Kingdom: Plantae
Order: Poales
Family: Poaceae
Genus: Ammophila
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Species: A. arenaria
Species: A. breviligulata
From the Greek Ammos, meaning 'sand', and Philia, meaning 'affinity'. Common names for these plants include Marram Grass, Bent Grass, and Beachgrass.
Members of the genus Ammophilia do indeed have an affinity for sand. Their habitat is limited to sand dunes along the coast; they both prefer and help create a type of dune called the foredune, a comparatively steep dune paralleling the coast. They are native to Europe and North Africa (A. arenaria) and Eastern North America, including the Great Lakes (A. breviligulata). They were deemed so useful by the British that the "The Empire on which the sun never sets" introduced them to Africa, Australia, South America, and numerous islands around the world. Because of this marram grass is now often considered an invasive species, and many areas are undertaking the difficult task of eradicating it.
In its natural habitat, however, marram grass is an important and useful plant. Few plants can live on moving sand dunes, but marram grasses live best on the forefront of dunes, growing all the faster when they are buried by blowing sands. They tend to live on the dunes closest to the coast, and seem to be inhibited from growing in inland dunes which have higher levels of nutrients and microorganisms in the soil. Once marram grasses take root on the dunes they settle the sand with their extensive root systems, and once they die their remains provide nutrients for other plants that can then move into the area. They are the first settlers in a chain of events that can change a sand dune into a thriving prairie or woodland.
In addition, humans can use marram grass for making certain goods; in England the leaves of marram grass have been used since at least the 1500s to make woven mats, baskets, brushes, and thatch. In some cases the overharvesting of marram for these purposes became so severe that sand dunes started to migrate inland, burying productive farm land and villages. In 1695 the Scottish Parliament banned harvesting marram and other dune grasses. The roots were also used to make rope and mats, and the stems can be used to make paper, although apparently this last was not common. They also make acceptable fodder for cattle, and at least one source reports that the roots can be eaten by humans.
So why would you want to get rid of marram grass? Well, coastal ecosystems are greatly affected by dune structure. Marram grass can be a little too effective at building sand dunes; dunes with a population of marram grass can often reach from 3 to 8 meters in height, and can push closer to the coast than moving dunes. This effect can be exacerbated by waves cutting into the base of the dune, in effect making a 'cliff' of sand. This type of growth can prevent small animals (such as crabs) from migrating from the sea to the dunes.
Some birds, such as the Western Snowy Plover (California) and the Chatham Island oystercatcher (New Zealand) require wide stretches of open sand for nesting, and stable dunes pressing close to the coast force them to nest too near to the tideline, endangering their nests. The grass also provides cover for predators to sneak up on the birds, who would prefer to nest in open areas.
On top of this, marram grass can also push out native species of plants. While these plants may not be as effective at pinning down the dunes, they are still an important part of the local ecosystem, and replacing them changes the animal populations that hunt, feed, and live in them.