TOPOGENOUS PEAT DEVELOPMENT AND LATE-FLANDRIAN VEGETATION HISTORY AT A SITE IN UPLAND SOUTH WALES

Three radiocarbon-dated pollen diagrams were made from progressively s hallower depths on a transect through an upland stream-valley bog in S outh Wales. The pear 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 o nly tens of metres apart. Despite this, general trends can be distingu ished. 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 b lanket peat inception, perhaps around 3800 cal. BP. At the margin, how ever, tree reduction preceded the peat formation which began at least 1000 years later. The process was here accompanied by podsolization. S ome woodland remained near the site until the end of the Bronze Age. T here was an increase of soil moisture during, or close to the end of, Romano-British times. An increase of healthy ground cover occurred aro und 350-700 cal. BP but there was a reversion to more grassy condition s in relatively recent times. There is little evidence of human impact s. The vegetational and soil changes at the site appear to be attribut able principally to climatic deterioration or local hydrological chang es.