Coastal sand dunes develop from the accumulation of wind-blown sand (sediment between 0.2 to 2mm). Between periods of high tides, sandy shores dry out & the sand grains are blown inland, above the high water mark & are trapped by dune-building grasses to form mounds of sand that line the coast.
- Site: Onshore wind, nutrient poor, water deficient
- Sand: Dried, 0.2-2mm
- Main species: Marram grass
- UK: 55,998 ha
- NI: 3,000 ha
- Coastal sand dunes are diverse habitats that develop when there is an adequate supply of sand & onshore wind. During high tides, the sand that is deposited on a large beach plain dries, which makes it easily transported. A breeze of just over 4.5m/s can move dry sand landwards where it accumulates to form the classic mounds of sand (NIEA, 2005).
- The high structural diversity of sand dunes & their characteristic appearance is a result of the plant communities, which trap the sand.
- The vegetation depends on the length of time since the sand was deposited & local conditions. Pioneer species such as sea rocket Cakile maritima & sand couch grass Elytrigia juncea colonise areas of windblown sand.
- Marram grass Ammophila arenaria, the key species in UK dune formation, dominates foredunes (or yellow dunes) & mobile dune communities. Its deep vertical root system ensures that it can withstand poor water availablility & becoming buried by the rapidly accumulating sand.
- Over time the deposited sand forms ridges which may break up, forming hills (dunes) & hollows (dune-slacks). Less generalist plants such as gorse Ulex europeaus, blackthorn Prunus spinosa & the invasive sea buckthorn Elaeagnus rhamnoides, can colonise until dune grassland becomes scrub, then woodland (‘climax community’).
- The typical stages in sand dune succession are: strandline to mobile (yellow) & fixed (grey) dunes, grassland (dominated by Red fescue Festuca rubra), heath, scrub & finally woodland. Grazing & trampling can prevent or reverse this succession (NIEA, 2005).
Current Status in UK & Northern Ireland
- By combining estimates from the Sand Dune Survey of Great Britain (1993-1995) & the Sand Dune Vegetation Survey of Scotland, there are approximately 55,998 ha of sand dunes in the UK (England: 11,897 ha, Wales: 8101ha, Scotland: 33,000 ha).
- There is approximately 3000 ha of dunes in Northern Ireland, but the area of sand dune vegetation is estimated between 1300 & 1500 ha (EHS, unpublished).
- In NI the largest dune systems are along the north & south-east coasts.
- Magilligan is one of the largest calcareous dune systems in the UK, with fixed dunes & well-developed dune slack communities. Other large areas include White Park Bay, Bann Estuary & Portstewart.
- The youngest sand dune systems in NI occur at Magilligan & the mouth of the Bann Estuary.
- Coastal sand dunes are threatened by reduction in water tables by extraction of water and/or drainage of adjacent land, which can result in the loss of specialist slack plants & invasion by coarse vegetation & scrub. Sand dunes are also threatened by both over & under-grazing, pressures from human activities such as trampling, vehicle damage (e.g. motorcycles) & golf courses which are often established on sand dunes. Further problems include housing & industrial developments, waste disposal, sand removal & alien species.
- Grangemore Dunes [Bann Estuary ]
- Portstewart Strand & Dunes
- The Umbra
- White Park Bay