a peninsula of almost the same size (2300 acres) as Shackleford Bank (2280 acres).
Lewis (1917) listed 241 species of vascular plants in his paper. In the present checklist there are 87 species of vascular plants not found or recognized by Lewis, while 47 species in Lewis' list were not found in this study. By applying Jaccard's (1912) formula for the community coefficient
w is the number of species on both checklists, a is the number of species in the old checklist, and b is the number of species in the present checklist, a coefficient of 74.3 is obtained. In other words, there is about 74% similarity between these two checklists. Some species listed in Lewis' paper appear to be misidentified, and the present checklist is based on a more thorough opportunity for collecting specimens. Nevertheless, the coefficient of 74 may indicate that the flora of the island has undergone some change in the past 50 years under relatively unstable environmental conditions. Consequently, the appended checklist will serve as a background against which future changes may be viewed.
The base map was obtained by tracing the outline of a series of serial photographs of 1:7920 scale taken in 1964. Though major vegetation types could be recognized from the aerial photographs, the validity of lines from tracing and various plant communities were checked and defined by personal reconnaissance in the field as well as color aerial photographs taken by the author.
Classification of Plant Communities
Detailed classifications of strand vegetation on the Outer Banks of North Carolina have been proposed by Kearney (1900) on Ocracoke, by Lewis (1917) on Shackleford Bank, by Rondthaler (1952) on Ocracoke, and by Brown (1959) on the Outer Banks in general. Their systems of classification are listed as follows in comparison with a new system that I proposed.
I. Sand strand vegetation
I. Sand strand vegetation
I. Sand strand vegetation
I. Sea beach
I. Grassland vegetation
Description of plant communities
Principal plant communities in each type of vegetation are named according to their dominant species. The number after each community indicates its locations on the vegetation map (Fig. 3). In fact, the plant communities which belong to the same vegetation type are alike in physiognomy, species composition, and habitats. The only difference among them is a shifting in importance of the dominant species.
I. Grassland vegetation
Outer beach: Spurge (Euphorbia maculata) and spike grass (Uniola laxa) community (1). It is typically a flat and barren sandy waste above the mean high-tide line (Pl. I-1), about 30 m wide, covered with an abundance of large shell fragments deposited by occasional floods during winter storms. Very little vegetation occurs on the drifting sands except for a few small clumps of sea oats which build up incipient dunelets, and sparsely scattered individuals of seaside spurge (Euphorbia polygonifolia). The latter is, in fact, the species occurring nearest to the sea. It may be aided in its adaptation to salt spray by its prostrate growth form. Other species found here are sea rocket (Cakile edentula), common saltwort (Salsola kali), and seabeach amaranth (Amaranthus pumilus). As a whole, the vegetation of the outer beach is exceedingly sparse.
Inner beach: Cordgrass (Spartina), spike grass, and water pennywort (Hydrocotyle) community (2). Between the mean high-tide line and the grassy dunes or maritime forest on the sound side is a narrow strip of inner beach which is also largely barren (Pl. III-22). Here, the more common species are saltmeadow cordgrass (Spartina patens), sea oats, silver-leaf croton (Croton punctatus), and seaside pennywort (Hydrocotyle bonariensis). Other species frequently found are seabeach evening primrose (Oenothera humifusa), sandspur (Cenchrus tribuloides), ground cherry (Physalis maritima), horseweed (Conyza canadensis), and smartweed (Polygonum glaucum). Common saltwort grows occasionally in abundance along the upper edge of the inner beach. Very close to the water is sea beach orach (Atriplex arenaria), a species which withstands temporary submergence and thus is one of the strand's most halophytic species.
Grassy dunes: Spike grass, beardgrass (Andropogon), and croton (Croton glandulosus) community (5). The dune environment presents one of the most unstable plant habitats. Sea oats, a successful dune builder and stabilizer, occupies more than 90% of the vegetated dune area (Pl. I-7). Secondary components are dune bluestem (Andropogon littoralis), silver-leaf croton, and seabeach evening primrose. Other herbs occurring on the dunes include horseweed, sandspur, sandgrass (Triplasis purpurea), seaside spurge, seaside pennywort, and, on lower gentle dunes, saltmeadow cordgrass and ground cherry. A single shrubby species, seashore elder (Iva imbricata), is rarely found on the dunes of Shackleford Bank, in contrast to its abundance on Bogue Banks or Bear Island to the west; nor has beach grass (Ammophila breviligulata) been found by the author though the species is widely planted at Fort Macon just across Beaufort Inlet. Several vines successively colonize the rear dunes: Virginia creeper (Parthenocissus quinquefolia), poison ivy (Rhus radicans), China brier (Smilax bona-nox), wild bean (Strophostyles helvola), pepper vine (Ampelopsis arborea), and muscadine grape (Vitis rotundifolia). On the sand wall, cudweed (Gnaphalium purpureum), sea burdock (Xanthium echinatam), goldenrod (Solidago sempervirens), and red mulberry (Morus rubra) are to be found.
