What is peat?

All peatlands, including bogs, develop in waterlogged conditions where dead plants decay slowly because of a lack of oxygen. The result of this in-situ accumulation of organic matter is peat. The rate of decay is so slow that the dead plant remains can resemble the living material even after several thousand years.

The term peatland refers to any wetland which contains peat, whether or not the natural vegetation and hence the processes of a peat-forming system still survive on the site. A mire is a wetland which supports at least some vegetation that is normally peat-forming. In some cases, the terms mire and peatland are synonymous, but when all trace of peat-forming vegetation has been lost, a peatland is no longer a mire. Equally, there are some mires where, despite the presence of species which are normally peat-forming, special circumstances have prevented the accumulation of peat.

In their natural state, peatlands, or more accurately mires, support distinctive assemblages of plants and other wildlife, including many species which depend on mire ecosystems for the major part of their natural distribution. Much of the natural heritage interest is derived from systems which are capable of accumulating peat. Peat accumulates largely because the decay of plant material is inhibited by waterlogging. Conditions which favour the development of a vegetation which is normally peat-forming vary widely in Britain, thereby giving rise to different kinds of mire. Here, a distinction between fens and bogs is important.

Fen systems are fed by direct precipitation and by water passing through the underlying mineral subsoil, sediments and rock, or by water which drains from the surrounding catchment as surface runoff or as lateral seepage. Thus, for example, fens may occur at the margins of lakes, on river flood plains and where there are springs or seepages. Fen systems may vary from base-rich to base-poor depending upon the soluble cations available from the surrounding and underlying geology, particularly calcium and magnesium. They may also vary from nutrient-rich to nutrient-poor depending on the levels of phosphorus and nitrogen available in solution. Not all fens are peat-forming, particularly where rates of water flow and/or high solute concentrations result in rapid breakdown of organic matter. Some fens may also be the ecological precursors of bog systems. Under appropriate management, usually involving intensive drainage, fen soils can support productive agricultural systems. Extensive tracts of fenland in Britain, indeed throughout Europe, have been drained for this purpose.

Bogs are found where there is no contact with the groundwater and the only source of water is rainfall. Only a few plants, such as the Sphagnum bog mosses, can cope with the extreme sterile and highly acidic conditions.

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