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Biological Components of Dunes and Slacks
Dune-and-slack plants Rare and endangered plants Strandline community Dune-and-slack communities Palustrine wetlands Non-vascular plants Dune-and-slack animals Rare and endangered animals Exotic species References	Dune slack environments on Bear Island, North Carolina.  Wax myrtle shrubs dominate the moist swales within the dune systems.

Dune-and-Slack Plants

The defining influences near the coast--wind, sand and salt water--establish contrasting environments expressed as a mosaic of distinct and easily recognized plant and animal communities.  Distinctive groupings of species adapted to coastal environments inhabit the dunes, slacks, maritime forests, and tidal marshes.  Description of the herbaceous dune-and-slack communities is emphasized in this chapter.

Plant Families and Life Forms

The number of plant species adapted to coastal dune-and-slack environments is low (Moreno-Casasola 1988).  Ruderal (weedy) species typically make up a significant portion of the flora of barrier beaches.  Martin (1959) found more than 267 species of vascular plants on Island Beach, New Jersey; of these, more than one-third were ruderal weeds found along the road and building sites, and nearly one-half were rare, occurring in only one to a few sites.  The bulk of the vegetation was composed of about 75 common species that form various associations.  This numerical relationship between ruderal and native species appears similar throughout the Atlantic Coast.

Families represented by the greatest number of species along the Atlantic Coast are Asteraceae (asters), Cyperaceae (sedges) and Poaceae (grasses) (Stalter and Lamont 1990; Lamont and Stalter 1991).  Of the 277 vascular plant species identified at Orient Beach State Park, New York, 17 species were present in the beach community and 56 occurred in the slack community (Lamont and Stalter 1991); on Assateague Island, Virginia, 81 from a total of 443 species were present in the dune and slack community (Stalter and Lamont 1990).

Many plant families well-represented in inland floras are often poorly represented in coastal floras; Fabaceae and Rosaceae are examples.  Species of Chenopodiaceae dominate tidal marsh environments, but no families are particularly characteristic of dunes or slacks.

Both dunes and slacks have a biological spectrum rich in hemicryptophytes--plants with over-wintering buds near the soil surface.  Ranwell (1959) compared the biological spectrum of dunes and slacks at Newborough Warren, Anglesey, United Kingdom, and found that despite the presence of many therophytes (annuals) in the dunes, the life-form spectrum of dunes and slacks is similar (Table 5.1).

Coastal Plant Geography

Plant species particularly adapted to coastal environments often have broader geographical ranges than species not confined to coastal environments (Moreno-Casasola 1988).  Typically, coastal species are adapted for rapid dispersal and colonization.  Coastal conditions favor migration along the shore to a greater degree than do inland areas; thus these species can occupy geographically larger regions than inland species.  Characteristic coastal plants, such as evening primrose, Russian thistle (Salsola kali), and seaside goldenrod, occur over a wide latitudinal range along the Atlantic Coast.

Art (1976) views the Atlantic Coast flora as a continuum of species with a constant physiognomy (Fig. 5.1).  The strand, herbaceous dunes, slacks, and various wooded communities are consistently found along the coast.  Individual species increase in importance, become dominant, and then are gradually replaced in the flora along a latitudinal gradient.  For example, as northern beach pea (Lathyrus japonicus) declines in importance southward, the dominance of sea elder increases.  Similarly, cranberry (Vaccinium macrocarpon) bogs in the dunes at Cape Cod and Long Island are replaced by rush-, sedge- and cattail-dominated slacks in New Jersey and the Delmarva Peninsula.  In Georgia, similar slacks are dominated by bulrushes (Scirpus spp.), saw grass (Cladium mariscus ssp jamaicense), rushes (Juncus spp.), common frog fruit (Phyla nodiflora), and saltmeadow cordgrass.

Climate is the major limiting factor in the distribution of coastal plant species.  In contrast to Art (1976), several authors provide evidence for establishing a major division between northern and southern floras.  Small (1929) describes southern New Jersey and the Delmarva Peninsula as floristically similar and a meeting ground for southern and northern plants.  In support of this argument, bitter panic grass is near its northern limit of distribution on Assateague Island, Virginia, and Maryland (Higgins et al. 1971); Martin (1959) did not report this species at Island Beach, New Jersey.

Oosting (1954) considers North Carolina the dividing line for northern and southern components of strand communities.  Godfrey (1977) supports this view, noting a major break in temperature at Cape Hatteras, North Carolina.  The Outer Banks are warmed by the Gulf Stream; south of Cape Hatteras the mean monthly minimum temperature remains above 4/ C.  To bolster this argument, Godfrey (1977) noted that near Cape Hatteras, American beachgrass and sea oats reach their southern and northern limits of distribution, respectively.  Also, northern bayberry (Myrica pensylvanica) and beach heather reach their southern limit near Cape Hatteras.  In contrast, sea elder is found from Cape Henry, Virginia, southward. 

Lazell and Musick (1973) described what they term the intra-Capes ecological zone located between Cape Lookout and Cape Hatteras, North Carolina.  They suggest that this region is floristically depauperate and is a transition zone for several species.  For example, prickly pear cactus (Opuntia pusilla, identified as O. drummondii) is common on the dunes in the intra-Capes ecological zone but is rare north of Cape Hatteras.  Similarly, northern bayberry is absent from the zone but is common to the north.  The authors considered the intra-Cape ecological zone to be the northern limit for broomsedge (Schizachyrium scoparium ssp. Littorale, identified as Andropogon littoralis).  Lazell and Musick (1973) maintained that the distinctive flora in the zone is related to the long mean frost-free period of more than 270 days.

The highly dynamic nature of the shoreline, especially from Cape Henry, Virginia, to Cape Fear, North Carolina, may contribute to the depauperate nature of the coastal flora.  Tyndall and Levy (1978:14), in their study of Currituck Banks, North Carolina, noted that "Because of the absence of native trees which can tolerate the spray levels of the shrub zone, the replacement of a frutescent zone by an arborescent one is prevented on stable or degrading coasts.  On aggrading coasts, however, shifting salt spray levels would allow the succession of shrubs to trees.”  In the Cape Henry to Cape Fear coastal compartment, both maritime forest and pine-oak-hickory forests are scarce when compared to Cape Cod, Massachusetts, or the sea islands of Georgia.

