The vegetation of frozen peat palsa of mire complexes in the north of Western Siberia and Taimyr peninsula

Abstract

The vegetation of frozen peat mounds and polygons of palsa bogs as well as tundra-mire complexes, according to the Braun-Blanquet classification, is assigned to Oxycocco-Sphagnetea class Br.-Bl. et Tx. ex Westhoff et al. 1946 (Koroleva, 2006; Lavrinenko and Lavrinenko, 2015; Telyatnikov et al., 2021; Jiroušek et al., 2021) and considered within two alliances – Oxycocco microcarpi–Empetrion hermaphroditi Nordhagen ex Du Rietz 1954 and Rubo chamaemori–Dicranion elongati Lavrinenko et Lavrinenko 2015. However, the data on the phytocoenotic diversity of these mire types are very scarce. Our research was conducted between 2004 and 2019 in the northern part of the Khanty-Mansi and the southern part of the Yamal-Nenets Autonomous Areas of the Tyumen Region at 20 study sites (Fig. 1) located between 63° and 75° N in the northern taiga, forest tundra and southern tundra of West Siberia. Additionally, we used relevés obtained in 2021 at 3 study sites at the northern boundary of the larch woodland sub-zone and in the southern tundra of the Taimyr Peninsula in the middle reaches of the Dudypta River (70.5°–71.5°N and 90.5°–95.0°E). Seven associations, 9 subassociations and 9 variants (Tables 1–6) have been identified in the class Oxycocco-Sphagnetea on the base of 376 vegetation relevés of palsa bogs and tundra-mire complexes. Furthermore, 567 previously published relevés of ecologically similar syntaxa from the adjacent regions (Koroleva, 2006; Lavrinenko and Lavrinenko, 2015; Telyatnikov et al., 2021; Lavrinenko et al, 2022) were used for statistical processing and comparative analysis. A comparison of all identified and previously described syntaxa in similar habitats of the Russian Subarctic were made (Table 7). Statistical processing and t-SNE ordination (t-distributed stochastic neighbor embedding method) (van der Maaten, Hinton, 2008) of the entire data set was performed to confirm the classification results (Fig. 11). Cluster analysis (Fig. 12) showed a significant difference between the 4 groups of syntaxa at a high hierarchical level. Two clusters, I and IV (Fig. 12) are assigned to the earlier described alliances Rubo chamaemori–Dicranion elongati and Oxycocco microcarpi–Empetrion hermaphroditi. The alliance Rubo chamaemori–Dicranion elongati comprises shrub-moss (Dicranum elongatum, Polytrichum strictum)-lichen communities on dry frozen peat mounds of oligotrophic palsa bogs and polygonal mires in the forest tundra and tundra zone of European Russia. It includes 4 associations (Fig. 11, 12) Tephroserido–Politrichetum stricti, Rubo chamaemori–Dicranetum elongati, Pleurozio schreberi–Caricetum globularis, Rubo chamaemori–Caricetum rariflorae, previously described on the east coast of the Kola Peninsula and in the East European tundra (Koroleva, 2006; Lavrinenko, Lavrinenko, 2015; Lavrinenko et al., 2022). The alliance Oxycocco–Empetrion hermaphroditi includes open and forested dwarf shrub-Sphagnum communities of relatively dry hummocks and ridges dominated by Sphagnum fuscum on ombrotrophic raised bogs in the boreal and forest-tundra zones of Eurasia. The alliance is represented by a single ass. Ledo palustris–Sphagnetum fusci occurred on frozen bogs in the north of Western Siberia. We consider this association in the narrow sense (sensu Du Rietz, 1921), including only non-forested dwarf shrub-Sphagnum (S. fuscum) communities of subarctic subcontinental regions of Europe and Western Siberia. Two new alliances, along with the previously described ones are proposed (Fig. 12, clusters II and III) – Rubo chamaemori–Cladonion stygiae all. nov.and Sphagnion lenenses all. nov. (Table 8). They combine dwarf shrub-lichen communities of palsa bogs of the northern forest taiga zone in Western Siberia and oligotrophic dwarf shrub-cotton grass-lichen-Sphagnum communities with S. lenense and S. balticum in raised bogs of Asian part of the Subarctic, respectively. The alliance Sphagnion lenenses is represented by the recently described ass. Ledo decumbentis–Eriophoretum vaginati (Lavrinenko et al., 2022). Based on additional data from the southern tundra zone of Western Siberia and the Taimyr Peninsula, two new subassociations are described within the association L. d.–E. v. sphagnetosum lenenses and cladonietosum amaurocraeae. The alliance Rubo chamaemori–Cladonion stygiae includes 3 associations, replacing each other from south to north: ass. Ledo palustris–Cladonietum stygiae ass. nov. with 2 subass. L. p.–C. s. typicum, and sphagnetosum fusci, differing by the ratio of mosses and lichens in the ground cover (northern taiga) → ass. Cladonio stygiae–Caricetum globularis with 2 subass. C. s.–E. v. typicum and salicetosum pulchrae (forest tundra) → ass. Sphagno lenenses–Cladonietum stygiae (southern tundra). We also assigned conventionally the Ledum palustre–Polytrichum communities (ass. Ledo palustris–Polytrichetum stricti) to the same alliance. They represent the long-term successional stage in the post-fire restoration of the dwarf shrub (Ledum palustre)-lichen vegetation of frozen peat palsas. Despite a relatively small number and wide ecological amplitude of the majority of dominant and constant species in raised bog communities of Oxycocco-Sphagnetea, the species constancy and abundance (phytocoenotic activity) in communities of various alliances differ clearly, which makes it possible to identify the differential species combinations (Table 8). Two alliances described here and previously known all. Rubo chamaemori–Dicranion elongati are assigned to the new order Rubo chamaemori–Cladonietalia arbusculae ord. nov. Differential species combination of the alliance Rubo chamaemori–Dicranion elongati (having a central position in the order), is common to all communities of the class Oxycocco-Sphagnetea in the Subarctic. These species are proposed as diagnostic species of the new order: Betula nana, Cladonia arbuscula, C. amaurocraea, C. rangiferina, C. stygia, Dicranum elongatum, Empetrum nigrum s. l., Flavocetraria cucullata, Polytrichum strictum, Rubus chamaemorus, Vaccinium vitis-idaea subsp. minus. The order Sphagnetalia medii Kästner et Flössner 1933 is represented in the north of Western Siberia by only one alliance — Oxycocco microcarpi–Empetrion hermaphroditi, common mainly in the boreal forest zone. The new structure of the class Oxycocco-Sphagnetea shows the major zonal and sectoral-geographical categories of mire vegetation in Northern Eurasia. The involvement of the entire volume of relevés data set and the expansion of the survey to the boreal zone and eastern regions of Russia will allow the hierarchical structure and differences of higher units in the class Oxycocco-Sphagnetea to be more clearly demonstrated.