Peat Bogs

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Peat bogs occur at the mountain and sub Alpine levels. These damp areas have originated in the lakes established in the glacial hollows, as on the Plateau de Limon and Chastel sur Murat.

The largest of them can reach several hectares. Smaller ones are scattered on the slopes of Prat de Bouc, Peyre Arse and Puy Violent. These resulted from poor drainage, either from rainwater or a spring. They are gradually filled by vegetation growing towards the centre and in depth. All are characterised by an acid and slightly mineral water and the presence of sphagnum moss.

Sphagnum moss can hold almost thirty times its own weight in water. Originally, the roots of plants grew towards the water source and the moss then grew on this network of roots.
 Other species of plants then grew between the mosses. The peat bogs differ from the plains marshes by the accumulation of progressively decomposing vegetation. The temperature at the base of the bog and the acidity of the water slows the decomposition of the plant matter, which then builds up the depth of peat and reduces the moisture. This can be in the region of 3-5cm per century.

The peat bogs shelter several plant species that are relics of the glaciers. The best known are the cotton grass, bog rosemary and cranberry which grow from the spongy moss carpet. Other plants are even more original in their specialisation to life in acid areas with little nutrition. These are the carnivorous plants. The round-leaved sundew feeds on flies, midges or small dragonflies. It holds its prey prisoner by hairs soaked with a gluey substance, before digesting them. The butterwort counteracts the shortage of nitrogen in the damp soil by trapping its prey on its fleshy leaves. The more delicate bladderwort has specialised organs for digesting minute aquatic organisms.

 Puy Peyre Arse

Classic Geology in Auvergne by Peter Cattermole ISBN 1-903544-05-x available from Blackwells