Plant distributions reflect responses to various climatic factors, including temperature.  Under experimental conditions, the optimum daytime temperature for American beachgrass is between 21.1/ C and 26.7/ C.  The optimum daytime temperature for sea oats is greater than 26.7/ C (Seneca 1972a).  Seneca noted that the normal daily maximum temperature from June through September at the mouth of the Chesapeake Bay is 27.8/ C.  The northernmost report for sea oats is Assateague Island, Virginia, where two populations were found at the southern end of the island (Stalter and Lamont 1990).  BoulJ (1979) reported sea oats from Fisherman's Island at the northern edge of the mouth of the Chesapeake Bay. 

Godfrey discounted the role of precipitation as a factor influencing the distribution of coastal plants, but Woodhouse et al. (1968) suggested that the southern limit of American beachgrass is dependent on its combined intolerance to drought and its susceptibility to disease and insect herbivory in North Carolina.  Lucas et al. (1971) noted that American beachgrass is susceptible to the scale insect, Eriococcus carolinae, and to the fungus, Marasmiellus mesosporus.  They also hypothesized that as it approaches the natural southern limit of its distribution, American beachgrass is less tolerant of salt aerosols and flooding by salt water, especially during the warmest months.

The southern form of saltmeadow cordgrass (Spartina patens var. monogyna), most common along the southeastern Atlantic Coast, reaches its northern limit in Massachusetts.  Cabbage palm (Sabal palmetto), a southern species of palm that reaches its coastal northern limit in North Carolina, is limited in its inland distribution by the mean temperature of the coldest month (Greller 1980).  Temperature probably defines the northern coastal limit of the cabbage palm.

While American beachgrass (Fig. 5.2) is the dominant northern dunegrass, sea oats (Fig. 5.3) is dominant from Cape Henry to the State of Tobasco in Mexico (Wagner 1964).  Sea oats dominates in areas where the extreme conditions of wind-blown salt, evaporation and burial by shifting sands eliminate competing species.  Further, it can grow under conditions of low nitrogen and phosphorus; however, tillers and rhizomes of sea oats are stimulated by adding these nutrients to the soil (Woodhouse and Hanes 1966).  Sea oats cannot germinate under saline conditions where soil water is greater than about 1.0-1.5 percent NaC1 (30-45 percent of seawater strength).  This limitation restricts sea oats to the dunes; it typically does not occur on sand flats or other low areas occasionally flooded with saltwater (Woodhouse et al. 1968).

Comparisons of species lists along the Florida coast show a significant change in the flora from the north Florida beaches (Fort Clinch) to Cape Canaveral in central Florida (Apollo Beach).  The assemblage of species noted by Carlton (1977) at Fort Clinch (Table 5.2) is similar to those found as far north as Cape Hatteras.  In contrast, the floristic influence of the tropics can be seen in the species list from Apollo Beach (now part of Cape Canaveral National Seashore; Table 5.3).  Sea grape (Coccoloba uvifera), railroad vine (Ipomoea pes-caprae ssp. brasiliensis), snowberry (Chiococca alba), and bay bean (Canavalia rosea, identified as C.  maritima) are typical species with tropical affinities.  Carlton (1977) found a decreasing similarity among sites between Fort Clinch and Cape Canaveral.  South of Cape Canaveral, species similar to those in Fort Clinch were few.

Rare and Endangered Plants

Several coastal dune species are designated as rare or endangered in a state or regional context.  Rareness in these instances usually is related to the occurrence of the species at the limits of their geographical ranges.  For example, seaside broomspurge (Chamaesyce polygonifolia), considered rare in New Jersey, is abundant in the Southeast.  Seabeach sandwort (Honckenya peploides) is endangered in New Jersey (Snyder and Vivian 1981) but is more common northward.  Seaside knotweed (Polygonum glaucum), a common species in Massachusetts, is a candidate for listing as endangered or threatened in North Carolina (Sutter 1990).

Japanese sedge (Carex kobomugi) is recognized as an endangered species along the Atlantic Coast (Fairbrothers and Hough 1973).  This introduced species is reported from scattered locations between Island Beach, New Jersey (Martin 1959) and Fisherman's Island, Virginia (Boulé 1979).  Seabeach amaranth (Amaranthus pumilus), designated a federally threatened species in 1993, occurs only in the strandline, a transient environment (Fig. 5.4).  This species has been extirpated over much of its northern range.  

Strandline Community

Few species inhabit the strandline.  This habitat, besides being transient, exhibits environmental conditions that exceed the tolerance limits for most organisms, including many coastal plants and animals.  Shifting sand, wind-driven salt spray, wide temperature fluctuations, and drought-like conditions characterize the strandline environment.  Plants inhabiting the strandline exhibit life histories typical of colonizing plants:  they are generalists with short life cycles, high reproductive potentials and a wide range of environmental tolerance.  Where thick debris accumulates along strandlines, the temperature, vapor-pressure deficit and evaporation rate beneath the debris are depressed, resulting in a stable mesic microclimate (Barnes and Barnes 1954).

In a study conducted in New Hampshire and southern Maine, the organic material on the strandline consisted of the algae Ascophyllum nodosum, Fucus vesiculosus and Chrondrus crispus, eelgrass (Zostera marina), and smooth cordgrass, (Behbehani and Croker 1982).  On South Atlantic beaches, smooth cordgrass culms, eelgrass leaves, and sargassum (Sargassum sp.) thalli comprise most of the organic material on the strandline.

Along the strandline of the Atlantic shore, sea rocket, a succulent member of the mustard family (Brassicaceae), is the most characteristic species.  It and the other strandline plants trap wind-blown sand and form small embryonic dunes or dunelets.  Dunelets also may be transient, lasting only one or two seasons, especially if the shoreline is undergoing recession.  Other common species of the strandline include Russian thistle, seaside broomspurge (Chamaesyce polygonifolia) and sea purslane (Sesuvium portulacastrum).

Strandline plants typically require large amounts of nitrogen, a requirement met by bacterial decomposition of the strandline organic matter; however, as the source of nutrients is depleted, environmental conditions, and consequently, the vegetation cover change.  Soils become drier and less fertile (Ranwell 1972) and dune pioneers replace typical strandline species.  Annuals, such as Russian thistle, evening primrose and sea rocket are replaced by perennials such as sea elder, sea oats, and American beachgrass.  The sparse plant cover is replaced by a more continuous mantle as embryo dunes begin to coalesce.

Animals of the sand beach, including the strandline, were studied by Pearse et al. (1942).  They found amphipods (Orchestia sp. and Talorchestia sp.) in the strandline; however, these organisms are killed by saltwater inundation.  The amphipod, Orchestia platensis, dominates the fauna of the strandline, feeding upon the organic material (also called “wrack”) along the shore (Behbehani and Croker 1982).  Although considerable diversity was observed by Behbehani and Croker, Orchestia, the oligochaete Enchytraeus sp., and collembolans represented nearly 98 percent of the invertebrate population in the strandline.

