TOPOGRAPHIC AND ALTITUDINAL PATTERNS IN PLANT-COMMUNITIES ON EUROPEANARCTIC ISLANDS

Vegetation on Bear Island, Jan Mayen and Spitsbergen was investigated along altitudinal and topographic gradients in order to describe the m ain patterns in plant community distributions and compare them with th ose on the mainland. In a numerical classification the communities wer e distinctly differentiated; however, physiognomically similar Racomit rium and Sanionia communities dominated in most habitats on Bear Islan d and Jan Mayen. On Spitsbergen, moss-dominated communities prevailed in depression sites. High-altitude sites were occupied either by moss- dominated communities or by variable assemblages of fragmented moss co ver and scattered vascular plants. Dwarf shrub and grass heaths that w ere common on the mainland did not occur on grazer-free Bear Island an d Jan Mayen, and were confined to the lowest altitudes on Spitsbergen. The lack of grazers on Bear Island and Jan Mayen accounts in part for the differences in vegetation between the mainland and the islands.