A detailed early postglacial (Flandrian) pollen diagram from Cwm Idwal, North Wales.

Abstract

Palynological investigation of lacustrine sediments in Llyn Idwal, in the uplands of Snowdonia, North Wales, has shown that pollen assemblages predating those at the base of Godwin's (1955) pollen diagram are recorded. These earlier pollen assemblages do not, however, indicate a revision of the Loch Lomond Readvance age of the last glaciers to occupy the cwm, Arctic-alpine flora presently growing on the cliffs of Cwm Idwal colonized the catchment as pioneer communities in the earliest postglacial, immediately following ice decay, but appear to have been driven to their present niches very early in the postglacial. Their subsequent reappearance is explained by natural or anthropogenically induced instability in local woodland, or perhaps by increased erosion and stream How affecting pollen transport from cliffs. Evidence is presented of a brief period of arid climate during the expansion of Juniperus, at around 10000 BP.