Vegetation of exposed calcareous ridges in central Spitsbergen, Svalbard, Norway
Nilsen, Lennart; Elvebakk, Arve
Vegetation of exposed calcareous ridges has been studied at Sassendalen, Central Svalbard, by 111 relevés, each 100 m 2 large. A classical detrended correspondence analysis (DCA) ordination technique was applied to the floristic data. Relevé scores along DCA axis one was subjected to an agglomerative clustering technique and four plant communities were distinguished. Results showed that three subtypes of a Potentilla pulchella community were basically very different from a Dryas octopetala-Cassiope tetragona community. The latter is a well-known and well-documented, widespread arctic-alpine ridge community, but was here confined to the lowermost part of the ridges. The Potentilla pulchella community has no affinity to alpine communities, although it has previously been interpreted as belonging to the alliance Arenarion norvegicae, described from Fennoscandian limestone screes. The community has several high arctic character and preferential species, such as Potentilla pulchella, Poa abbreviata, P. hartzii, Puccinellia angustata, Braya glabella ssp. purpurascens, and Poa arctica ssp. caespitosa. Its weakly convex landform and silt-dominated substrate is geomorphologically a non-littoral lowland habitat with very low vegetation cover (4 to 14 %). The three subtypes of Potentilla pulchella communities are distributed along a topographical gradient above the Dryas community, reflecting different degrees of exposure. In addition to desiccation and alkalinity, strong cryoturbation during early spring may also be a limiting factor, explaining the low vegetation cover as well as abrasion by wind-driven snow, silt and sand. There is apparently no satisfying subdivision of the community yet, and the whole complex needs to be compared with what has been indicated as 'high arctic steppe' vegetation in the most continental parts of Svalbard.