PALEOBOTANICAL ANALYSES OF ERIOPHORUM AND MOLINIA TUSSOCKS AS A MEANS OF RECONSTRUCTING RECENT HISTORY OF DISTURBED MIRES IN THE HAUTE-ARDENNE, BELGIUM

Pollen analyses from tussocks of Molinia caerulea and Eriophorum vaginatum are compared with pollen and macrofossil analyses of peat cores collected in degraded Molinia fens and bogs from the Hautes-Fagnes plateau. The history and causes of the deterioration in plant cover are better traced by pollen records from tussocks than from cores because the upper peat layers are often compressed, burnt or decayed whereas tussocks build up rapidly. In the study area, Molinia fens and bogs are derived from Alnus or Betula woods which originated at about 7000 yr BP. From the Middle Ages, moderate burning, coppicing, grazing, mowing, heather cutting and Sphagnum scraping led to a dominance of Ericaceae on bogs and poor fens. At the beginning of the 20th century, abandonment of these traditional practices induced a massive but temporary flowering of Calluna which was then rapidly destroyed by the spread of tussock-forming Molinia after drainage and frequent burning. The base of the tussocks can be dated by using the pollen datum horizon reflecting the Picea plantations from the beginning of the 20th century. This guide mark allows calculation of the tussock accumulation rate which is estimated between 3 and 5 mm/yr.