Now dunes are only little sand hills, formed by waves and wind and, where unstabilized, extremely vulnerable to these selfsame forces. Yet there are grasses, sedges in Europe and marram in the United States, which are the pioneers of this environment. They are astonishingly tolerant to high salinity, extreme glare, soils lacking humus, an uncertain and oscillating supply of water. Indeed they thrive on these conditions, and as the sand piles around the neck of the plants the roots extend below ground and the stems and leaves rise from the sand. The product is a dense mat of roots, which stabilize the dune below and the leaves that entrap sand and anchor it above ground level.