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Just shorewards of the embryo dunes are the older and slightly higher dunes called foredunes. Sometimes they are referred to as yellow dunes because of the high proportion (c. 20%) of visible sand. Here marram grass begins to dominate. Spreading like the couch with horizontal stems called rhizomes, it too can survive burial by the accumulating sands. Indeed growth of the marram grass is stimulated by burial by sand. In common with the sea couch grass, it is also tolerant of salt.
Marram grass is adapted to the dry conditions by having leaves which are tightly rolled, protecting the stomata on the base of the leaf from loss of moisture. The leaf, once unrolled, can be seen to have a downy appearance which is the result of having fine hairs. These, and the grooves running lengthways along the leaf inside which the stomata are located, also help to reduce moisture loss through transpiration. Marram can align itself with the prevailing wind and has a shiny surface to the outside of the rolled-up leaf both of these serve to further reduce moisture loss. The marram grass has long rhizomes which grow laterally and vertically. The long tap roots reach groundwater deep below the surface. These stems also help to stabilise the sand allowing other species to colonise the dunes.
Follow the links in the diagram below to explore the dunes.
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