The grey dunes are much more stable and mosses and lichens fill the few remaining spaces between plants so that vegetation cover may reach 100%. Marram grass becomes less common and appears now in isolated patches. Red fescue, sand sedge, sea spurge begin to dominate. Small shrubs (brambles, gorse, buckthorn) appear for the first time. Environmental conditions 50-100 metres from the sea are much more friendly. There is shelter from the harshest winds, humus is beginning to darken the surface layers and a true soil begins to form. Soil pH is increasingly acid and heathers may take advantage of the acid conditions. Water content is still low and plants have to search for water with their spreading root systems. These large dunes are commonly 10 metres in height and wider than those dunes nearer the shore.