Spike grass, marsh elder (Iva), and saltwort (Salsola) community (3). This community represents a stage in the development of the grassy dunes on loose sandy wastes. The dominants are sea oats, seashore elder, and goosefoot saltwort. Other species that occur frequently are sea rocket, seaside spurge, smartweed, seabeach amaranth, seaside pennywort, saltmeadow cordgrass, purple sand grass, and wild bean.
Croton, common thistle (Cirsium), and spike grass community (22). This community develops on dunes made up largely of shell fragments, a highly alkaline substratum. Silver-leaf croton is the dominant species and yellow thistle (Cirsium horridulum) grows in abundance, Beside the much-repressed sea oats, there are seaside pennywort, saltmeadow cordgrass, palmetto (Sabal minor), and seaside spurge.
Grassy sand flat: Cordgrass, rush (Juncus), and beardgrass community (19). This community covers the greatest area on the eastern part of the island (Pl. III-23, 24). It occurs also between salt marshes on the sound side and low dunes on the ocean side. The elevation of the gentle flat is generally no more than a meter above the high-tide level. Here and there are dark-green clumps of rush which usually occupy the moist sites on the meadow, often associated with small patches of fresh to brackish marshes. Characteristic species are saltmeadow cordgrass, rush, and hair grass (Muhlenbergia capillaris), together with various grasses, sedges, and rushes. Other abundant species are broom sedge (Andropogon virginicus), Fimbristylis castanea, chairmaker's rush (Scirpus americanus), foxtail grass (Setaria geniculata), sea pink (Sabatia stellaris), cyperus (Cyperus), and whitetop sedge (Dichromena colorata). Seaside pennywort and finger grass (Chloris petraea) are dominant on slightly elevated dry sites. Secondary species are blanket flower (Gaillardia pulchella), ground cherry, sandspur, purple sandgrass, nodding ladies' tresses (Spironthes vernalis), and horseweed. Scattered small, woody plants include shrubby marsh elder (Iva frutescens), sea myrtle (Baccharis halimifolia), wax myrtle (Myrica cerifera), and red cedar.
Cordgrass, Fimbristylis, and Muhly (Muhlenbergia) community (23). Basically, this community is not very different from the community mentioned above except that the dominants are saltmeadow cordgrass, Fimbristylis castanea, and hair grass.
Cordgrass, rush, and beardgrass community (7). This community develops in interdunal slacks habitats where the water table comes close to the ground surface. Dominant species are saltmeadow cordgrass, rush (Juncus coriaceus), and broom sedge. Secondary species are chairmaker's rush, rush, seaside pennywort, Fimbristylis castanea, sea pink, and foxtail grass. On areas with a frequent wet surface, hydrophilic species such as capeweed (Lippia nodiflora), water pimpernel (Samolus parvuflorus), water hyssop (Bacopa monnieri), whitetop sedge, and climbing hempweed (Mikania scandens) prevail.
