SUMMARY Palacoecoiocical investigations of two lake sediment sequences are used to reconstruct the vegetation history of the Western Isles. Pollen records begin in the late glacial and show a clear progression From herb‐rich grassland with abundant Salix, Rumex and Poly‐podium to widespread Empetrum nigrum heath. Woodland developed widely in the early Holocene, and regional vegetation patterns emerged. Western Lewis supported extensive areas of birch woodland with Corylus avellana, Salix, Populus and Sorbus aucuparia. Open birch‐hazel woodland dominated other lowland regions. Regional variation was accentuated when woodland underwent a sudden decline in western Lewis at about 7900 BP. Trees were replaced by blanket peat and woodland failed to recover on a regional scale after the decline‐ Woodland continued to diversify in central and eastern regions and, by 6000 BP, Quercus, Ulmus, Pinus sylvestris, Alnus glutinosa and Fraxinus excelsior had become established. Open mixed woodland persisted until the second major decline began between 5200 and 4000 UP. Woodland contracted gradually as blanket peat expanded. The Western Isles were predominantly treeless at 2500 BP. Blanket peat started to form in localized areas on the Western Isles between 9000 and 8000 BP; two main expansion phases are associated with periods of woodland decline. Sublossil wood or macrofossils are reported from a total of 40 sites. Radiocarbon ages are presented for 13 samples of these.

A Holocene record of pollen, charcoal, magnetic susceptibility and sediment chemistry from South Uist, Western Isles, IS described and discussed. The vegetation of eastern South Uist included areas of woodland over as much as half of the available landscape during the early postglacial. This woodland was dominated by Betula and Corylus, but Quercus, Ulmus, Alnus glutinosa and Fraxinus excelsior were also present. The status of Pinus sylvestris IS uncertain. Quercus, Ulmus and A. glutinosa are now extinct as native trees in the Western Isles. During the later half of the Holocene (from about 4000 BP), woodland declined, possibly as a result of the use of hill land as grazing. Blanket peat vegetation, which had begun to spread from about 5500 HP, became the dominant feature of the landscape as the woodland areas decreased. The physical and chemical data from Loch Lang sediments suggest that little erosion of soils took place until about 550 years ago, when there vvas a marked increase, possibly attributable to increasing grazing pressure. Key words; Holocene, vegetation history, radiocarbon dating, sediment chemistry. Western Isles. INTRODUCTION°^ bedrock geology, and the treeless aspect of the Western Isles relative to the mainland at the same he Western Isles of Scotland, lying on the latitude has been explained by their greater degree of northwestern fringe of Europe and exposed to a wet exposure to wind. This introduces a strong east-west ana windy oceanic climate, are today virtually gradient to syntheses of Scottish vegetation (e.g. treeless. Their landscape is, for the most part, during the historical period [McVean & Ratcliffe, aominated by blanket peat up to several metres 1962] or at 5000 BP [Bennett, 1989], Is this view of t ick. The islands extend nearly 190 km from north the Western Isles supported by palaeoecological to south, from the latitude of Fort William to that of data? In the only modern works on the Holocene ape Wrath. Perhaps because they form a discrete vegetation history of the Western Isles, Birks & geographical unit, there has been a tendency to treat Madsen (1979) suggested that at least western Lewis e islands as uniform in vegetational terms, had been mostly treeless throughout the Holocene. a though the same latitudinal extent on the west Bohncke (1988) argued that the Callanish area, also cottish mainland coast covers a range of vegetation in western Lewis, supported local Betula woodland ypes from oak-dominated woodlands, through pine that was severely affected by anthropogenic burning, and birch to generally unforested areas of the Wilkins (1984) has drawn attention to the abundant northwest mainland. The vegetational richness and macrofossil remains of trees, including at least one variety of Skye, entirely within the latitudinal range species now extinct as a native tree in the Western o the Western Isles, are well-documented (e.g. Isles {Pinus sylvestris), within the blanket peat of irks, 1973). At least in part, there may be a Lewis and Harris. The palaeoecological and hisve...

Modern pollen rain in three unforested regions in the northwest of the British Isles is investigated using surface sediments from 64 small lakes (mean size 1.5 ha). Pollen assemblages from Shetland and the Western Isles accurately reflect the predominance of blanket peat vegetation on the islands and combined frequencies for the three main taxa, Calluna vulgaris, Gramineae and Cyperaceae, exceed 65% at all sites. The proportion of tree and shrub pollen is small (7-24%). Variation in pollen representation is much greater in surface samples from Donegal, Ireland; tree and shrub pollen frequencies range from 12-52% and have a mean of 30.1%. Concentrations and accumulation rates indicate that the pollen production capacity of blanket peat vegetation is comparatively high and is within the range for boreal woodland. Pollen assemblages from remote Scottish islands are not overwhelmed by long-distance inputs; a mean of 11.3% on Shetland and 13.8% on the Western Isles is thought to have originated from off-island sources. Small lakes in a treeless landscape record regional pollen signals and recruit a large proportion of pollen from outside the immediate catchment areas.

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