A succession to ombrotrophic bog in the Gwent Levels, and its demise: a Welsh parallel to the peats of the Somerset Levels

SUMMARY Vegetational history in the period 7000–3000 years ago is described at two adjacent locations in the intertidal zone of the Gwent Levels. The evidence, which bears mainly on the succession of peat-forming communities, is taken from stratigraphy, lithology, pollen, and plant macro-remains. The sequences are dated by means of calibrated radiocarbon dates. At about 6900 B. P. (before present), Phragmites swamp was established on estuarine clay, probably succeeding salt marsh at the higher of the two sites. By about 6700 B. P., after a pioneer phase involving colonization by willows, alder carr was coming into existence. This persisted as a stable community for some 600 years. During its existence there was a minor marine incursion which had little overall effect. There was then a retrogressive succession to reedswamp, probably brought about by an increase of water level, possibly related to changes of tide levels in the Bristol Channel. Phragmites was succeeded by Cladium mariscus (L.) Pohl. as the water became shallower. This was in turn succeeded by a drier fen-meadow or fen-grassland but no recolonization by willows or alder ensued. The lack of renewed carr development may have been due to depletion of mineral nutrients. The reedswamp and fen stages lasted for some 300 years overall. The role of oak remains problematic and requires further investigation. The fen gave way to ombrotrophic bog at about 5750 B. P. Via a‘transition bog’stage . The raised bog, which was the culmination of the succession, was annihilated by renewed deposition of estuarine sediments at about 3400 B. p. The discussion sets the succession on the Gwent Levels in the context of general considerations about postglacial hydroseres and makes a comparison with the history of the Somerset Levels. A Neolithic farming phase is compared with those previously described from the north-east of Ireland (Pilcher et al., 1971). The Goldcliff phase has three stages of comparable age and duration, but differs in having cereal type pollen in the second stage following the elm decline rather than the first.