Zonation in the plant cover on the Wrangel Island: syntaxonomical approach
Authors: Kholod S. S. 
Published: February 2020

Hierarchical subdivision of the Wrangel Island was realized using syntaxonomic method. Following criteria were used: syntaxonomic spectrum and percentage share of syntaxa on zonal and intrazonal sites, the status of syntaxa in the system of altitudinal belts, the indexes of zonation and intrazonation, the index of dissimilarity between syntaxa (І-diversity) and mean number of species per relevй. The system of zonocontinuums and the criterion of typomorphic groups were applied to represent the character of syntaxa distribution. Furthermore, the indexes of “species-area relationships”, zonal-geographical groups of species, cover of the different groups of species and its variation, horizontal structure of communities and above ground phytomass were reviewed. All numerical characteristics allowed to make a differentiation of the island vegetation between 4 variants. Among these 2 ones are southern and nothern variants of arctic tundra subzones, 1 — is northern variant of typical tundra subzone and 1 — is southern (coastal) variant of polar deserts. The last are delimited fr om other zonal categories in highest rank —as geobotanical zone. They are characterized by minimum number of syntaxa in zonal sites (4) and in flood-plains (2), absence of any syntaxa at the slopes of southern exposure. All other indexes of diversity are of a least value: dissimilarity between syntaxa (43.7), and average number of species in relevй (5.9). Differentiate syntaxa for all sites (except plakkat) and typomorphic groups are absent. It is a least value of і-diversity: the parameter b1 in regression equation is1.17. Moreover, the cover of vascular plants decreases to 10–20 %, but cover of lichens increases to 30 %. The cover of bryophytes and all vegetation are characterized by essential changes of variation coefficient (0.6–0.7 and 0.4–0.5 respectively), above ground phytomass of vascular plants is decreases to 49.9 g/m2. The part of arctic zonal-geographical groups is increases greatly to 61.4 %, but total part of hypoarctic and boreal is decreases to 3.8 %. Sporadic-spotted type of horizontal structure is exclusively peculiar to this zone. Northern variant of typical tundra is characterized by a relatively large number of syntaxa at slopes of southern exposure (19) and high value of index of abruptness (0.56). Number of syntaxa with diagnostic meaning of altitudinal changes is greater — 13. The index of І-diversity by means average number of species in relevй is 9.5 and by means dissimilarity between syntaxa is 55.1 %. High diversity of syntaxa (9) differentiating at slopes of southern exposure is inherent to this zonal variant. Besides, large role of hypoarctic species (10.8 %), irregular-mosaic type of horizontal structure and relatively large overground phytomass of vascular plants (89.9 g/m2) are characterized for this zonal category. Here it is the highest value of і-diversity (b1 = 3.07). Southern and northern variants of arctic tundra are characterized by parameters distinguished from the plant cover of polar deserts zone and typical tundra subzone. These parameters are: number of syntaxa at slopes of southern exposure (11 and 8), their index of abruptness (0.36 and 0.29), number of syntaxa with diagnostic meaning of altitudinal changes (8 and 5), indexes of І-diversity (60.0 and 58.5 — dissimilarity between syntaxa, 7.9 and 8.2 — average number of species in relevй). Moreover, similar values of і-diversity (b1 = 2.30 and 2.50), zonal-geographical spectrum (wh ere total part of hypoarctic and boreal groups is smaller essentially then in typical tundra, but part of arctic group is equal to one of polar deserts) and above ground phytomass of vascular plants (83.5 g/m2and 80.1 g/m2) are peculiar to these two variants. Several vegetation indexes contribute to reveal southern and northern zonal variants. The last region is referred to the High Arctic. Also diagnostic amount of syntaxa and analytical characteristics for zonal categories of definite rank were determined. Typical syntaxa have a special significance for zonal categories of higher rank (tundra zone as whole and the subzone of arctic tundra).