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
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Barrier Island Dunes and Slacks
Vegetation Zones Strandline Foredune Dunef
ield Reardune Mesic slack Xeric slack
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Strand Line

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

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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

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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

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Formation of Embryonic Dune

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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

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Dune Pioneer

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

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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

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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

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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

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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

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Mesic Slack

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

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Xeric Slack

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

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Coastal Plant Geography

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

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Vascular Plant Families

• Families most represented

Asteraceae- Salt Marsh Aster
Cyperaceae- Saltmarsh Bulrush
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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

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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

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Coastal Plant Geography cont...

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

Sea elder ? southward
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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

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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

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Rare and Endangered Plants

• Massachusetts
• Seaside knotwood- common species

• North Carolina
• Seaside knotwood- candidate
• for listing as either threatened
• or endangered

Knotweed, Polygonum glaucum
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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

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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

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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

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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

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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

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Fungi


Mycorrhizal fungi of root system
Azospirillium induces proliferation at root hair
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Exotic Species

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

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Animals

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

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Invertebrates
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
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Nematodes and Arthropods
Ground beetle
Beachgrass root-knot nematode
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More invertebrates...
Monarch Butterfly
Ghost Crab
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Amphibians

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

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Reptiles

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

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Reptiles

• Turtles Those seen are probably transients

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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
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Birds

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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 ?

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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

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Rare and Endangered Animals

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

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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
  1950s
• Feral horses persist on islands from MD to GA

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References
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.
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