PRIMARY SUCCESSION OF PLANT ASSEMBLAGES ON A GLACIER FORELAND - BODALSBREEN, SOUTHERN NORWAY

Primary successions on glacier forelands have been widely described as changes of plant assemblages, although many studies show that the ass emblages may be more apparent than real. Some doubt has also been cast on the occurrence of successional convergence on deglaciated terrain. Vegetation data from five dated terminal moraines in southern Norway, created between 1750 and 1930, were classified by TWINSPAN. The disti nctness of the TWINSPAN groups and their relation to the spatial and t emporal gradients were analysed by Canonical Correspondence Analysis. The successional sequence can be described as a physiognomic developme nt; from cryptogam-mats, to a heath-phase, which may then be over-grow n by Betula shrubs that develop into a sub-alpine Betula pubescens for est. Most species (79%) in the Racomitrium canescens and Stereocaulon assemblage on the youngest moraine are also found in the Betula pubesc ens forest on the oldest moraine. However, the establishment of some s pecies seems to be facilitated by other species. The floristic differe nce between the TWINSPAN groups decreases with time suggesting that su ccessional convergence has occurred. The spatial micro-variation is re duced once a closed canopy of Betula is established on the oldest mora ine, but there are clear variations related to moraine positions on th e other moraines.