Late-glacial and early Holocene vegetation of Snowdonia.

Detailed pollen and lithostratigraphic analyses of lake deposits at Clogwyngarreg provide a comprehensive record of vegetational and environmental change in the lowlands of Snowdonia, north Wales during the late-glacial and early Holocene. A radiocarbon determination suggests that the low lands were ice free by at least c. 13 500 BP, and that by that time open habitat herbaceous taxa, including abundant Rumex spp. were colonizing the recently deglaciated ground. The initial pioneer grassland 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 recognized in the sequence of plant succession that culminated in the establishment 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 of the early-middle lnterstadial. Towards the top of the Interstadial organic sequence fluctuations in the Juniperus pollen curve, coupled with Isoetes spore values and the deposition of a stone horizon, suggest local instability and re-working prior to the deposition of Loch Lomond (Younger Dryas) Stadial minerogenic sediments. By c. 11000 BP widespread solifluction and increasingly severe environmental conditions led to a breakup of existing plant communities and a proliferation of open habitat and disturbed ground taxa. During the Loch Lomond (Younger Dryas) Stadial, glaciers reoccupied the higher cwms of Snowdonia. Climatic amelioration, marking the Holocene at c. 10000 yr BP, was characterized by a rapid expansion of Juniperus at Clogwyngarreg and evidence for early Holocene woodland development is presented. [ABSTRACT FROM AUTHOR]