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A cyclic change in the vegetation that takes place on a developing raised bog. A pool of water on the peat is invaded by Sphagnum mosses and a low hummock is built up. Other plants, such as Calluna vulgaris (ling) and Erica tetralix (crossleaved heath), then establish themselves. When the ling dies the hummock is easily eroded and reduced to a water-filled hollow surrounded by other hummocks in various stages. The cycle can then be repeated. Similar cycles occur in grassland, and in the tundra where frost hummocks of peat are formed by frost action and subsequently eroded.
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