switch

The sand dune system at Chrystalls Beach, New Zealand comprises front dune, dune hollow and rear dune areas. On the front dunes are two communities: one on the seaward face of the dunes, and another on the landward face. Most of the dune hollow is occupied by a series of grassland communities, but there are areas of a distinctive cushion community, still largely native in its species composition. It is suggested that the cushion community is maintained against invasion by a switch, possibly involving sand grain size, soil organic content, water supply, wind and magnesium:calcium ratio.