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Coastal Sand Dunes

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Coastal sand dunes form where a beach is big enough to allow the sand to completely dry out between high tides, and where there are onshore winds to blow the dry sand landwards. The sand is then trapped by dune grasses which grow through the accumulating layers of hard, inorganic sand.

In young dunes, there are very few nutrients available because no plants have yet colonised the dune and died, meaning there is no organic matter being recycled within the sand. However, there are some dune pioneer plants which are able to partially overcome this problem through being able to store nitrogen in their roots.

Historical info about Coastal Sand Dunes

The dunes around Northern Ireland were formed thousands of years ago - the Northern Ireland Habitat Action Plan for Coastal Sand Dunes states that the dunes between Lough Foyle and the Bann Estuary are approximately 3000 years old. The largest dune system in Northern Ireland is at Murlough in Co. Down is reckoned to be between 5000 and 6000 years old.

Species living in and around Coastal Sand Dunes

Sand dune vegetation varies widely and is related to the length of time since the sand was deposited, how stable the area is and other local conditions. Some dunes support very little vegetation, whereas others support a wide range of plant life. One of the first plants to colonise a sand dune system is usually marram grass (Ammophila arenaria) as it has a deep vertical root system and has can keep up with the speed of the sand being deposited. Over time other plants will colonise, such as sea holly, sea bindweed, sea spurge. Heavily grazed acidic dunes can support lichen. Various mosses and creeping willow can also be present.

The extent of the biodiversity in Murlough Bay in Co. Down.
Species Number of different species (and percentage compared to the whole Irish fauna)
Bee, ant and wasp 55 (33%)
Moth 213 (48%)
Butterfly 21 (71%)

Threats to Coastal Sand Dunes

Degradation of sand dunes is caused by many different factors:

  • Erosion - caused by insufficient sand blowing back over the dunes.
  • Fall in the water table - if the water level falls over a prolonged period of time, it can adversely affect the specialised plants around the hollows in the sand dunes (slacks).
  • Overgrazing - while some level of grazing is necessary to control the vegetation and is, in fact, one of the main management techniques for sand dunes, overgrazing is a problem as it can free space for coarse grasses and scrubs and make the dune unstable and more prone to erosion.
  • Recreational Use - golf courses, visitors and holiday-makers, coastal sea defence and military use causes damage on plant life on sand dunes.
  • House and industrial development as well as beach management with mechanical tools and waste disposal can create problems such as a loss of the vegetation that protects the surface of dunes.
  • Invasive species are a threat to this habitat, eg. common sea-buckthorn (Hippophae rhamnoides) - which is very invasive and quickly spreads, shading out other plants. It also fixes nitrogen in the soil, which encourages other invasive species like Nettle (Urtica dioica) and Elder.

References

http://www.ni-environment.gov.uk/coastalsanddune.pdf