Postglacial vegetational dynamics in lowland North Wales
This study elucidates the Postglacial vegetational history of lowland lake sites in Gwynedd using detailed palynological work integrated with radiocarbon dating, loss-on-ignition, chemical, charcoal, and X-ray diffraction analyses. An early Postglacial phase of Juniperus-Betula scrub was succeeded by open Betula-Corylus woodland at Llyn Cororion, a kettlehole site on the Arfon Platform (SH597688). Ouercus and tilmus were established by 8600 BP and Pinus dominated locally at 8425 BP. A subsequent water level rise and fire disturbance encouraged the spread of Alnus. Tilia was established by 5650 BP. Progressive deforestation began in the Late Bronze Age with increased fire use and spread of grassland; cereals are first recorded at 2900 BP. There is evidence that Llyn Cororion was used for Cannabis retting during Mediaeval times. Postglacial vegetation at Llyn Hendref (SH398765), an exposed lake basin on Anglesey, was dominated by CoryJ.us and Alnus; mixed, open oak woodland occurred away from the lake basin but Tili p and Pinus were never abundant. In the late Postglacial there was increased fire disturbance resulting in effective soil erosion and acceleration of mire development. Mire encroachment increased around 8700 BP resulting in lake shallowing and increased sediment erosion and redistribution. Site comparison with published work (Melynllyn and Nant Ffrancon) shows that there were variations in vegetational development within North Wales. Radiocarbon dating shows that similar vegetational events were time transgressive determined by migration rates, soil conditions, competition, hydrology and altitude.