The strandline serves as a habitat for many scavengers and predators, including beetles, flies, earwigs, collembolans, and spiders.  Ghost crabs (Ocypode quadrata) are common inhabitants of the strandline; their holes are often adjacent to dead fish and other marine animals washed onto the backshore (Fig. 5.5).  There is little seasonal variation in the animal composition of the strandline, but, as expected, the distribution of the inhabitants is highly patchy.  No animals are characteristic of the high-tide line (Pearse et al. 1942); however, several mammal species, including gray fox (Urocyon cinereoargenteus) and the raccoon (Procyon lotor), may scavenge on the beach.  

Dune-and-Slack Communities 

The floristic composition of dune-and-slack communities has been described as part of larger ecological studies throughout the coastal region.  For insight into the diversity of these habitats, three studies describing the herbaceous dune-and-slack communities in relation to the entire coastal ecosystem are summarized in this report.   Also included are other studies that describe herbaceous wetland communities within coastal dunes.

Island Beach, New Jersey

A transect of a typical northeastern barrier island, Island Beach, New Jersey, illustrates the relationships among the herbaceous communities mapped by Martin (1959), namely dunegrass, heather, marshes, and communities with extensive arborescent vegetation:  thickets, savannas, and woodlands (Fig. 5.6).  At Island Beach, salt‑tolerant species such as Russian thistle and sea rocket are most dominant in the strandline community.  Clumps of beachgrass broken away from eroded dunes dot the shoreline, especially after damaging storms.  Martin (1959) characterizes the major dunegrass community as a sparse grassland of medium height with American beachgrass and seaside goldenrod accounting for about 94 percent of the total vegetation cover.  The remaining 6 percent cover includes frequent, but not abundant, species:  sea rocket, seaside broomspurge, northern beach pea, and dusty miller.

Heather, found in topographically high and more protected sites than provided in the dunegrass community, has an open, xeric, heath-like appearance.  In this community, beach heather is the predominant plant and forms large, irregular patches.  Panic grass, pin-weed, sedge (Carex grayii), and lichens (Cladonia spp.) represent less than 10 percent of the cover in the beach heather zone.

On Island Beach, New Jersey, the secondary dune zone exhibits the highest diversity of community types.  Besides the communities found on the primary dunes, woodlands and mesic thickets also dominate the secondary dunes.  Interdune slacks may support fresh marsh, woodland, or thickets.  The freshmarsh community is highly variable in composition and may include broomsedge (Andropogon virginicus), sedges and bulrushes (Carex, Cyperus and Scirpus spp.), rushes (Juncus spp.), marsh fern (Thelypteris palustris), rose mallow (Hibiscus moscheutos), cattail (Typha latifolia), and common reed (Phragmites australis) (Fig. 5.7).

Outer Banks, North Carolina

Along the Outer Banks of North Carolina, extensive maritime grasslands occupy overwash terraces landward of a narrow, low dune system, which is punctuated by overwash passes (Godfrey and Godfrey 1976).  The scattered vegetation of the wide strandline zone is occupied by annuals:  sea rocket, seabeach amaranth, Russian thistle, seaside knotweed, and seaside broomspurge. 

Godfrey and Godfrey (1976) described a zone of maritime grasslands running down the center of the Outer Banks (Core Banks) composed of four basic habitat types:  barrier flats, dune strand, dune slacks, and mesic meadows.  All four types grade one into another.  The distribution of the barrier flats grassland community is influenced by the frequency and severity of oceanic overwash.  High, flat areas behind the berm have a characteristically open grassland appearance and are dominated by tussocks of saltmeadow cordgrass (Fig. 58).  Seaside goldenrod, seaside broomspurge, and sea rocket are also present. 

Today the dune strand consists of both low, flat dunes dominated by saltmeadow cordgrass and larger, nearly continuous dunes occupied by sea oats.  Following the stormy period of the 1950s and 1960s on the Outer Banks, dunes dominated by saltmeadow cordgrass were the most extensive type of maritime grassland on Core Banks (Godfrey and Godfrey 1976); however, since then, sea oats has increased in importance.  The characteristically hummocky dunes, formed when sea oats accumulate sand, now occupy extensive sections of once-barren flats on Core Banks.

The water table is less than 1.0 m below the surface on the extensive mesic meadows on Core Banks.  On these overwash terraces deposited during the 1950s and 1960s, the plant community grades from an open grassland to a closed grassland (Fig 5.9); the standing crop on the latter is up to 30 times that of the open grassland.  Common species on the closed grassland include India love grass (Eragrostis pilosa), fimbristylis, long-awn muhly (Muhlenbergia capillaris), finger grass (Eustachys petraea), firewheels (Gaillardia pulchella), salt marsh rose-gentian (Sabatia stellaris), and spring ladies' tresses (Spiranthes vernalis).  This is the most diverse habitat on the barrier island.

Godfrey and Godfrey (1976) surveyed many dune slacks--areas they described as depressions protected from salt spray and overwash.  In addition to saltmeadow cordgrass, they found many species of grasses, forbs, and vines, including black needlerush (Juncus roemerianus), big-head rush (J. megacephalus), starbrush white-top sedge (Rhynchospora colorata), seaside knotweed, dayflower (Commelina erecta), Virginia buttonweed (Diodia virginiana), common frog fruit, climbing hempweed (Mikania scandens), and climbing milkweed (Cynanchum angustifolium).

Cumberland Island, Georgia

Along the southeastern Atlantic shoreline, Hillestad et al. (1975) describe 22 plant communities or vegetation types on Cumberland Island.  The predominantly herbaceous communities of the dunes include the dunegrass-forb and dune-shrub communities.  Interdune flats are occupied by the grass-sedge community and shrub thickets (Fig. 5.10).

The dunegrass-forb community occurs on foredunes and low interdunes.  Woody plants are absent from this region of intense salt-aerosol deposition and rapid sand movement.  Common species are seashore paspalum (Paspalum vaginatum), coastal plain pennywort, beach hogwort (Croton punctatus), common frog fruit, seaside broomspurge, dune sandbur (Cenchrus tribuloides), seashore dropseed (Sporobolus virginicus), Russian thistle, beach morning glory, and sea oats.  Hillestad et al. (1975) noted that sea oats is not as important on Cumberland Island as other islands, probably because the plants are heavily grazed by feral ungulates.

