Vegetation Pattern in a Moss: Lichen Heath Associated with Primary Topographic Features on Jan Mayen

Abstract

The distribution of cryptogams across a ridge-hollow system was assessed by estimating percentage cover along a transect of contiguous quadrats and correlated with exposure to the prevailing northerly wind, winter snow lie, aspect, and inclination. Stereocaulon species are the most tolerant of wind ex- posure, followed by Rhacomitrium lanuginosum. Rhacomitrium canescens and Cladonia mitis are both associated with late snow lie, the latter species being lim- ited to the most favorable habitats in respect to aspect and inclination. The vegetation of Jan Mayen Island (7100'N, 8030'W) has been described in out- line by Russell and Wellington (1940). The porous nature of the basaltic rocks, the thin and immature soils together with the rigors of the subarctic climate limit the development communities dominated by higher plants to small areas with a particularly favorable environment. The greater portion of the vegetation of the island consists of a moss mat dominated Rhacomitrium lanuginosum (Hedw.) Brid. and R. canescens (Hedw.) Brid. (Wilson, 1952), but little attention has been paid to the ecology of these communities. of a series of ridges with amplitudes of 1-6 feet (0.3-1.8 meters) and orientated in different parts of the lava field towards diverse points of the compass. These ridges are primary topographic features formed by surface cooling of the molten lava flows. The flows belong to the last major eruption cycle of the volcano Beerenberg, the Koksletta Formation (Fitch, 1964), and have been dated at 2,500-3,500 years old. The lava platform is open to the sea on the north, west, and south sides but sheltered immedi- ately to the east by fossil sea cliffs of the older Tromsoryggen Formation and to the