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

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

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

Sea Rocket

Formation of Embryonic Dune

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

Foredune

• 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

Dunefield• may consist of many dune ridges that were once foredunes

• sand accretion is low

• reduced salt spray intensity

• camphorweed, pennywort, evening primrose, and horseweed

Reardune• 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

Slacks

• 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

Coastal Plant Geography

• Distribution influenced by climate: Tº and precipitation

• Adapted for rapid dispersal and colonization

• Most occur over broad geographical range

Seaside goldenrodEvening primrose

Vascular Plant Families• Families most represented:

Poaceae- Sea Oats

Cyperaceae- Saltmarsh Bulrush

Asteraceae- Salt Marsh Aster

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

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 limit: Sea oats Southern limit: American beachgrass

Coastal Plant Geography cont...

• Art (1976)- Opposed Small’s viewpoint

Atlantic coast plant species are gradually replaced along a latitudinal gradient

Northern beach pea southward Sea elder southward

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

Prickly pear cactus- found here but not to the north

Northern bayberry- absent but common to the north

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

• North Carolina:

Seaside knotwood- candidate

for listing as either threatened

or endangered

• Massachusetts:

Seaside knotwood- common species

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

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

Ulothrix sp. Oedogonium sp.

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

Fungi

Azospirillium induces proliferation at root hair

Mycorrhizal fungi of root system

Exotic Species • Plants: may establish breeding populations

• Accidentally introduced by tourists

• Few survive and thrive in dunes and slacks

Japanese sedge

French tamarisk

Animals• Invertebrates

• Amphibians

• Reptiles

• Birds

• Mammals

• Rare and endangered species

• Exotics

InvertebratesNematodes:

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

Beachgrass root-knot nematodeGround beetle

More invertebrates...

Monarch Butterfly

Ghost Crab

Amphibians• Least represented vertebrate in dunes and slacks

• Found primarily in slacks

• Common species:

Southern toad- southward of Cape Hatteras, NC

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

Reptiles• Poorly represented on barrier beaches

• Most common species from Cape Cod to Georgia:

Snakes:

Black racer snake

Common garter snake

Eastern ribbon snake

Reptiles• Turtles: Those seen are probably transients

Diamondback terrapin

Loggerhead sea turtle

Common box turtle

Birds• 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

Birds

Royal Tern

Willit

Piping Plover

Mammals • Species diversity is typically low

• Most are inhabitants of marshes, forests, or old fields

• As shrub cover density and diversity of small mammals also

White footed mouseMeadow vole

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

Rare and Endangered Animals • Piping plovers and least tern-

Recreation impacts nesting and foraging success

Storms and predators lower nesting success

Piping Plover Least tern

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

ReferencesAmos, 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...

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