The interdune grass-sedge meadow described by Hillestad et al. (1975) can be considered a typical slack environment while the thickets and forest are successional communities that gradually replace the grass-sedge meadow.  These researchers divided the grass-sedge meadow into two phases (high and low) based on topography and fluctuations in the water table.  Low-meadow species include fimbristylis, chufa (Cyperus esculentus), toad rush (Juncus bufonius), salt marsh rose-gentian, India love grass, and starbrush white-top sedge, all of which are tolerant to standing water for infrequent periods (Table 5.4).  The high meadow is distinguished by the presence of Canada horseweed (Conyza canadensis identified as Erigeron canadensis), centipede grass (Eremochloa ophiuroides), and ground cherry (Table 5.4).  The interdune shrub thicket, which is dominated by waxmyrtle, cabbage palm, and live oak (Quercus virginiana), is restricted to sites protected from salt aerosols and near intermittent ponds.

Other Dune-and-Slack Communities

On Fire Island, New York, bearberry (Arctostaphylos uva-ursi) and American beachgrass dominate the dune-and-slack vegetation (Art 1976).  These two species account for more than 60 percent of the total plant cover (Table 5.5).  Dusty miller and northern beach pea are most frequent along the seaward face and the crest of the primary dune.  Other important species are the beach plum (Prunus maritima), northern bayberry, beach heather and the vines, cat greenbriar (Smilax glauca), and Virginia creeper (Parthenocissus quinquefolia).  These species are more common on the lee side of the primary dune.  As noted by Art 1976, (Table 5.5), many species with cover values less than 0.1 percent are likely to be inhabitants of the moister slacks.

Johnson (1981) described the vegetation and ecology of cranberry bogs in the Napeague Dunes near Montauk Point, New York.  These cranberry bogs are found in rounded depressions of varying sizes that are scattered between the dune ridges and high ground occupied by pitch pine or dune heath.  Each bog is surrounded by a ring of shrub thicket.  When the water table was measured 3 or 4 days after rain, it varied from 0 to 35 cm below the surface. 

Johnson (1981) divided the bogs into wet and dry phases.  Characteristic species of the wet bogs are bulrush (Scirpus americanus), Canada rush (Juncus canadensis), royal fern (Osmunda regalis), and moss (Sphagnum sp.).  These plants dominate where the water table was 0 to 27 cm deep.  Club moss (Lycopodium inundatum) and forked rush (Juncus dichotomous) dominate the drier bogs--those with a water table at 25-35 cm below the surface.  The dry bogs are found in shallow blowouts recently formed in the dunes; the soils of these bogs are peaty at the surface (2-15 cm), with a gray sand below. 

Artificial impoundments, moist sand flats, and small scattered depressions within the dunes are important wetland environments on Assateague Island, Virginia (Higgins et al. 1971).  Cardinal flower (Lobelia cardinalis), arrow arum (Peltandra virginica), and alkali bulrush (Scirpus robustus) are common in the shallow impoundments, while duckweed (Lemna minor), greater duckweed (Spirodella polyrhiza), water star-wort (Callitriche heterophylla), and cutleaf water-milfoil (Myriophyllum pinnatum) are characteristic of the deeper impoundments.  Slack communities are included by Higgins et al. (1971) in the dunegrass-shrub community, which is described as low, varying from 1.0 to 2.0 m above sea-level.  Cover of herbaceous plants in this area was 60-70 percent; shrub cover was 20-30 percent.

Large areas of bulrush, turnflower rush (Juncus biflorus), and small spike-rush (Eleocharis parvula) dominate environments where there is standing water during part of the year, or where the water table is at or near the surface.  Higgins et al. (1971) reported that small patches of freshwater marshes occur within the mesic shrub community.  These areas are densely shaded by waxmyrtle; however, the freshwater units may have a nearly continuous cover of saltmeadow cordgrass, marsh fern, red fescue (Festuca rubra), and six-weeks fescue (Vulpia octoflora, identified as Festuca octoflora).

Higgins et al. (1971) also described small sinks in the dunes.  These sinks are similar to those reported by Johnson (1981) for the Napeague Dunes on Long Island.  They are highly variable in floristic composition, with rabbitfoot grass (Polypogon monospeliensis), bulrush, and saltmeadow cordgrass as representative species.  Cranberry and spoon-leaf sundew (Drosera intermedia) occur occasionally.

In the mid-Atlantic area, Boulé (1979) described a swale community with an elevation at or near the water table.  Saltmeadow cordgrass is usually a major component of the flora in these depressions.  Knotroot bristle grass (Setaria parviflora, identified as S. geniculata), seaside broomspurge, and little bluestem (Schizachyrium scoparium, identified as Andropogon scoparius) are dominants that consistently distinguish this community from the dunes and the marshes.  Occasional other species are salt marsh rose-gentian, pink wildbean (Strophostyles umbellata), slender flatsedge (Cyperus  polystachyos, identified as C.  filicinis), broom-straw (Andropogon gyrans, identified as A. elliottii), and fimbristylis. 

Saltmeadow cordgrass and bulrush are consistent dominants in the slack communities along the barrier beaches of the North Carolina-Virginia border (Tyndall and Levy 1978; Table 5.6).  The perimeter of nearly every depression is occupied by northern bayberry; loblolly pine (Pinus taeda), eastern false willow, and black cherry (Prunus serotina) are frequently present (Tyndall and Levy 1978).  Figure 5.11 shows the distribution of the plant associations noted in Table 5.6 in relation to soil moisture in these slacks during the growing season.

Along the Outer Banks of North Carolina, four of the five major habitat divisions that Brown (1959) noted are related to the dune-and-slack environment:  sea beach, dunes (including live [unvegetated, migrating] and grass-covered dunes), sand flats (including interdunal, open-dry, and moist flats), and ponds.  Brown's (1959) descriptions of moist and dry dune flats are sketchy; however, the dry flats are labeled in his photographs.  These flats appear to be washover terraces and could be classified as dry slacks--areas where the water table is approximately 1.0 m below the surface.  The moist dune flats, as described, are depressions within the grasslands.  The extensive list of plants cited as occurring in these flats supports the idea that slack environments are reservoirs of plant species diversity. 

