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Dunes and Slacks Dune: Mound of wind blown sand often influenced by vegetation Slack: Low depression formed during dune development or by blowouts in the dune field Barrier Island Dunes and Slacks Vegetation Zones: Strandline Foredune Dunefield Reardune Mesic slack

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Dunes and Slacks

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Dunes and Slacks

Dune:Mound of wind blown sand often influenced by vegetation

Slack: Low depression formed during dune development or by blowouts in the dune field


Barrier Island Dunes and Slacks

Vegetation Zones:





Mesic slack

Xeric slack


Strand Line

  • seaward line of vegetation occurring between the spring tidal elevation and the foredunes

Strand Line

  • transient zone- eroded by wave action or may develop into foredunes on accreting shorelines
  • seedbed for plants on foredunes
  • wrack material enhances germination and growth
  • salt aerosol levels are high
  • sea rocket, euphorbia, sea elder, croton, and sea oats

Sea Rocket

Strand Line Community

  • Plants: trap wind-blown sand and form embryonic dunes
    • Sea rocket is most common species along Atlantic coast
    • Other species:
    • Eelgrass (dead stems and leaves), smooth cordgrass (dead stems and leaves), Russian thistle, and seasside broomspurge

Strand Line Community

  • Over time:
    • Nutrient source becomes limited
    • Environmental conditions change
    • Vegetation cover begins to change:
    • Strand Line species replaced by  Dune Pioneers
    • Russian Thistle Sea Elder
    • Evening Primrose Sea Oats
    • Sea Rocket Am. Beachgrass

Dune Pioneer

  • Sea Oats- restricted to dunes:
  • extreme conditions of wind-blown salt
  • shifting sand- allows for burial and excludes competition


  • occur directly behind the strand line
  • often receive large quantities of blowing sand
  • sea oats, sea elder, bitter panicum and American beachgrass
  • salt aerosol levels are high


  • may consist of many dune ridges that were once foredunes
  • sand accretion is low
  • reduced salt spray intensity
  • camphorweed, pennywort, evening primrose, and horseweed


  • often a transition zone to woody vegetation
  • salt spray effect diminished
  • catbrier, live oak, wax myrtle, and red bay
  • destruction of the dunefield/foredune zones will severely impact vegetation in the reardune


  • low depressions formed during dune ridge development or by blowouts in the dune field
  • salt spray intensity is low
  • greater diversity of species
  • increased plant cover density
  • may be destroyed by migrating sand dunes

Mesic Slack

  • water table is at or near the surface during part of the year
  • pennywort, little blue stem, seaside goldenrod and wax myrtle

Xeric Slack

  • water table close to surface compared to dunes allowing a greater number of species to develop
  • pennywort, saltmeadow cordgrass, and camphorweed

Evening primrose

Seaside goldenrod

Coastal Plant Geography

  • Distribution influenced by climate: Tº and precipitation
  • Adapted for rapid dispersal and colonization
  • Most occur over broad geographical range

Poaceae- Sea Oats

Vascular Plant Families

  • Families most represented:

Asteraceae- Salt Marsh Aster

Cyperaceae- Saltmarsh Bulrush


Coastal Plant Geography cont...

  • Small (1929)
  • Southern New Jersey and Delmarva Peninsula is meeting ground for N & S plants
  • Supported by:
  • Higgins et al. 1971- found bitter panic grass near its northern limit on Assateague Island, VA
  • Martin (1959)- Panic grass absent at Island Beach, NJ

Southern limit: American beachgrass

Northern limit: Sea oats

Coastal Plant Geography cont...

  • Oosting (1954) and Godfrey (1977):
  • - Consider NC the dividing line for N &S strand communities
  • - Godfrey notes a Tº break at Cape Hatteras, NC and:

Northern beach pea  southward

Coastal Plant Geography cont...

  • Art (1976)- Opposed Small’s viewpoint
    • Atlantic coast plant species are gradually replaced along a latitudinal gradient

Sea elder  southward


Prickly pear cactus- found here but not to the north

  • Northern bayberry- absent but common to the north

Coastal Plant Geography cont...

  • Lazell and Musick (1973)
  • Intra-Capes ecological zone- b/w Cape Lookout and Cape Hatteras, NC; transition zone for many species

Rare and Endangered Plants

  • New Jersey:
  • Seaside broomspurge- rare in NJ, yet abundant in southeast
  • Seabeach sandwort- endangered in NJ, more common to the north

Rare and Endangered Plants

  • Massachusetts:
  • Seaside knotwood- common species
  • North Carolina:
  • Seaside knotwood- candidate
  • for listing as either threatened
  • or endangered

Knotweed, Polygonum glaucum


Non-vascular Plants

  • More important in slacks
  • Microorganisms have an important role in soil formation
  • Aggregates found in dune and slack soils: Fungi, bacteria, actinomycetes, and algae
  • These plants bind soil particles and increase soil fertility
  • Little is known of these plants- future research warranted

Non-vascular Plants

  • Microbial aggregations
    • Increase in number and complexity as dunes mature
    • Bacteria binds sand particles to  water-holding capacity
    • 2 types:
    • Root microbial aggregates- Sand grains trap in root surface and hairs
    • Debris microbial aggregates- Sand grains adhere to decaying organic matter to form these

Ulothrix sp.

