LATE-GLACIAL AND EARLY HOLOCENE VEGETATION OF SNOWDONIA

Detailed pollen and lithostratigraphic analyses of lake deposits at Cl ogwyngarreg provide a comprehensive record of vegetational and environ mental change in the lowlands of Snowdonia, north Wales during the lat e-glacial and early Holocene. A radiocarbon determination suggests tha t the lowlands were ice free by at least c. 13 500 sp, and that by tha t time open habitat herbaceous taxa, including abundant Rumex spp. wer e colonizing the recently deglaciated ground. The initial pioneer gras sland communities were gradually invaded by Juniperus and Betula, but the development of birch woodland was limited. An interstadial episode , the late-glacial Interstadial (Windermere Interstadial) is recognize d in the sequence of plant succession that culminated in the establish ment of juniper. A significant decline in Juniperus pollen frequencies and an increase in Gramineae, in the absence of an expansion in birch woodland, suggests that environmental conditions in the mid- to late- late-glacial Interstadial were less favourable to juniper than those o f the early-middle Interstadial. Towards the top of the Interstadial o rganic sequence fluctuations in the Juniperus pollen curve, coupled wi th high Isoetes spore values and the deposition of a stone horizon, su ggest local instability and re-working prior to the deposition of Loch Lomond (Younger Dryas) Stadial minerogenic sediments. By c. 11000 sp widespread solifluction and increasingly severe environmental conditio ns led to a breakup of existing plant communities and a proliferation of open habitat and disturbed ground taxa. During the Loch Lomond (You nger Dryas) Stadial, glaciers reoccupied the higher cwms of Snowdonia. Climatic amelioration, marking the Holocene at c. 10000 yr sp, was ch aracterized by a rapid expansion of Juniperus at Clogwyngarreg and evi dence for early Holocene woodland development is presented.