Late Quaternary vegetation history of the Western Isles of Scotland.

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.