Title:
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Pollen analysis and radiocarbon dating of late glacial and early flandrian sediments in North Wales.
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Detailed pollen analyses, together with analyses of deteriorated
pollen and spores and lithological investigations, were carried out
at four sites along an east-west transect of the mountains of north
Wales. A total of twelve radiocarbon dates were obtained from
critical horizons at the four sites investigated. Two of the pollen
profiles (Clogwyngarreg in the west and Llyn Goddionduon in the east)
provide a detailed record of vegetational and environmental change in
the lowlands of north Wales during the Lateglacial (Late-Devensian
lateglacial) and early Flandrian periods, while two other profiles
(Cwm Cywion and Llyn Llydaw) provide a detailed record of early and
mid Flandrian (postglacial) vegetational and environmental history in
the uplands of north Wales. Radiocarbon dates from the base of the
Lateglacial profiles suggest that the Late-Devensian ice-sheet had
disappeared from the lowlands of north Wales by £ 13,500 B.P., and
that by that time open habitat herbaceous taxa, including abundant
Rumex sp. were colonizing the recently deglaciated ground. The initial
pioneer grassland communities were gradually invaded by juniper and
birch, but the development of birch scrub appears to have been sporadic,
and to have been generally more favoured in the eastern district. An
interstadial episode (the 'Lateglacial Interstadial') is recognized in
the sequence of plant succession that culminated in the establishment
of juniper and birch scrub. A decline in Juniperus pollen frequencies
and en increase in herb pollen valu9s (mainly grasses) at the western
site of Clogwyngarreg, and fluctuations in the curves for Junioerus
and Betula at the eastern site of Llyn Goddionduon suggest that
environmental conditions in the latter part of the interstadiil may
have been less favourable than those of the earlier/mid interstadial
period. By £ 11,000 B.P. widespread solifluction and increasingly
severe environmental conditions led to the break-up of existing plant
communities and the proliferation of open-habitat and disturbed ground
taxa. During this Stadial period (the 'Loch Lomond Stadial') glaciers
reoccupied the highland cwms of Snowdonia. Climatic amelioration at
the beginning of the Postglacial (Flandrian) was charactarized by a
rapid expansion in Juniperus at the low altitude sites, while a
pioneer grassland phase, in which Rumex species were prominent, predates
the arrival of Juniperus at the recently deglaciated high
altitude sites. Early Flandrian vegetational developments between
the uplands and the lowlands may have been time-transgressive, but the
available radiocarbon dates are inconclusive on this point. Local
variations in Flandrian woodland development are described and are
thought to reflect both environmental differences and compstitirin
factors. At one site (Llyn Llydaw) Flandrian woodland history is
traced up to the onset of deforestation in late Neolithic/early Bronze
age times.
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