Coastal Ecosystems
Sand Dunes
There are four key conditions that sand dunes need to form and grow.
There are four key conditions that sand dunes need to form and grow.
- A good supply of sand
- Prevailing onshore winds
- Shallow offshore zone with a large gentle beach exposed at low tide
- A large backshore area to accumulate dunes
Ecosystem Succession on Sand Dunes
Embryo dunes
The first dunes or ‘embryo dunes’ begin as small piles of wind blown sand trapped by grasses such as sand couch and marram. Plants colonise initially by seed and then through their rhizomes thus stabilising the sand. This fresh sand has a high proportion of ground up, lime rich shells.
Yellow dunes
Behind these are the fore dunes or ‘yellow dunes’, which are much higher and more stable because of the marram grass. As the wind covers the plants in new layers of sand, the marram grass simply grows up through it, sending out a second root system just below the surface. As the sand keeps building up, the marram keeps growing, sending out new root systems thus stabilising the whole structure.
Grey dunes
A little further inland are the ‘grey dunes’ where the sand becomes carpeted by mosses and lichens, their colour giving the dunes their name. Here the marram gradually disappears to be replaced by plants adapted to the more stable soils. The seashell component of sand make it slightly alkaline but over time the calcium carbonate from the shells leaches out leaving the sand more acidic. This process leads to the development of heathland, and it is in these fixed dunes where the majority of plants and animals are found.
Dune Slacks
Between the dunes there are dips called dune slacks. These flood after heavy rain, so wetland species like creeping willow and sedge grow in the slacks.
Embryo dunes
The first dunes or ‘embryo dunes’ begin as small piles of wind blown sand trapped by grasses such as sand couch and marram. Plants colonise initially by seed and then through their rhizomes thus stabilising the sand. This fresh sand has a high proportion of ground up, lime rich shells.
Yellow dunes
Behind these are the fore dunes or ‘yellow dunes’, which are much higher and more stable because of the marram grass. As the wind covers the plants in new layers of sand, the marram grass simply grows up through it, sending out a second root system just below the surface. As the sand keeps building up, the marram keeps growing, sending out new root systems thus stabilising the whole structure.
Grey dunes
A little further inland are the ‘grey dunes’ where the sand becomes carpeted by mosses and lichens, their colour giving the dunes their name. Here the marram gradually disappears to be replaced by plants adapted to the more stable soils. The seashell component of sand make it slightly alkaline but over time the calcium carbonate from the shells leaches out leaving the sand more acidic. This process leads to the development of heathland, and it is in these fixed dunes where the majority of plants and animals are found.
Dune Slacks
Between the dunes there are dips called dune slacks. These flood after heavy rain, so wetland species like creeping willow and sedge grow in the slacks.
Human Interaction with Sand Dunes
- Sand dunes are picturesque locations and as such are popular with tourists. Human activity, however, can damage the dunes by exposing the sand causing erosion. The feet of tourists trample down vegetation and erode the fragile dune soil. Other human activities like quad biking and 4x4 off roading can cause massive damage to the dunes.
- Now sand dunes are often managed to protect them and prevent erosion. Dunes on nature reserves will often have area fenced off to prevent access. Paths through the dunes are constructed with matting or in the form of boardwalks, these further prevent erosion from trampling.