Middle oroarctic vegetation in Finland and middle-northern arctic vegetation on Svalbard

Risto Virtanen and Seppo Eurola. 1 997. Middle oroarctic vegetation in Finland and middle-northern arctic veg­ etation on Svalbard Acta Phytogeogr. Suec. 82, Uppsala, 60 pp. ISBN 9 1 -72 1 0-082-6. (9 1 -72 1 0-482-5 . ) Plant communities of the middle oroarctic zone of northwestern Fennoscandia and middle-northern arctic areas of Svalbard were studied to describe the community types and their ecological relationships. The analyses were based on data sets collected both from subcontinental mountains of Finnish Lapland and from a geographically broad area of Spitsbergen, the main island of Svalbard. Plant communities were classified by a divisive clus­ tering method (TWINSPAN) and the ecological relationships of the community clusters were examined by detrended corre­ spondence analysis (DCA) . For northern Fennoscandia, edaphical ly differentiated series of community types from wind­ exposed ridges to depression sites with snowbed vegetation were described. On siliceous substrates, the types in the series con­ formed to those described earlier. On calcareous soi l , the Dryas octopetala-Carex rupestris type occupied exposed ridges, the Cassiope tetragona-Dryas octopetala type sites with moderate snow cover, and the Salix polaris-Silene acaulis type moderate snowbed sites, while late snowbed sites harboured communities of the Saxifraga oppositifolia-Ranunculus sulphureus type. For Spitsbergen, the following three regionally distinguished series were described: ( 1 ) In the inner fjord region, wind-swept ridges were character­ ized by the Saxifraga oppositifolia-Hypnum revolutum com­ munity. This community shows a gradual transition to com­ munities rich in Dryas octopetala and mosses on sheltered slopes. (2) At the southwestern-western coastal region, ridges were occupied by communities characterized by Racomitrium lanuginosum. These graded to moss and lichen-rich heaths, while depression sites harboured snow bed communities domi­ nated by Sanionia. (3) In the Dryas region, ridge heaths approached the vegetation of polar deserts. The sheltered sites were characterized by moss tundra communities and Sanionia snowbeds. On the mountains of northern Fennoscandia, the plant com­ munities seemed to be clearly differentiated in relation to the bedrock. On Spitsbergen, some edaphic differentiations exist among plant communities, but some of the differences obviously reflected climatic differences among the areas studied. It was shown that the sheltered slopes and snowbed sites of Spitsbergen harbour copious moss vegetation dominated by robust (mainly pleurocarpic) mosses, whereas the corresponding habitats in northern Fennoscandia seem to consist of small bryophytes growing together with prostrate vascular plants and lichens. One reason for this may be the absence of herbivores (Norway lemming or brown lemming) feeding on mosses on Spitsbergen. Nomenclature: Vascular plants (Lid & Lid 1 994), bryophytes (Soderstrom et al. 1 992) and lichens (Santesson 1 993 ; Andreev et al. 1 996). Risto Virtanen and Seppo Eurola, Department of Biology, Uni­ versity of Oulu, P 0. Box 333, F/N-90571 Oulu, Finland. Acta Phytogeogr. Suec. 82