An accumulation of blown sand found on the coast and in inland desert areas. Coastal dunes are formed by inshore winds that carry sand particles and deposit them on various obstacles in their path, such as pieces of seaweed. In regions that are relatively undisturbed by the tides, seeds of xerophytic plants germinate and establish a pioneer community termed a psammosere. The plants tolerate abrasion by blown sand, high winds, high temperatures in the day, and some salt from sea spray. Sand twitch (Agropyron junceiforme) helps to stabilize the dune with its extensive network of rhizomes. It is also tolerant to limited immersion in sea water. Marram grass (Ammophila arenaria) then becomes established, although in some cases it may itself be the pioneer plant. Like sand twitch, marram grass has a network of rhizomes that stablizes the dune but it is intolerant to immersion in sea water. The landward slopes of the dunes are more sheltered and less steep than the seaward slopes and other plants grow including lyme grass (Elymus arenarius), sea holly (Eryngium maritimum), etc. A dune system is established, the innermost series being stable and termed fixed dunes. Behind these, dune pasture occurs with typical dune plants together with species commonly found in pasture. See also xerophyte , xerosere. |
