Soft engineering techniques can be used to stabilize coastal areas and reduce erosion. Planting vegetation on coastal dunes traps and binds sand to prevent it from blowing away. Mangrove trees have roots that anchor in soil and protect against erosion. Beach nourishment involves adding large amounts of sand to eroded beaches, which is carried further down the coast by longshore drift. Coral reefs reduce wave energy and protect beaches by absorbing wave energy before it reaches the shore.