Phytogeographical specificity of bogs of the northwestern Karelian Isthmus (Leningrad Region)

The vegetation of the bogs of the northwestern part of the Karelian Isthmus is characterized. Main attention is paid to oligotrophic, ridge-hollow massifs which are reference for the southern half of the taiga zone, and have reached the ridge-pool stage of development. It was found that the bog vegetation of this part of the Karelian Isthmus differs from that of the rest of the Leningrad Region, having features that bring it closer to the vegetation of the bogs of the Baltic Sea coast. Trichophorum cespitosum occurs constantly, in places abundantly, on the ridge-pool sites of these bogs. Chamaedaphne calyculata is missing. In the herb-dwarf-shrub layer of the ridges, Calluna vulgaris holds undivided dominance, while Rhynchospora alba dominates in the hollows. In the moss layer, Sphagnum cuspidatum dominates in most hollows, S. tenellum in some massifs, and S. rubellum is often found and sometimes dominates on ridges. In the bogs of this part of the Isthmus, both Sphagnum divinum and S. medium grow, their ratio in terms of occupied area and frequency of occurrence varies in both different and sometimes neighboring massifs, and a trend to a gradual decrease of the share of Sphagnum medium along the west–east gradient is observed. Also, they ocupy different habitats. There are few lichens on the ridges, and they do not play any phytocenotic role in the studied bogs. The bogs of the studied area differ sharply in vegetation from the bogs of the South Karelian and East Baltic mire provinces, having many similarities with the bogs of the Baltic Coastal province.