Palustrine Wetlands

Scattered throughout the Outer Banks are freshwater pools and ponds.  Semipermanent and permanent ponds near Cape Hatteras are confined to dune swales formed when Cape Point prograded to the south.  These east and west-trending swales possess many emergent species including cattails (Typha angustifolia and T. latifolia), bulrush, beggar ticks (Bidens sp.), Asian coinleaf (Centella asiatica), many flower pennywort (Hydrocotyle umbellata), saw grass, tearthumb (Polygonum sp.), and black willow (Salix nigra).  Burk (1962) noted that coastal water-hyssop (Bacopa monnieri), white-topped sedge, rushes (Juncus biflorus, J. scirpoides), common frog fruit, bulrush, alkali bulrush, and nodding ladies' tresses (Spiranthes cernua) are characteristic species of environments he termed “interdunal swales.”

Odum and Harvey (1988) described interdunal freshwater wetlands and ponds in Nags Head Woods that are best developed and more persistent in locations where island width and topographic relief are greatest.  Vegetation in these ponds ranges from submerged aquatics such as bladderwort (Utricularia spp.) to swamp trees such as red maple (Acer rubrum).  The interdunal ponds in Nags Head Woods have a recent origin, becoming permanent wetlands only about 400 years ago, and their hydrology is closely linked to the groundwater table (List and List 1988).  Plant and animal species found in these ponds are adapted to variable seasonal and annual moisture conditions ranging from high water to drought.  Intensive research in Nags Head Woods has led to a better understanding of these interdunal wetlands, but the single year of study revealed the inadequacy of a single season or drought period collection of data and emphasized the importance of long-term research and monitoring (Bellis 1988; Davison 1988; List and List 1988; MacPherson 1988; Mayes and List 1988; Schwartz 1988). 

Non-vascular Plants 

Microorganisms have an important functional role in the formation, stabilization and degradation of soil aggregates.  Aggregates composed of fungi, bacteria, actinomycetes, and algae have been found in dune and slack soils.  These non-vascular plants that bind soil particles and contribute to the fertility of the soil are better represented in slacks than dunes.  Non-vascular plants are abundant in dune-and-slack systems along the Atlantic Coast; regrettably, the taxonomic, physiological and ecological features of non-vascular plants have not been well researched.  Both algae and bryophytes are adapted to the more mesic conditions of the slack environment.  Much of the research concerning non-vascular plants has been conducted in Europe; the need for additional study, especially in the United States, is evident. 

Microbial Aggregations

Microbial aggregations increase in number and complexity as dunes mature.  As sand dunes form, bacteria bind sand grains with polysaccharides to form microbial aggregations, create structure in young sands, and increase the water-holding capacity of dune soils.  Microbial aggregations are typically more abundant than fungal aggregates during the early stages of dune succession (Forster 1979), and Forster concluded that microbial aggregations act as important stabilizing agents in sandy soils before higher plants can colonize maturing dunes.

Root microbial aggregates (rm-aggregates) form along root surfaces where sand grains trapped in the root surface and root hairs develop spherical aggregates (Table 5.7).  Sand grains also adhere to decaying organic matter and form debris microbial aggregates (dm-aggregates; Forster 1979).  Pseudomonas and Bacillus spp. are important bacteria in these aggregates; these species produce sticky polysaccharides with which they adhere to the surface of sand grains.   

Forster and Nicolson (1981) studied microbial aggregations in various stages of dune succession in Scotland.  They found that the number of aggregations increased as the dune stabilized and higher plants entered the successional sequence (Table 5.8).  They attributed the initially small number of aggregations in the primary dunes to the unstable sand, extreme temperatures, and high salinities occurring in these environments.  Ecologically, aggregates tend to reduce wind erosion and increase both the moisture content and nutrients in the dune sands (Sutton and Sheppard 1976; Clough and Sutton 1978; Forster 1980).  Determination of the environmental factors influencing the number and size of soil aggregations could provide important insights into the natural processes that regulate the colonization of dunes.

Algae

Algae also aggregate in the dune sands, often with bacterial assemblages.  Algae, by holding water in their cell walls, significantly increase the percentage of water available in the dunes; they also interact with microbial assemblages, usually increasing aggregate stability (Bailey et al. 1973).  Blue-green algae enhance the nitrogen content of dune soils through the process of nitrogen fixation (Forster 1980).  Green algae were most frequently found in aggregates, with Oedogonium sp. and Ulothrix sp. typical representatives.  The blue-green algae nostoc (Nostoc sp.) was also an aggregate species.  

Bryophytes

Like algae and bacteria, bryophytes, as members of the dune-and-slack community, have received scant attention and are often ignored in the collections of flora from Atlantic barrier beaches.  Moul (1969) lists Dicranum scoparium and  Polytrichum commune in the flora of Monomoy Island, Massachusetts.  He also listed Polytrichum piliferum and Ceratodon purpureus as part of the dune flora and Sphagnum spp. and Aulacomnium palustre as members of the slack flora for the northeastern United States.  The bryophyte flora of dunes and slacks deserves considerably more study.

Bryophytes are exposed to the same ecological factors as other elements of the coastal flora, namely sand movement, temperature extremes, and salt aerosols.  Aulacomnium palustre and Polytrichum commune appear unable to tolerate salt aerosols; neither species survived experimental applications of salt aerosols, even with simulated rain.  Necrotic conditions appeared 8 to 11 days after salt aerosols were applied to these species (Boerner and Forman 1975).  The bryophytes studied by Boerner and Forman probably survive in niches where salt aerosol is not a factor in dune ecology (i.e., environmental conditions are similar to more inland habitats).  Gimingham (1948) determined that Barbula fallax and Bryum pendulum are important colonizers on secondary dunes.  These species can continue upward growth when covered by a layer of sand.  

Fungi

Fungi are important components of the soil environment of coastal dune sands.  Like most non-vascular plants studied thus far, fungal hyphae increase in incidence as dunes mature (Sutton and Sheppard 1976).  Nicolson and Johnston (1979) determined that the levels of mycorrhizae change as dune succession progresses.  Forster (1979) finds little evidence of the presence of fungi in embryo dunes, probably because of the environmental stresses associated with water availability, temperature, and salinity.  More stable dunes exhibit greater numbers of fungal aggregations.  Penicillium sp., Fusarium sp., Arthrinium sp., and Glomus fasciculatus (a mycorrhizal fungus) have been identified in dune soils (Clough and Sutton 1978; Forster 1979).  In the dunes at Tentsmuir Fife, Scotland, the actinomycete Streptomyces sp. and the mycorrhizal fungus Glomus are dominant organizers of soil aggregates.  The most common soil actinomycetes identified there are Streptomyces and Nocardia spp. (Forster and Nicolson 1981).