Oedogonium sp.

Non-vascular Plants

  • Algae
    • Often aggregate with bacteria
    • Hold water within their cell walls
    • Interact with microbial aggregates and improve stability
    • Blue green algae enhance nitrogen content of soils

Non-vascular Plants

  • Bryophytes- Moul (1969) and Gimingham (1948)
  • Little research has been done
  • Found in both dunes and slacks
  • Relatively intolerant to aerosol salt spray
  • Important colonizers of secondary dunes

Non-vascular Plants

  • Fungi- Nicholson and Johnston (1979)
    • Little research has been done
    • Increase in incidence as dunes mature
    • Some play a role in nutrition of higher plants
    • Some plants are susceptible to fungal attacks


Mycorrhizal fungi of root system

Azospirillium induces proliferation at root hair


Exotic Species

  • Plants: may establish breeding populations
  • Accidentally introduced by tourists
  • Few survive and thrive in dunes and slacks
  • Japanese sedge
  • French tamarisk


  • Invertebrates
  • Amphibians
  • Reptiles
  • Birds
  • Mammals
  • Rare and endangered species
  • Exotics


  • Nematodes:
  • Suppress growth and cause root damage to plants
  • Cause die offs of American Beachgrass
  • Arthropods:
  • McLachlan et al. (1987) found 7 orders of insects in study along African coast
  • Insects most common in mature dunes
  • Mostly found in open sand habitat

Nematodes and Arthropods

Ground beetle

Beachgrass root-knot nematode


More invertebrates...

Monarch Butterfly

Ghost Crab


Fowler’s toad- common in dunes and slacks near Shackleford Banks, NC

Southern toad- southward of Cape Hatteras, NC


  • Least represented vertebrate in dunes and slacks
  • Found primarily in slacks
  • Common species:

Black racer snake

Common garter snake

Eastern ribbon snake


  • Poorly represented on barrier beaches
  • Most common species from Cape Cod to Georgia:
    • Snakes:

Diamondback terrapin

Common box turtle

Loggerhead sea turtle


  • Turtles: Those seen are probably transients


  • Many species use dune and slack resources
  • Few live entire lifespan in this area
  • Mostly use dunes and slacks for nesting or feeding sites

Terns and gulls use strand line and sand flats

Willit- nest in clumps of dune grasses

Piping Plover- federally threatened forages along beach for small inverts


Royal Tern


Piping Plover



Meadow vole

White footed mouse


  • Species diversity is typically low
  • Most are inhabitants of marshes, forests, or old fields
  • As shrub cover  density and diversity of small mammals also 

Rare and Endangered Animals

  • Not typical inhabitants of dunes and slacks
  • Loggerhead sea turtles- use resources to nest
  • Coastal development decreases number of suitable nesting beaches

Piping Plover

Least tern

Rare and Endangered Animals

  • Piping plovers and least tern-
    • Recreation impacts nesting and foraging success
    • Storms and predators lower nesting success

Exotic Species

  • Animals: Introduced domestics
  • Overgraze and alter substrates
  • Hogs persist on Back Bay area, VA and Cumberland Island, GA
  • Cattle, sheep, and goats were common until the 1950’s
  • Feral horses persist on islands from MD to GA


  • Amos, W. H. and S. H. Amos. 1985. National Audobon Society Nature Guides:Atlantic and Gulf coasts. Random House: New York, NY: 670p.
  • Graetz, K. E., 1973. Seacoast Plants of the Carolinas. U. S. Department of Agriculture Soil Conservation Service, Raleigh, North Carolina, 206 pp.
  • Environmental Inventory of Kiawah Island, 1975. Environmental Research Center, Inc., Columbia, South Carolina.
  • Kraus, E. Jean Wilson, 1988. A Guide to Ocean Dune Plants Common to North Carolina. The University of North Carolina Press, Chapel Hill, North Carolina, 72 pp.
  • Packham, J. R., and A.J. Willis. 1997. Ecology of dunes, saltmarsh and shingle. Chapman and Hall: Cambridge: 335pp.
  • Shumway, Scott W., 2000. Facilitative effects of a sand dune shrub on species growing beneath the shrub canopy. Oecologia (2000) 124: 138- 148.
  • Will, M. E., D. M. Sylvia, 1990. Interaction of Rhizosphere Bacteria, Fertilizer, and Vesicular-Arbuscular Mycorrhizal Fungi with Sea Oats. Appl. Environ. Microbiol., July 1990, p. 2073-2079.

References cont...