Man and mire: a long and wet relationship

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Abstract
Several different types of mire, that is peat-forming ecosystem, contain in their stratigraphic and pollen record evidence of human activity. Often this coincides with either the commencement of peat formation or a major change in the type of peat being formed. Some mires can therefore be regarded as man-made habitats. Examples are discussed which include valley mires in southern Spain and in England, a schwingmoor in central Wales, and the blanket mires of upland and western Britain. All of these show majorchanges in their stratigraphy at a time when human influence, as exhibited in the pollen record, is particularly strong. The effects of man on valley mire and blanket mire initiation is mainly a consequence of hydrological change; deforestation increases the frequency of soil saturation and the quantity of run-off water. The result is impaired decomposition and peat accumulation. Downwash of silts and charcoal can also enhance this effect in valley mires, as can podsolization in blanket mires. A further effect of deforestation, the nutrient enrichment of drainage waters, is shown to be of particular importance in the initiation of a floating raft of acquatics at the schwingmoor, Llyn Mire, and hence led to the development of a raft of bog vegetation over a former lake. On the basis of these examples the question of just how widespread is man's influence on mire development is discussed.