Grey dunes are fixed, stable Dune that are covered by a continuous layer of Herbaceous plant. These dunes are typically located 50–100 meters from the ocean shore and are found on the landward side of foredunes (also known as ). Grey dunes are named for their characteristic grey color which is a result of the ground cover of lichen combined with a top soil layer of humus.
Formation
Grey dunes are formed when
pioneer species inhabit
embryo dunes and begin a successional process toward dune stabilization and
soil formation. Pioneer plants capture saltating sand grains carried by the wind and deposit them to continue build up the dune. Grey dunes are then formed after the root structures of pioneering plants stabilize
foredunes. Sand stabilization allows for dead plant material to be decomposed within the soil, adding nutrients and water-retention abilities to the soil.
As soil starts to slowly form, new plant species colonize the stable dunes ultimately developing more extensive root structures and plant diversity.
When the dune has become continuously vegetated,
lichen and
moss grows in the
understory, providing a water-repellent surface that reduces
erosion (through rainfall and wind), this results in the official formation of the grey dune.
Pluvial processes dominate the geomorphology of grey dunes, with rain splash and slope wash being the most common processes taking place. Erosion can take place in the form of rain splash and slope wash.
Dune pH
Depending on the sand composition, a grey dune will become either
acidic or
calcareous. An acidic soil substrate will form if the sand is composed completely of
quartz grains. Older grey dunes can also exhibit acidic conditions if there has been enough rainfall to leach out the soil nutrients. Calcareous soil substrates form when seashells decompose to create a lime-rich environment.
The vegetation on grey dunes is dependent on the pH of the soil substrate.
Vegetation
Many
Rare species and
endangered plant species can be found within grey dune ecosystems, providing
Ecological niche for animals and insects. A wide variety of
orchids,
grasses, and
lichens are found in grey dune plant communities but species will depend on locations throughout the European continent.
Location
Grey dunes are found along much of the
coast and along large, inland bodies of water. Broadly speaking, they can be found along the
Celtic Sea,
Baltic Sea, and
North Sea Seas, the Eastern and Mid
Atlantic coast, the Western and Eastern
Mediterranean coasts, and the
Black Sea.
Loss of Grey Dunes
Grey dunes are highly susceptible to change from both natural and human-induced events. Since the 1960s, grey dune ecosystems have declined from the encroachment of
grass and
shrub species, and more recently, by the invasion by the alien invasive Heath Star Moss (Campylopus introflexus). Causes of the encroachment have been related to large-scale sand dune stabilization, high
nitrogen deposition from the vegetation, and a decline in
rabbit populations within the dunes.
Grass and shrub encroachment has resulted in the fragmentation of grey dune landscapes (and overall reduction in habitat), a loss of biodiversity, and a decline of
endangered and
rare species that are endemic to grey dunes.
See also
-
Kilmuckridge-Tinnaberna Sandhills
-
Foredune
