The stages of vegetation development close to two glacier fronts on two of the South Shetland Islands (Livingston and Robert) within the Maritime Antarctic were studied with special reference to saxicolous lichens. A lichenometric study of the crustose lichen Caloplaca sublobulata was carried out at both sites. On the moraine of Livingston Island, rock size played an important role in lichen development, explaining most of the differences observed in the diameter of C. sublobulata, the number of species, and the percentage of cover among the rocks studied. On Robert Island, the distance from the glacier front was associated with the lichen cover of the rocks but not with diameter of C. sublobulata This homogeneous distribution of C. sublobulata thallus size on the Robert Island study area points to a simultaneous recolonization of the whole zone by this lichen. The lichen development in the area studied on Robert Island seems to have been drastically affected by fluctuations in the persistence of snow cover following glacier front retreat. Tentative associations between ice retreat and colonization, on the o e hand, and changes in snow cover duration and the dynamic processes of extinction and recolonization, on the other, are suggested from comparison of the two zones.

This paper describes two versions of a new method for detecting and examining spatial pattern in communities of crustose saxicolous lichens. One version is based only on the shapes of the lichen thalli and the second on the identity of their species. These methods are useful for examining the spatial structure of a lichen community for the presence of anisotropy, the phenomenon of having different scales of pattern in different directions. If present, the nature of the anisotropy has implications for our understanding of the processes that give rise to spatial pattern. Preliminary results from communities in the Canadian Rockies suggest that while individual species show some evidence of anisotropy, when all species are considered together, or when only the shapes of the thalli and their boundaries are considered, anisotropy is reduced or absent.

Lichens dominate the terrestrial vegetation of the ice-free regions of continental Antarctica. Vegetation patterns were studied in the Windmill Islands Oasis, Wilkes Land, continental Antarctica, in relation to edaphic features to elucidate the factors that govern lichen distribution and abundance. Vegetation was studied on a low rounded knoll on Clark Peninsula some 3 km North East of the present Casey station. Substratum nutrient levels vary considerably across the knoll due to the presence of an abandoned penguin rookery on the crest and the uneven topography provides both sheltered and exposed sites. Along a 130 m-long transect crossing the knoll from South to North, a total of 25 species of lichen and one moss were identified, the vegetation being dominated by Umbilicaria decussata, Pseudephebe minuscula, Usnea sphacelata and U. antarctica. TWINSPAN analysis of species distributions identified six sociations, the distribution of which were related to substratum structure and chemistry. Several species were restricted to nutrient-rich zones while late-lying snow restricted all species to varying degrees.

Five populations of the circumpolar Arctic-alpine lichen species Cetraria nivalis were sampled along a latitudinal gradient from the temperate to the Arctic climatic zone. The populations were compared with respect to their CO2 exchange, water relations and morphology/anatomy. Provenances from places along this latitudinal gradient were transplanted in 1983/84 to a site near the Scientific Research Station in Abisko, to see whether they are identical with plastic acclimation ability or whether they represent different ecotypes. The five populations represent two major geographical groups, a ‘southern’ and a ‘northern’ one, with respect to some morphological and anatomical features, chlorophyll content and water relations. The transplanted C. nivalis provenances showed a tendency towards increasing net photosynthetic rates with origin in the higher latitudes. The CO2 exchange response of the native populations was the reverse of this tendency although CO2 exchange was in general flexible. It is concluded that the investigated C. nivalis populations were different ecotypes because of genetic differences and a distinct seasonal plasticity. The ecotypes are interpreted as a result of isolation in different refugia during the Pleistocene.

Primary production in lichens, as in all plants, is the result of gains and losses. Losses of carbon may be high under extreme environmental conditions. In the harsh climate of polar regions lichens use much carbon for maintenance and in their stress response. Thallus biomass is preserved through periods of darkness, extremely low temperatures and snow cover. On the other hand, lichens are photosynthetically active at temperatures below 0°C. They can make use of melted water from snow and ice and take up water vapour from snow. Physiological adaptations and environmental conditions under which growth is possible are discussed in terms of our recent results. A concept model describes the main parameters that influence carbon acquisition, growth and water relations of lichens in polar regions.