II. Woodland vegetation
Forest: Oak (Quercus), juniper (Juniperus), and holly (Ilex) community (10). Live oak, red cedar, and American holly (Ilex opaca) are the three most important tree species of maritime forest (Pl. III-17, 18). As represented on Shackleford Bank, the forest is about 5-10m high. Well-developed live oak trees may reach a diameter of 66 cm. The abundant woody vines and low shrubs often make it difficult to force a passage through the luxuriant forest. Common species of trees, in addition to the three important ones mentioned above, are willow oak (Q. phellos), loblolly pine (Pinus taeda), sweet bay (Magnolia virginiana), red bay (Persea borbonia), flowering dogwood (Cornus florida), wild olive (Osmanthus americanus), wax myrtle, and Hercules' club (Zanthoxylum clava-herculis). Species of shrubs or smaller trees making up an understory include yaupon (Ilex vomitoria), ironwood (Carpinus caroliniana), beauty berry (Callicarpa americana), red mulberry, and dwarf sumac (Rhus copallina). Palmetto is occasionally present inside the forest but more abundant at the edge of maritime forest behind the rear dunes. The number of herbaceous species is small and the vegetational ground cover is scanty. The principal herbaceous species are spike grass, needle grass (Stipa avenacea), partridge berry (Mitchella repens), Spanish needles (Bidens bipinnata), elephant's foot (Elephantopus nudatus), pepper grass (Lepidium virginicum), bullnettle (Cnidoscolus stimulosus), and panic grass (Panicum). Epiphytic species, mostly on live oak, are Spanish moss (Tillandsia usneoides) (Pl. III-17), mistletoe (Phoradendron serotinum), and resurrection fern (Polypodium polypodiodes). Lichens are abundant on tree trunks and branches, especially on live oak where species of shield lichen (Parmelia), blister lichen (Physcia), twig lichen (Ramalina), beard lichen (Usnea), and shore lichen (Teloschistes) flourish. However, the most conspicuous lichen is wedding ring (Lopadium leucoxanthum), a crustose which grows best on American holly and occasionally on yaupon. For this reason, one can recognize American holly at a distance by a bright red patch on the bark. At High Hill, a large quantity of several sod lichen (Cladonia) species covers the ground under the forest. Finally, there are numerous woody vines climbing into the canopy, such as greenbrier (Smilax), muscadine grape, Virginia creeper, pepper vine, rattan vine (Berchemia scandens), and poison ivy.
Thicket: a. Dry thicketHolly, juniper, and oak community (11). This community is characterized by small shrubs usually no more than 5 m high which grow close together and are tangled with various woody vines. Behind dunes, the thicket is composed chiefly of yaupon which in some areas forms an almost pure stand. Four other important components are red cedar, live oak, Hercules' club, and beauty berry. Associated vines are summer grape (Vitis aestivalis), muscadine grape, Virginia creeper, china brier, catbrier (Smilax auriculata), pepper vine, and poison ivy. Portions of the dry thicket are not readily penetrable due to the dense growth of shrubs and vines. However, pure stands of dwarf yaupon usually have ample bare ground sparsely beset with such herbaceous species as frostweed (Helianthemum georgianum), purple sand grass, finger grass, and prickly pear (Opunita humifusa).
b. Wet thicketWax myrtle, juniper, and oak community (9). The physiognomy of this community is similar to that of the dry thicket but it occupies the wet sites. The dominants are wax myrtle, red cedar, live oak, and gallberry (Ilex glabra). Secondary species are beauty berry, shrubby marsh elder, red mulberry, and, occasionally, dogwood (Cornus stricta). Woody vines tangled on top of wet thicket (Pl. III-21) are china brier, bamboo (Smilax laurifolia), muscadine grape, Virginia creeper, and rattan vine. Many herbaceous species typical of marshes find their niches on the wet ground here.
Scrub flat: Wax myrtle, juniper, and cordgrass community (6). This community is basically a grassy sand flat, but with a large number of saplings or small shrubs of red cedar and wax myrtle. From the trend of colonization by woody species, scrub flats may be regarded as a successional stage leading to the maritime forest. Other shrubs which are rather abundant are shrubby marsh elder and sea myrtle.
III. Marshland vegetation
Freshwater marsh: a. Dune marshFimbristylis, water pennywort, and fogfruit (Lippia) community (24). This community is found in small depressions formed by "blow-outs" among grassy dunes (Pl. IV-29). Basically, it is a poorly developed fresh marsh. Its water is derived wholly from rainfall. These marshes may become small fresh-water ponds (Pl. II-9, 10) after a heavy rain, particularly in the spring, or dry up following a long drought. Consequently, the flora is far poorer than that of well-developed fresh-water marshes. Major species are sedges and rushes such as Fimbristylis castanea, chairmaker's rush, rush (Juncus megacephalus), and whitetop sedge. Creeping on the ground, in large numbers, are seaside pennywort, capeweed, smartweed. and water hyssop. Nodding ladies'-tresses and saltmeadow cordgrass are occasionally present.
b. Freshwater marsh: Wherever the water table reaches the soil surface within the maritime forest or between wet thickets, and at the same time is isolated from the ocean, a fresh-water marsh possessing the richest flora of any of the bank's communities is formed. The fresh-water marsh is usually covered by a thin layer of water or is at least saturated and, thus, is difficult to traverse. In the spring and summer, it is often flooded and turns into a shallow swamp. Only late in the fall, when dry weather prevails, can one walk through it without sinking into the mud. Since numerous ticks thrive there in the summer and an appalling number of mosquitoes prosper in it from spring until late fall, the fresh-water marsh is the least comfortable place in which to work.