Some species of fungi play an important ecological role in the nutrition of higher plants, whereas other dune plants are susceptible to fungal attack.  Nicolson and Johnston (1979) speculated that mycorrhizal fungi in dune soils provide a network to facilitate nutrient absorption in nutrient-poor environments, and that the soil-binding property of the mycorrhizae promotes stabilization of the substrate.  Amelioration of the extreme conditions experienced in dune soils allows certain higher plants with mycorrhizal associations to thrive in an otherwise inhospitable environment (Lucas et al. 1971). 

In contrast, Marasmiellus mesosporus can kill American beachgrass, sea rocket, purple love grass (Eragrostis spectabilis), Canada horseweed, and panic grass.  Experiments show that sea oats, saltmeadow cordgrass, finger grass, and panic grass are not destroyed by Marasmiellus mesosporus (Warren and Lucas 1975).

Higher fungi are present in dune-and-slack communities; however, floristic studies usually ignore the fungal component.  The otherwise thorough studies of coastal ecosystems of Shackleford Banks (Au 1974), Fire Island (Art 1976), and Cumberland Island (Hillestad et al. 1975) did not reference the fungal component of the flora.  Only a few easily recognized fungi such as earthstars (Geaster sp.) are noted in the literature (Fig. 5.12); additional study concerning the distribution and function of these life forms is necessary.    

Despite the xeric conditions of the sand surface, lichens are frequent components of the dune-and-slack flora.  British soldiers lichen (Cladonia cristatella) and other Cladonia species may be found on the soil surface and attached to flotsam such as driftwood.  Old man's beard lichens (Usnea spp.) are frequently present on branches of dune shrubs, especially beach plum.  Most barrier beach and barrier island floras ignore lichens; a systematic study of the distribution of lichen species and the ecological factors influencing these organisms is much needed.  

Dune-and-Slack Animals

Invertebrates

            In a study of the causes of die out in American beachgrass, Seliskar and Huettel (1993) collected species from seven genera of nematodes in dune substrates: Trilineellus, Meloidogyne, Xiphinema, Longidorus, Pratylenchus, Hoplolaimus, and Helicotylenchus.  Most of these species have been shown to cause suppressed growth and root damage in plant species and could account for the die out of American beachgrass.  Generally, neither intensive nor extensive studies of many invertebrate groups living in dune-and-slack environments have been undertaken.

Similarly, terrestrial gastropods have received little attention in coastal environments.  At Cumberland Island, Georgia, Hillestad et al. (1975) note that Lymnaea humilis and Succinea campestris are the dominant gastropods in the low moist interdune flats.  Eight other species of gastropods were found on Cumberland Island; however, none of these were reported as members of the dune-and-slack fauna.  Although not a dominant group of dune-and-slack species, terrestrial gastropods deserve further study in the upland, semi-aquatic, and freshwater coastal settings. 

Arthropods are an important biotic component of dune-and-slack communities.  McLachlan et al. (1987) measured biomass of insect inhabitants of dunes along the South African coast and found that seven insect orders were present.  Grasshoppers (Orthoptera) were most common, but beetles (Coleoptera) contributed the greatest biomass of the insect fauna.  Butterflies (Lepidoptera), especially their larvae, also were common.  Aphids (Homoptera), flies, (Diptera), bees (Hymenoptera), and earwigs (Dermaptera) were present, but in lesser numbers.  Insects are most common in mature dune plant communities.

Although present, insects are not abundant in the open-sand habitat.  Curiously, the presence of marram grass (Ammophila arenaria) in the embryo dune area of the backshore depresses the arthropod population even more (Slobodchikoff and Doyen 1977; Fig. 5.13).  The dense mat of roots created by dune vegetation may reduce the numbers of burrowing arthropods, and food may be less available.  The tender parts of marram grass are well above the sand surface compared with sprawling plant species that have tender shoots nearer the surface.  An alternate hypothesis suggests that dense clumps of dune grasses may reduce the temperature of the soil near the surface.  Although Slobodchikoff and Doyen's (1977) study was conducted on dunes almost exclusively dominated by marram grass, a native of Europe, similar results are likely in dense monospecific stands of American beachgrass on the Atlantic Coast.

On Cumberland Island, Georgia, more than 20 species of ground beetles (Carabidae) have been collected; Omophorn labiatus was the most common species (Hillestad et al. 1975). These species were collected in the largest numbers in wet and dry phases of the interdunal grass-sedge flats.  Wagner (1964) reported that two species of beetles Collops nigriceps (Melyridae) and Isomira sp. (Alleculidae) were commonly collected in association with flowering spikelets of sea oats.

Mallow et al. (1984) recovered more than 6,000 microarthropods, representing 120 genera in 80 families of mites and collembolans, in the dune soils on Jekyll Island, Georgia.  Samples were taken from an ecotone between the herb-dominated foredunes and forested dunes.  The population densities of these organisms are comparable with those reported for deciduous forests and temperate grasslands and greater than those reported for deserts and salt marshes.  Among the major suborders of mites, Cryptostigmata and Prostigmata are the dominant groups, with densities of 60-74 percent and 12-27 percent, respectively, of all individual microarthropods collected by Mallow et al. (1984) (Fig. 5.14).  The authors stress that further investigation is necessary to determine the role of this fauna in dune stabilization.

The distribution of the arachnid population on dunes reflects the xeric conditions found in these environments.  Barnes (1953) studied spiders on dune vegetation, the soil surface, and the subsurface.  Four species of spiders, Tibellus duttoni, Hyctia pikei, Larinia directa, and Eustala anasera, inhabited the herbaceous vegetation on the dune.  Nine ground-dwelling species of spiders were collected from the dune surface.  Trochosa shenandoa, Castianeira sp., and Schizocosa salsa were predominant in this niche.  In contrast, nearly twice as many species (21) of subsurface‑dwelling spiders were collected in the dunes.  Clubiona plumbi, Ariadna bicolor, and Grammonota sclerata were the most abundant species in the subsurface niche.

The spider fauna is similar in the strandline and the dunes.  Grammonota sclerata and Clubiona plumbi, two species adapted to xeric conditions, are common in both habitats.  These species migrate out of the drift and onto the adjacent beach to feed, primarily at night.

