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Marram Grass - Ammophila arenaria

See also: sand dune

Marram is an extremely tough and highly specialised perennial grass that colonises and fixes the shifting sands of coastal dune systems.

Appearance

Marram grass is blueish green in colour, growing in dense clumps to a height of between 50 - 120 centimetres. Each leaf is rigid and pointed, (not pleasant to walk through in shorts by any means) and able to roll in on itself to protect its stomata and prevent water loss. Its flowers look like ears of corn, and can be seen from June to August.

Where can I find it?

Marram grass can almost always be found on the upper shore of sandy areas, above the high water mark (the highest line of seaweed and litter thrown up by the sea). It grows best on the dynamic shifting sands of embryo dunes, sand dunes that are not yet fixed in position, constantly moving and re-forming along the shoreline. Marram grass helps to stabilise these baby dunes by causing a dead zone around its base - this being an area where the wind doesn't blow, thus trapping sand and helping a dune to grow higher. Marram grass is also found on fixed dunes, the next stage in the dune system, but gradually loses its dominance giving way to species such as couch grasses, spurges, sea buckthorn and tamarisk.

Specialised?

Marram is one of the most prevalent and successful colonisers of dune systems throughout Europe and America. Introduced to New Zealand and Tasmania as a dune stabilising species in the 1930s and 1960s, it is now seen as an invasive species capable of wiping out native grasses and fundamentally changing the nature of southern hemisphere dune systems.

But what makes it so successful?
Marram is capable of growing in one of the harshest habitats on the planet. Not only can it cope with being covered in salt, constantly berated by the wind and any goodness reaching it being leached from its roots through the highly porous sandy soil, but has to cope with being frequently buried and the sides of the dunes it colonises collapsing due to wind erosion and encroachment by the sea.

To most plants, it would be folly to even attempt to live in these conditions, but all this harsh treatment only causes marram grass to grow more vigourously. It produces vast ammounts of densely spreading rhizomes, a root system capable of producing a new plant almost every two inches of its length. These roots anchor the plant in the sand, but also help it spread to new territory. If a two inch fragment of the root is snapped off, then it contains everything it needs to start a new clump of marram wherever it lands.

The rhizomes not only grow horizontally, but vertically as well, meaning that when marram grass is buried, this actively encourages it to grow upwards and outwards. This extra growth spurt only helps to further anchor the plant, trap more sand and increase the 'fixed' nature of the sand dune. Marram plants are never totally anchored in one place however, and gradually move in the direction of the prevailing wind, into new sand that builds up in the lee of the original clump.

As already mentioned, the leaves are capable of rolling up in particularly arid, sand blasted or salty conditions, protecting the stomata, (the water releasing, breath holes of a plant) and keeping them in reletively humid and stable conditions. The leaves are bluey green in colour which helps to lessen the effects of evapotranspiration and helps the plant to retain water by reflecting sunlight.

Pretty unstoppable then...

Marram grass may be particularly well adapted to living and growing in a harsh environment, but it has virtually no defence against the most common threat to nature - people.

Dune systems are constantly under threat from erosion, normally more due to people sliding down dunes and destabilising them, or tramping across plantations of marram grass and destroying it, than from natural encroahment by the sea. Marram cannot cope with being heavily trampled and this often leads to 'blow outs' where sand dunes totally collapse. If dunes are being destroyed faster than they are created (as often starts to happen in areas where they are only used for recreation and not protected), then many important and specialised species will be lost.

I doubt that marram will be one of them however.


Sources:
The Natural History of Britain's Coasts - Soothill and Thomas - 1988 - New Orchard Press
http://64.233.183.104/search?q=cache:iPaZH3HS7I8J:www.parks.tas.gov.au/notesheets/threats/MarramGrass.pdf+marram+grass&hl=en

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