PALAEOECOLOGY OF <em>ALNUS</em> (ALDER): EARLY POST-GLACIAL RISE IN A VALLEY MIRE, NORTH-WEST WALES.

Data are presented in summary form in both percentage and influx radiocarbon-dated pollen diagrams from a site (MYG) in a valley mire near Moel y Gerddi, Ardudwy, 4 km north-east of Harlech, north-west Wales. Evidence indicates that this valley mire was dominated by alder (Alnus) carr soon after the inception of peat growth, which dates from 8700 B.P. These data confirm the notion of an early empirical limit of Alnus in north-west Wales (advanced in a previous paper) and, compared with other sites in Wales and the rest of Britain, indicate a very early rational limit here for Alnus (c. 8465 B.P.). Ideas on the migration route and on the spread of Alnus into Britain in the Post-glacial may need substantial revision in the light of this evidence for an earlier presence of Alnus in upland Ardudwy, north-west Wales, than yet known from lowland south-east England. Conceivably, Mesolithic activity might have facilitated the local establishment of Alnus; the evidence for this in upland Ardudwy is evaluated. [ABSTRACT FROM AUTHOR]