Topogenous peat development and late- Flandrian vegetation history at a site in upland South Wales

Three radiocarbon-dated pollen diagrams were made from progressively shallower depths on a transect through an upland stream-valley bog in South Wales. The peat ranges in age from approximately 4000 to 2500 cal. BP. Comparison of the pollen diagrams shows that local vegetational changes can be distinguished and different histories emerge at sites only tens of metres apart. Despite this, general trends can be distinguished. There is evidence of increased soil moisture and the growth of willows as organic material began to accumulate in the central part of the valley around 4000 cal. BP. Reduction of trees accompanied true blanket peat inception, perhaps around 3800 cal. BP. At the margin, however, tree reduction preceded the peat formation which began at least 1000 years later. The process was here accompanied by podsolization. Some woodland remained near the site until the end of the Bronze Age. There was an increase of soil moisture during, or close to the end of, Romano-British times. An increase of healthy ground cover occurred around 350-700 cal. BP but there was a reversion to more grassy conditions in relatively recent times. There is little evidence of human impacts. The vegetational and soil changes at the site appear to be attributable principally to climatic deterioration or local hydrological changes.