Studies in the Post-Glacial History of British Vegetation: XII. Hockham Mere, Norfolk

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Abstract
Hockham Mere is the site of a lake situated near to Thetford just within the n.-e. margin of the East Anglian"Breck-land" , and drained in post-Tudor times. Stratigraphic examination has disclosed deep deposits of organic lake muds (nekron muds), and pollen analysis of these indicates the nature of vegetational changes of the region from the late-Glacial until historic time. Tree birches were present in late-Glacial time along with Betula nana and hybrids; a high non-tree/tree pollen ratio, high mineral content of the lake muds, and the presence of species or genera characteristic of open habitats, all point to the presence of some bare ground and incomplete forest cover. The pollen spectrum has a typical late-Glacial assemblage of types, and it is possible to recognise pollen-zones 11 and 111, which correspond to the Allerod climatic oscillation. In the late-Boreal period the lake dried up considerably: its boundary at this time has been established. Very late in its history it became overgrown by sedge-fen, and in its western portions developed an oligotrophic vegetation. In Boreal and early-Atlantic layers abundant finds have been recorded of the fruits of Naias marina : N. flexilis was found in zone VII or VIE. Numerous other records, chiefly of fruits and seeds of aquatic plants, are reported. After a period of dense forest growth through Boreal and early-Atlantic time, some clearance is recorded by the sharp rise in several categories of non-tree pollen, and this is attributed to clearance by Neolithic man. The disforestation was accentuated at a later time which cannot be certainly identified. These effects appear to demonstrate the anthropogenic and prehistoric origin of the great Breckland heaths.

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