Amphibians

Amphibians are represented in the smallest numbers of the vertebrates on barrier beaches, certainly because of the xeric conditions of the dunes.  Engels (1952) found only five amphibian species on Shackleford Banks.  These five represent only 15 percent of the amphibian species found on the nearby mainland; Gibbons and Harrison (1981) found a similar relationship between the mainland and Kiawah and Capers islands, South Carolina.  For Cumberland Island, Georgia, an island not only larger than Shackleford Banks, North Carolina, but also with more extensive forest and freshwater environments, Hillestad et al. (1975) reported 18 species of amphibians.  Seven species of amphibians are reported from Kiawah Island, South Carolina, and four species from Capers Island, South Carolina (Gibbons and Harrison 1981).  The slack environments are more hospitable to populations of amphibians, but ecological studies that focus on this group are lacking. 

Fowler's toads (Bufo woodhousei fowleri) (Fig. 5.15) are common in dunes and slacks on Shackleford Banks and northward (Engels 1952).  South of Cape Hatteras, North Carolina, the southern toad (Bufo terrestris) and the eastern spadefoot toad (Scaphiopus holbrooki) may be present.  Narrow-mouthed toads (Gastrophryne carolinensis) and grass frogs (family Hylidae) are found in a diversity of coastal habitats and may occasionally occur in slacks.

Reptiles

Like the amphibians, the reptile fauna on barrier islands in general, and dunes-and-slack systems in particular, is depauperate.  Most populations of snakes and lizards collected on mainland beaches, barrier beaches, or barrier-island systems reflect the local availability of suitable habitats.  No endemic species of reptiles (or amphibians) have been described for any single island or group of Atlantic Coast barrier islands (Gibbons and Coker 1978).

On islands distant from the mainland, subspecies are likely to form.  The island form of the coachwhip (Masticophis flagellum) often exhibits a light‑ to dark‑tan tail; the tail of the mainland coachwhip is uniformly black.  Lazell and Musick (1973) described a subspecies of kingsnake, Lampropeltis getulus sticticeps, found only in the intra-Capes ecological zone between Cape Lookout and Cape Hatteras, North Carolina.  On the other hand, Hillestad et al. (1975) did not uncover any insular races of reptiles or amphibians, and Gibbons and Coker (1978) concluded that no endemic species of reptile or amphibian has been reported for any North American barrier island.

On the Outer Banks of North Carolina, Lazell and Musick (1973) found herpetofauna with northern affinities.  They argued that migration of snake and lizard populations down the Outer Banks from the mainland of Virginia is easier than migration northward from Bogue and Shackleford Banks, North Carolina.

Other typical dune-and-slack species include the black racer (Coluber constrictor), the common garter snake (Thamnophis sirtalis), and the eastern ribbon snake (T. sauritus).  These species are reported from Cape Cod to at least the coastal islands of Georgia.  Six-lined racerunners (Cnemidophorus sexlineatus) and the Eastern glass lizard (Ophisaurus ventralis) are common in southeastern dune environments.  Engels (1952) noted that ". . . no [racerunners] were seen in damp or marshy ground, although, on the flats, they were seen right up to the dry, sandy edge of shallow pools and marshes, within a few inches of the water."

Turtles encountered in the dune-and-slack community are probably transients.  Diamondback terrapins (Malaclemys terrapin) have been observed in mesic meadows on Core Banks; these specimens probably entered the meadows from nearby tidal creeks.  The common box turtle (Terrapene carolina) is the only other species apt to inhabit the dune-and-slack environment. 

The loggerhead sea turtle (Caretta caretta) nests annually on the backshore and foredunes of beaches and barrier islands from Cape Fear, North Carolina, south to Cape Canaveral, Florida (and southward), and nests infrequently north from Cape Fear, North Carolina, to Assateague Island, Virginia.  Female loggerhead sea turtles occasionally wander into the dunes and slacks in search of a suitable nesting site.

Birds

Engels (1942, 1952) summarized his barrier island faunal work by noting that it was difficult to describe a distinct suite of species characteristic of, or peculiar to, dune-and-slack systems along the Atlantic Coast.  Engels concluded that many species may use resources from dune-and-slack environments, but very few live all, or even a majority, of their lifespans in the dunes and slacks.  This is a very narrow view considering the large number of species, especially shorebirds and waterbirds, that depend upon barrier beaches as primary nest sites or have a crucial life stage that depends upon the availability of this habitat.  

Terns and gulls may use the strandline, back-barrier beach, and sand flats within dune systems for nesting and resting.  These species usually select open environments that lack plant cover.  In contrast, willets (Catoptrophorus semipalmatus) typically nest in clumps of dune grasses (Fig. 5.16), and black ducks (Anas rubripes) may nest wherever sufficient cover is available, including dune-and-slack environments.  Eastern meadowlarks (Sturnella magna), common nighthawks (Chordeiles minor), common ground-doves (Columbina passerina), and mourning doves (Zenaida macroura) nest within the dunes and feed on insects or seeds of dune plants.  Boat-tailed grackles (Quiscalus major) feed primarily on insects and crustaceans but may eat the seeds of sea oats during the fall and winter months.  Birds of the forest or shrub community--gray catbird (Dumetella carolinensis), brown thrasher (Toxostoma rufum), northern mockingbird (Mimus polyglottos), and rufous-sided towhee (Pipilo erythrophthalmus)--may occasionally forage in dune-and-slack communities.

Predatory birds may feed within the backshore, dune-and-slack communities.  Fish crows (Corvus ossifragus), peregrine falcons (Falco peregrinus), American kestrels (Falco sparverius), and short-eared owls (Asio flammeus) search coastal habitats--including the dune-and-slack communities--for prey.  The bald eagle (Haliaeetus leucocephalus) and northern harrier (Circus cyaneus) may search for prey in dune, slack and backshore environments.  

The piping plover (Charadrius melodus), a federally threatened species, forages along beaches and sandy shores for small invertebrates that it picks up with its short bill.  Piping plovers nest on sandy beaches and sand flats along the Atlantic Coast from Canada south to North Carolina (Haig and Oring 1985; Fig. 5.17).  The plover winters along the Gulf of Mexico and the southern Atlantic Coast from Florida to North Carolina.

Colony nesting species, including royal terns (Sterna maxima), common terns (Sterna hirundo), gull-billed terns (S.  nilotica), and black skimmers (Rynchops niger), used barrier beaches and sand flats extensively as nest sites until driven to other habitats (e.g., dredge-deposit islands) by extensive human development of the barrier islands (Erwin 1980; Burger 1981; Parnell and Shields 1990).  The least tern (Sterna albifrons) continues to nest on sand flats and embryo dune environments on barrier beaches.

