Fire and Flood at Holme Moss: Erosion Processes in an Upland Blanket Mire

(1) Holme Moss is an upland blanket mire in the southern Pennines that is unusual for the variety and severity of its peat erosion. (2) The results of microfossil and macrofossil analyses of peat formed in the last 1200 years at eleven sites on Holme Moss are presented. Quantitative estimates of the frequency of leaves of Sphagnum and Racomitrium lanuginosum in the various peat cores are compared, with the aid of a dating template based on the pollen diagrams, and used to infer conditions on the mire surface at different times in the past. (3) The pollen-stratigraphic data indicate that peat erosion has been active on Holme Moss for four to five centuries, and has involved several distinct episodes. The current mire vegetation has developed subsequent to these episodes of erosion, and represents the effects of air pollution and intense sheep grazing superimposed on an already eroded ecosystem. (4) The main peat gullies on Holme Moss probably originated following clearance of forest from the surrounding hillslopes in the eleventh century. Well-defined soakways or flowlines formed on the mire surface, and subsequently developed into open drainage channels. However, certain of the peat gullies were probably not incised until the eighteenth or nineteenth century; and considerable areas of Holme Moss were still unaffected by gullying when renewed Sphagnum growth in the sixteenth century led to the formation of a Sphagnum-dominated mire surface over much of the western half of the moss. (5) Concentrations of burnt plant material at certain levels in the peat cores indicate that the drier eastern half of Holme Moss was severely burnt at least once in the eighteenth century; much peat may have been lost as a result of the fire and subsequent erosion. (6) A freak cloudburst is recorded for the Holme Moss area in July 1777. This cloudburst may have caused extensive damage to the margins of the peat blanket, and accentuated existing erosion features. (7) It is concluded that much of the peat erosion currently visible on Holme Moss has been produced by exceptional events, either natural or man-made; and that analysis of current environmental stresses at Holme Moss offers few clues to the causes of peat erosion.