EPILITHIC MACROLICHEN VEGETATION OF THE ARGENTINE ISLANDS, ANTARCTIC PENINSULA

Classification of 162 sample plots of lichen vegetation from the Argen tine Islands region, Antarctica, yielded two main groups, the Usnea co mplex and the Mastodia-Rinodina complex, comprising four and six subor dinate communities, respectively. Communities of the Usnea complex typ ically occur in inland sites with steep slopes, characterized by low c hloride, ammonia and phosphate concentrations. Communities of the Mast odia-Rinodina complex occur close to the shore and in areas occupied b y birds, where concentrations of chloride, ammonia and phosphate were relatively high. Within each vegetation complex species composition is related to factors indicating nutrient status (chloride and ammonia c oncentration, distance from the sea), as well as to variables indicati ng different microclimatic conditions (elevation, aspect, exposure, mo isture, and gradient). In canonical correspondence analyses of the dat a a large part of species variation could not be explained by the envi ronmental variables studied (elevation, gradient, slope aspect, distan ce from the sea, direction of the sea, presence of guano, exposure, mo isture, chloride, ammonia, phosphate and nitrate concentrations). It i s suggested that temporal variability in mineral concentrations and th e lack of information on differences in length of the growing season a t the sample sites are, to a large extent, responsible for this.