Mammals

The mammal fauna of Atlantic barrier beaches has been studied by several researchers (Paradiso and Handley 1965; Pelton 1975; Andre 1981; Webster 1988).  Like reptiles and amphibians, the dispersal of mammal populations is slowed by significant geographic barriers.  Because tidal marshes, creeks, and inlets are formidable barriers to migrating small mammals, mammalian diversity is typically low on barrier islands.  Engels (1952) reported that only one-quarter of the mammal species present on the mainland were also present on Shackleford Banks, North Carolina. 

Dueser et al. (1979) studied the mammals on an 87-km section of the Virginia barrier islands from Wallops Island to Fisherman's Island.  Sixteen mammal species, eleven native and five introduced, were collected (Table 5.9).  Most of those species collected were inhabitants of marshes, forests, or old fields; however, the house mouse (Mus musculus), raccoon (Procyon lotor), white-tailed deer (Odocoileus virginianus), red fox (Vulpes vulpes), and an introduced species, black-tailed jackrabbit (Lepus californicus), may use dune-and-slack habitats for denning or foraging.  The gray fox (Urocyon cinereorgenteus) is common on beaches, dunes, and herb-shrub habitats in the Cape Hatteras National Seashore (Parnell et al. 1992).   The species and numbers of mammals present on specific islands are highly variable.  Because each species differs in its ability to reach the various barrier islands, the number and diversity of mammals found in dune and slack communities between Cape Cod, Massachusetts and Cape Canaveral, Florida, is highly variable.

Species most often encountered on dunes along the northern Atlantic Coast are the white-footed mouse (Peromyscus leucopus), the meadow vole (Microtus pennsylvanicus), the meadow jumping mouse (Zapus hudsonius), the masked shrew (Sorex cinereus), and the house mouse.  Shure (1970) reported large populations of these species on Island Beach, New Jersey, and attributed the abundance of small mammals to the heterogeneity of vegetation and abundant, high-quality food sources on the island.  Few small mammals forage in the sparse cover of the highest dunes; white-footed mice are increasingly common in the shrub-dominated slacks landward of the primary dunes and in the secondary dunes dominated by beach heather.  The meadow vole and meadow jumping mouse were present in small numbers in these slacks.  Overall, as shrub cover increased, the density and diversity of small mammals increased (Shure 1970).

Despite extensive studies of the fauna of Atlantic Coastal environments, considerable work remains.  Studies of many invertebrate groups, including molluscs and arthropods, are lacking.  The herpetofauna, although known on many islands, has yet to be studied with the thoroughness and in the context necessary to provide an understanding of its insular life history phenomena (Gibbons and Coker 1978).  

Rare and Endangered Animals 

The rare or endangered animals of the coastal zone are not typical inhabitants of the dune-and-slack community, although these animals may use some resources from this part of the coastal environment.  Female loggerhead sea turtles frequently nest in the foredune environment.  As development proceeds and the number of suitable nesting beaches on the Atlantic Coast declines, the loggerhead turtle population may continue to decline.

Nesting piping plovers face several threats to their continued existence.  Recreational use of shorelines has directly contributed to the decline in the number of individuals of this species (Haig and Oring 1985).  Foot and vehicle traffic reduces the ability of these species to successfully forage; summer storms and other high tides may wash out piping plover nests.  Eggs and young are easy prey for raccoons, foxes, and feral cats.  Least terns experience similar pressures while nesting in the strandline and embryo dune environments.  

Exotic Species

Exotic species of plants and animals introduced to coastal dune-and-slack environments may successfully establish breeding populations.  Exotic organisms infrequently thrive in unfilled ecological niches in the dune-and-slack system.  Japanese sedge (Carex Kobomugi), a species believed to have been introduced in the Northeast United States more than 60 years ago (Natural Lands Management 1984), has maintained populations on barrier dunes.   Japanese sedge was uncommon on the dunes near Virginia Beach, Virginia, until 1980 when a coal mine strike resulted in more than 100 colliers anchoring at the mouth of the Chesapeake Bay.  Many of these ships secretly pumped effluent overboard.  Many northeasters in the winter of 1980 pushed this “fertilizer” onto the foredune of Seashore State Park, and the plant spread rapidly after that (Wright et al. 1990).  French tamarisk (Tamarix gallica) and Japanese black pine (Pinus thunbergiana) are plants introduced on coastal dunes along the Atlantic Coast; however, these and many other exotics have not spread very far beyond their original plantings and have not caused significant changes in coastal communities.

Recent floristic studies show significant changes in species presence in coastal environments.  Recreational use of state and national parks has increased as tourist amenities have been expanded; visitation leads to the spread of vascular plants.  For example, 104 non-native species of vascular plants have been introduced to Orient Beach State Park on Long Island, New York, since 1934, and alien plants compose 44 percent of the flora (Lamont and Stalter 1991).  Ecological studies concerning the effects of exotic plants and animals on the structure and function of coastal dune-and-slack systems are wanting.

Domesticated animals have affected the coastal dunes and slacks, especially where overgrazing has occurred.  Feral hogs were introduced into Florida and Georgia by the Spanish in the 1540’s and they were introduced some time later into coastal South Carolina and North Carolina (Mayer and Brisbin 1991).  Hogs in southeastern Virginia were introduced during English settlement.  The areas of Back Bay National Wildlife Refuge and False Cape State Park, Virginia, and Currituck Banks, North Carolina, had open range in the 1920’s and 1930’s.  Today, populations of feral hogs persist on the Back Bay area of Virginia and Cumberland Island, Georgia; these animals root in herbaceous wetlands, altering the substrates and causing measurable changes in species composition.  Feral horses on barrier islands from Maryland to Georgia graze in interdune meadows or slacks, visibly altering this vegetation type.  Cattle, sheep, and goats were common grazers in the dune-and-slack community until the 1950’s; today, these animals have been removed from almost all barrier beaches.  Feral cats remain pests on Cape Hatteras and Cumberland Island national seashores (Parnell et al. 1992; Hillestad et al. 1975).

Feral populations of nutria (Myocaster coypus) are established in fresh and brackish wetlands from Maryland to North Carolina where they feed on a variety of plants including giant cordgrass (Spartina cynosuroides) and Olney's bulrush (Scirpus americanus, identified as Scirpus olneyi) (Wilner 1982).  Nutrias occasionally forage in dune slacks, especially those with nearby cover.

Ecological studies of coastal species have been directed at dominant or unique species of plants and animals.  Much more research is necessary to determine the role that minor species play in the dune-and-slack system.  Life history studies are likely to show that some species considered minor or unimportant have an impact much greater than their visual presence in dunes and slacks.  

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