Cattail-flag (Typha), rush, and twig-rush (Cladium) community (8). In addition to the pure patches of common cattail (Typha latifolia), saw grass (Cladium jamaicense) (Pl. IV-27) and rush, other common species are Fimbristylis castanea, broom sedge, rush, foxtail grass, whitetop sedge, morning glory (Ipomoea sagittata), and seaside pennywort.
Rush, cattail-flag, and mallow (Kosteletzkya) community (13), This is an intraforest fresh-water marsh with the richest flora of all marsh communities. Dominants are rush, common cattail, and seashore mallow (Kosteletzkya virginica). Secondary species are saw grass, rush, chairmaker's rush, cyperus, paspalum (Paspalum floridanum), spike rush (Eleocharis albida), and whitetop sedge. Other abundant species are false nettle (Boehmeria cylindrica), marsh fleabane (Pluchea), false loosestrife (Ludwigia), water hemlock (Cicuta maculata) knotweed (Polygonum), morning glory, climbing hempweed, nodding ladies'-tresses, fleabane (Erogeron quercifolius), duck potato (Sagittaria latifolia), water pimpernel, ebony spleenwort (Aspienium platyneuron), and bracken fern (Pteridium aquilinum). Creeping on the ground are capeweed, seaside pennywort, pennywort (Centella asiatica), and water hyssop.
c. Brackish marsh: Wherever a sandy beach or a low dune develops obstructing the passage of water in a creek marsh, a brackish marsh is formed. It is gradually transformed to a brackish or even to a fresh-water marsh, depending upon the thoroughness of leaching. Consequently, both salt marsh and fresh-water marsh species may grow in such a brackish habitat with their proportions depending upon the salinity of the substratum.
Rush, groundsel tree (Baccharis), and beardgrass community (14). Dominants are rush, sea myrtle, and broom sedge. Secondary species include goldenrod and small shrubs of red cedar and wax myrtle.
Marsh elder, Fimbristylis, and water pennywort community (16). Dominants are shrubby marsh elder, Fimbristylis castanea, and seaside pennywort. Secondary species are rush, saltmeadow cordgrass, foxtail grass, broom sedge, and wax myrtle.
Cordgrass, rush, and water pennywort community (17). Dominants are saltmeadow cordgrass, rush, and seaside pennywort. Less abundant herbaceous species include Fimbristylis castanea, broom sedge, foxtail grass, and cyperus. Woody species include wax myrtle, sea myrtle, and red cedar.
Creek marsh: Along the sound side of the western part of the island, there are several creek marshes surrounded by higher ground, excepting the narrow creek which permits the twice daily passage of tidal water. Usually, several vegetational zones are distinguished by the distance from the entrance of a tidal stream. Each zone is dominated by one or two species. A typical situation is a cordgrass (Spartina alterniflora, S. distichlis, S. spicata) zone near the entrance of tidal creek (Pl. IV-30), a rush zone, and a common cattail zone, as the water changes from salty to brackish to nearly fresh.
Rush, twig rush, and cattail-flag community (12). Dominants include rush, saw grass, and common cattail, with each species occupying a distinctive zone. Other species frequently observed at the periphery are morning glory, climbing hempweed, seashore mallow, and Fimbristylis castanea.
Rush, cordgrass, and cattail-flag community (15). This subdivision is similar to the community mentioned above, except that the dominants are rush, saltwater cordgrass (Spartina alterniflora), and common cattail.
Rush, cordgrass, and spike grass community (18). This is the typical creek marsh mentioned earlier. Dominants are rush, saltwater cordgrass, salt grass (Distichlis spicata) and common cattail. Quite a few halophytic species occur at the entrance of the tidal creek, such as perennial saltwort (Salicornia virginica), dwarf saltwort (Salicornia bigelovii), sea lavender (Limonium carolinianum) and sea ox-eye (Borrichia frutescens). Other species observed at the periphery are Fimbristylis castanea, seaside pennywort, saltmeadow cordgrass. and silver-leaf croton.
