A POST‐GLACIAL POLLEN SEQUENCE FROM LOCH A'MHUILINN, NORTH ARRAN: A RECORD OF VEGETATION HISTORY WITH SPECIAL REFERENCE TO THE HISTORY OF ENDEMIC SORBUS SPECIES

Abstract

SUMMARYA sequence of lake muds and fen peat deposits from Loch a'Mhuilinn, north Arran, contains evidence for the local vegetation history for parts of the Flandrian Interglacial. The main components of this history are as follows:Sedimentation occurred under open-water conditions during early Flandrian times. By around 5000 B.P., fen peat was accumulating, and during the 2nd millenium B.P., an unexplained reversion to open-water conditions occurred.The earliest recorded vegetation immediately predates the Corylus rise and is characterized by Betula-rich woodland with Juniperus and Salix being present in places. The Corylus rise, occurring at around 8600 B.P., marks the beginning of a period of Corylus-r'ich Betula woodland. Subsequent increases of Ulmus, Quercus, Pinus and Alnus pollen represent further forest development. Fluctuations in the composition of this mixed forest are recognized, as can a distinction between areas of Betula-Quercus, Corylus-v'ich and Alnus-rich. woodland.At around 5000 B.P., the vegetational development, previously representing broad regional changes, appears to respond to local processes. Fluctuations in the proportions of trees and Gramineae pollen may reflect vegetational disturbance, although sedimentation processes may be influencing the pollen deposition at this time. This period is followed by apparently greater woodland stability, with minor indications of human activity. By around 4000 B.P., early stages of Calluna-rich heath are apparent. The development of the heath vegetation is not recorded, but by the 2nd millenium B.P., Calluna heath and grassland appear to be well established in north Arran.The history of Sorbus spp. is examined in as much detail as the fossil evidence allows. By around 6500 B.P., Sorbus aucuparia L. is present in the area, and by around 5400 B.P., evidence for non-aucuparia Sorbus species is present. This evidence may represent the former presence of 5. rupicola (Syme) Hedl. and/or one or both of the two endemic species S. arranensis Hedl. and 5. pseudofennica E. F. Warb.

Vegetational history and land use: a radiocarbon‐dated pollen diagram from Machrie Moor, Arran, Scotland

“…The date from Machrie Moor is markedly younger at 8665+ 155 B.P. This date is confirmed by one from Loch a'Mhuillin in the north of the island (Boyd & Dickson, 1987). It seems likely that the migration of Corylus to Arran was delayed by the deep water trough surrounding the island and it has been suggested that it owed its eventual arrival more to the activities of human populations than to natural dispersal (Robinson, 1981;Boyd & Dickson, 1986).…”

“…Prior to this work the only other published pollen analysis from the island was from the forecourt of a neolithic chambered cairn at Monamore, Lamlash (Durno, in MacKie, 1964) although there were diagrams from nearby Kintyre (Nichols, 1967) and Bute (Marshall, Scott & Whittington, 1976). An account of the pollen analysis of lake deposits from a Loch a'Mhuillin, a site near Lochranza in the north of Arran has recently been published (Boyd & Dickson, 1987).…”

The vegetational history of Glen Diomhan, North Arran, site of endemic whitebeams, Sorbus arranensis Hedl. and S. pseudofennica E.F. Warb.

“…Nevertheless, it is unfortunate that we do not know when the endemics first appeared in Glen Diomhan or whether they were ever rnore widespread in the area. Their appearance at Loch a'Mhuilinn is tentatively correlated with an opening up of the surrounding woodland (Boyd & Dickson, 1987a). Around Glen Catacol, however, it appears that the vegetation has been open throughout the Flandrian at least in the upper parts of the glen.…”

“…The estimation of the time scale is based upon correlations with other pollen diagrams, in particular those from Loch a'Mhuilinn (Boyd & Dickson, 1987a) and Machrie Moor (Robinson & Dickson, 1988). The sequence may have begun at or just before 8000 years BP.…”

“…The results presented here are part of a wider study of the local and regional vegetational history. Pollen analysis was also undertaken on sediments from a small loch to the northeast of Glen Diomhan, Loch a'Mhuillin (Boyd & Dickson, 1987a, Boyd et al, 1988, and on basin mire deposits from Machrie Moor, a low-lying area near the west coast in the southern half of the island (Robinson, 1981;Robinson & Dickson, 1988). A major aim of the work was to provide guidance for management of the nature reserve in Glen Diomhan.…”