Sand dune ecology

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Sand dune ecology describes the biological and physico-chemical interactions that are a characteristic of sand dunes.

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Sand dune systems are excellent places for biodiversity, partly because they are not very productive for agriculture, and partly because disturbed, stressful, and stable habitats are present in proximity to each other. Many of them are protected as nature reserves, and some are parts of larger conservation areas, incorporating other coastal habitats like salt marshes, mud flats, grasslands, scrub, and woodland.

Plant habitat

Sand dunes provide a range of habitats for a range of unusual, interesting and characteristic plants that can cope with disturbed habitats. In the UK these may include restharrow Ononis repens , sand spurge Euphorbia arenaria and ragwort Senecio vulgaris - such plants are termed ruderals.

Other very specialised plants are adapted to the accretion of sand, surviving the continual burial of their shoots by sending up very rapid vertical growth. Marram grass, Ammophila arenaria specialises in this, and is largely responsible for the formation and stabilisation of many dunes by binding sand grains together. The sand couch-grass Elytrigia juncea also performs this function on the seaward edge of the dunes, and is responsible, with some other pioneers like the sea rocket Cakile maritima , for initiating the process of dune building by trapping wind blown sand.

In accreting situations small mounds of vegetation or tide-washed debris form and tend to enlarge as the wind-speed drops in the lee of the mound, allowing blowing sand (picked up from the off-shore banks) to fall out of the air stream. The pioneering plants are physiologically adapted to withstand the problems of high salt contents in the air and soil, and are good examples of stress tolerators, as well as having some ruderal characteristics.

Inland side

On the inland side of dunes conditions are less severe, and links type grasslands develop with a range of grassland herbs which benefit from the reasonable nutrient status and moderately high pH of the more stable soils, especially when enough humus has accumulated in stabilised soils for water retention to be improved. Species like red fescue and lady's bedstraw are adapted to compete with each other - for nutrients, growing space and light, and are known as CSR plants - i.e. having features of Competitors, Stress tolerators and Ruderals in more or less equal proportions.

There may also be areas in old blow-outs where groundwater is near the surface, and often rises to cause flooding in the winter. Frequent, but intermittent waterlogging of the roots requires adaptations to stress, so the proportions of stress tolerators are increased here.

In nutrient-rich water, however there are some plants with very competitive strategies, like the reed ( Phragmites australis ). This is an example of a plant which makes rapid growth and suppresses other species by monopolising root and shoot space and shading out the opposition. Even its own seedlings are prevented from establishing within the existing population, but seeds are blown for long distances in copious quantities to start new colonies, whilst mature populations extend by rapid vegetative growth of lateral underground shoots - rhizomes.

See also

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<i>Ammophila</i> (plant) Genus of flowering plants in the grass family Poaceae

Ammophila is a genus of flowering plants consisting of two or three very similar species of grasses. The common names for these grasses include marram grass, bent grass, and beachgrass. These grasses are found almost exclusively on the first line of coastal sand dunes. Their extensive systems of creeping underground stems or rhizomes allow them to thrive under conditions of shifting sands and high winds, and to help stabilize and prevent coastal erosion. Ammophila species are native to the coasts of the North Atlantic Ocean where they are usually the dominant species on sand dunes. Their native range includes few inland regions, with the Great Lakes of North America being the main exception. The genus name Ammophila originates from the Greek words ἄμμος (ámmos), meaning "sand", and φίλος (philos), meaning "friend".

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Ammophila breviligulata is a species of grass native to eastern North America, where it grows on sand dunes along the Atlantic Ocean and Great Lakes coasts. Beachgrass thrives under conditions of shifting sand, sand burial, and high winds; it is a dune-building grass that builds the first line of sand dunes along the coast. Beachgrass is less vigorous in stabilized sand, and is only infrequently found further inland than the coastal foredunes. On the Atlantic coastline of North America, Ammophila breviligulata has been observed as far south as North Carolina, and is often planted in dune restoration projects. Ammophila breviligulata was introduced to the Pacific coast of North America in the 1930s. It is proving to be invasive, and is increasingly important to coastal ecology and development in Oregon, Washington, and British Columbia.

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