DEVENSIAN LATE‐GLACIAL AND FLANDRIAN VEGETATIONAL HISTORY AT HOCKHAM MERE, NORFOLK, ENGLAND: I. POLLEN PERCENTAGES AND CONCENTRATIONS

The sediment and pollen stratigraphy of a radiocarbon‐dated sequence from a lake on the eastern margin of Breckland is described. The record extends from 12620 to 1620 B.P. From 12620 to 9560 B.P. the vegetation was an open Betula woodland. Movement of sand by wind was one factor keeping the vegetation open. Between 9560 and 9255 B.P. a denser Betula woodland developed, to be replaced by a closed woodland dominated by Corylus avellana, with Pinus sylvestris, Ulmus and Quercus. During this period, Quercus gradually replaced P. sylvestris on the local sandy soils. Corylus avellana remained the woodland dominant until about 7140 B.P., when it was replaced by Tilia cordata. Alnus glutinosa expanded in response to raised water levels at about 6800 B.P., Fraxinus excelsior became an important component of the local woods, also replacing C. avellana. The elm decline occurred in two phases, at 6000 and 4500 B.P. Substantial forest clearance did not begin until about 2500 B.P. The spread of heath vegetation on the Breckland began at about 2250 B.P.