Sand dunes, the piles of sand that form near the shore, go through various stages of succession. With each new succession stage, the sand dunes gradually move away from the sea and support different varieties of plant and animal life. Eventually, sand dunes may develop into woodlands.
Dune Building Stage
When local wind speeds drop, the sand being carried by the wind also drops into small piles. These deposits of sand grow into new sand dunes. If wind speeds remain slow, the sand dunes will stay where they are. If wind speeds increase, the dunes will move inland.
During the pioneer stage, small plants such as sand couch grass and lyme grass form on the dunes. The high salt tolerance of these grasses allows them to thrive near seawater. When sand deposits increase, however, the large volumes of sand smother these plants, and marram grass grows in their place. Pioneer stage dunes, as well as future dune stages, host various migrating insects, particularly butterflies and moths.
Yellow (White) Stage
The yellow, or white stage of succession is characterised by marram grass, which has a deep root system that binds and stabilises the dunes. Other plants, such as sea splurge and Portland splurge, populate the hotter and drier areas of dunes during this stage. These plants have waxy leaves that enable them to survive in dry areas, and taste unpleasant to the rabbits found in these dunes. From this stage, dunes will progress to the calcareous or acidic grey stage.
Calcareous Grey Stage
The calcareous grey stage is marked by lichens, moss and continuous plant growth all over the surface of the dunes. While this vegetation can retain some water, dunes are still generally dry during this stage, and mosses and lichens tend to become dry and hard in the summer months. Sand is no longer deposited on the dunes, and marram grass dies out as a result. Flowers and herbs, such as orchids, primrose and wild thyme, begin to grow on dunes in this stage of succession. The next stage of dune succession may be the acidic stage or the dune scrub stage.
Acidic Grey Stage
The acidic grey stage occurs when rainwater leaches out nutrients from the dunes, causing them to develop acidic soil. During this stage, plants characteristic of acidic grasslands, such as heather, gorse and bracken, develop on the dunes.
Dune Scrub Stage
By the dune scrub stage, sand has developed into poor, sandy soil. During this stage, bushes, particularly the creeping willow, form on the tops and hollows of the dunes. Orchids and grasses are also commonly seen on dunes during this stage, as well as bright red leaf beetles.
Conifer Plantation Stage
In this final stage, dunes can support conifers such as the Corsican Pine, which has a high salt tolerance. These trees may be planted by humans, but eventually grow there on their own.