Vegetation

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Stages of Succession

You need to be able to describe and explain the development of a special ecosystem - sand dunes.

You should also be able to describe and explain the adaptations that plant species have made to cope with the environment.

Sand dunes

At the pioneer stage, seeds are blown in by the wind or washed in by the sea. The rooting conditions are poor due to drought, strong winds, salty sea-water immersion and alkali conditions created by sea shells. The wind moves sand in the dunes and this allows rainwater to soak through rapidly.

At the building stage, plants trap sand and grow with it, binding the sand together with their roots. The humus created by decaying pioneer plants creates more fertile growing conditions, and the soil becomes less alkaline as pioneer plants grow and trap rainwater. Less hardy plants can now grow and start to shade out the pioneers. As plants colonise the dunes, the sand disappears and the dunes change colour - from yellow to grey.

At the climax stage, taller plants (such as trees) and more complex plant species (like moorland heathers) can now grow. Plants from earlier stages die out because of competition for light and water. When the water table reaches or nearly reaches the surface, dune slacks can occur. Plants which are specially adapted to be water-tolerant grow here.

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