Salt marsh: Cordgrass, rush, and glasswort (Salicornia) community (20). Spreading along the sound side of the eastern half of the island is a well-developed salt marsh (Pl. IV-29). It can be further subdivided into two categories: a low salt marsh and a high salt marsh. The low salt marsh is inundated daily by tidal water and its silty substratum is permanently moist, whereas the high salt marsh is only occasionally inundated by the highest tides and generally is less salty. Saltwater cordgrass, which can withstand temporary complete submergence, is the preponderant species of the low salt marsh. Associated with it, rather abundantly, are dwarf and perennial glasswort (Salicornia bigelovii, S. virginica). Less important members are salt grass and sea lavender. In the high salt marsh, saltmeadow cordgrass and rush are dominants. Other species found in this community are Fimbristylis castanea, sea ox-eye, and sea beach orach. Small shrubs include sea myrtle, shrubby marsh elder, and sometimes wax myrtle growing at the higher fringe of the salt marsh.
Cordgrass, spike grass, and Fimbristylis community (4). This is the only salt marsh community at the western half of the island and its area is less than 1 acre (0.4 ha). The community is heavily grazed by livestock, especially by cows and horses, Dominants are saltwater cordgrass, salt grass, and Fimbristylis castanea. Secondary species are sea ox-eye, perennial saltwort, and sea beach orach.
Cordgrass community (21). This salt marsh community is separated from the island proper and consists of pure stands of saltwater cordgrass.
In the remnant forest, most of the live oak trees are probably less than 70 years old, Therefore, some of them might have been developed from seeds set by a few surviving old trees after the devastating hurricane of 1899. However, pure patches of live oak trees about the same size are often found in the forest. It is conceivable that they might have developed by vegetative propagation from an old tree half-buried by dune sands.
Due to the mild maritime climate, herbaceous plants can colonize the barren ground rapidly. Lewis (1917) described the eastern half of Shackleford Bank as follows: "From Wade's Shore to Cape Lookout, both forest and swamp have disappeared completely save for one or two small groves of live oak, which have been able to resist the advancing sand. Elsewhere this portion of the island is a sandy waste, with little or no vegetation,..." Today, a well-developed meadow covers that once sandy waste. Furthermore, young seedlings and small shrubs of red cedar and wax myrtle are found in abundance in some sections of the grassy flat (Pl. III-21). The recolonization of the newly formed sandy surface can also be seen at the western end of the island (Pl. I-2). Also, in situations where the sand wall of the rear dunes have been stabilized by herbaceous plants, a number of woody seedlings are established.
The speed of succession is relatively fast at the moist sites but rather slow on the dry sand of the dunes. Under favorable conditions, individuals of red cedar and wax myrtle will be the pioneer trees to appear on a grassy flat or a moist depression. Their important roles lie in the gradual improvement of soil fertility as well as soil physical properties by the accumulation of organic materials. On the other hand, yaupon is a successional species on dry sites, especially behind the sand dunes.
Three serial pathways leading to a maritime forest can be recognized (Fig. 4). On a protected sandy waste, herbaceous species need only a couple of years to colonize such barren ground. Afterwards, shrubby species and tree seedlings may develop on the grassy flat, providing that a seed source is available, A scrub flat is thus formed and will eventually progress to a maritime forest. On an unprotected sand barren, the interaction of prevailing onshore wind and the vegetative propagation of sea oats creates numerous incipient dunelets. As these dunelets grow bigger and connect to each other, a series of grassy dunes is produced. Because of the lack of available water, grassy dunes develop very slowly through a dry thicket stage and finally into a maritime forest. The last pathway may begin with an enclosed creek marsh, which, after continuous leaching by rainwater, is converted unto a fresh-water or slightly brackish marsh. The marsh then develops through a wet thicket to a maritime forest.
Environmental factors such as shifting sand, salt spray, and topography may hold one type of vegetation in a comparatively stable condition for a long while. Succession does not follow a definite pathway, for many environmental factors may change or even reverse its direction completely. In short, the topography and the vegetation are constantly modified by all environmental factors, and vice versa. Therefore, the ecosystems on the island are not static, but dynamic and subject to frequent changes. However, plant succession occurs in a more restricted way on the island in comparison with the old field succession of Piedmont, N.C.
Table 1 shows the land surface occupied by major vegetation types in terms of percentage, acres, and hectares. The area of each vegetation type was determined with a planimeter from the vegetation map. Grassy sand flat, grassy dunes, and bare sand account for 82% of the total area while less than 4% of the island is currently covered by forest. However, as indicated in the foregoing descriptions of plant communities, the vegetation on the island is rather diversified and certainly represents one of the few rich remnants of maritime vegetation on the North Carolina coast. The diversified habitats and complex vegetational patterns resulting from the varied physiographic features support a surprisingly rich flora on such a small island. The second portion of this study will investigate some aspects of these complex environmental and topographic patterns.
Last Updated: 7-Jul-2005