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Characteristic dune formation
requires the presence of a large sand supply, wind, and substrate for the
sand to accumulate. Dunes formation is subject to an accretion and erosion
cycle that is dependent on seasonal wave heights and dominant wind
directions. Sand is eroded and carried to offshore bars in the winter.
Constructive waves then move the sand from the bars onto the intertidal
beach during the summer. With the presence of a dominant onshore wind this
sand is then carried landward and collects around debris and emerging
tolerant plant species.
Dune systems can
be divided into three zones: (1) strandline and embryo dune zone, (2)
primary dunes, and (3) secondary dunes. The strandline forms when beach
debris is carried by spring tides to the backbeach environment. This
collection of debris then provides substrate for the accumulation of sand.
This first stage of dune development, with the presence of dune building
plant species (Sea Rocket, Euphorbia, Sea Elder, Croton, and Sea Oats),
will, overtime, develop into a continuous dune ridge parallel to the
shoreline. With the availability of abundant sand and colonizing
vegetation, this high continuous ridge will become the primary dune. The
colonizing plant species of the primary dune (Sea Elder, Sea Oats, Bitter
Panicum, and American Beachgrass) must be tolerant to sea spray and
constant burial. Secondary dunes are those dunes landward of the primary
dunes that were once considered primary dunes prior to new embryonic dune
formation. These dunes are remote from the foreshore source of sand and
are not subject to an extreme saline environment as a result of
established vegetation. This interaction of coastal geological and
biological processes creates a diverse system of barrier dune communities. |
Dune Ridge |
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