The diversity and ecological-phytocoenotic characteristics of the birch krummholz (Betula tortuosa Ledeb.) in Altai-Sayan mountain region

The birch krummholz with Betula tortuosa Ledeb dominance occur in the most humid regions of Kuznetsky Alatau, Altai and Eastern Sayan within the Altai-Sayan mountain system (Zolotovskiy, 1938; Kuminova, 1960; Malyshev, 1965; Maskaev, 1976; Sedelnikov, 1979, 1988; Zibzeev, 2006). Mean annual precipitation in the Kuznetsky Alatau is 2000 mm (up to 3000 mm in some years). In the Tigirekskiy ridge study area the precipitation is 1500 mm. The deep snow (up to 1.5 m) protects grounds fr om freezing. The birch krummholz occupy the large areas on the variously exposed slopes at 950–1200 m in the Kuznetsky Alatau and at 1250–1350 m in Altai. These communities, known only in three places of the Altai-Sayan mountain system and listed in the ”Green Book of Siberia“ (1996), occur in the lower and middle parts of the subalpine belt on permanently moist slopes. According to the Braun-Blanquet approach the birch krummholz of the studied area are represented by three associations, two subassociations and one variant (ass. Cirsio heterophylli–Stemmacanthetum carthamoidis Zitluchina ex Ermakov et al. 2000, subass. C. h.–S. c. betuletosum tortuosae nov. hoc loco, ass. Doronico altaicae–Betuletum tortuosae nov. hoc loco, ass. Abieteto sibiricae–Athyrietum distentifoliae Ermakov et al. 2000, subass. A. s.–A. d. sorbetosum sibiricae Ermakov et al. 2000, var. Betula tortuosa). The birch krummholz of the Tigirekskiy ridge are referred to ass. Violo disjunctae–Betuletum tortuosae nov. hoc loco, and three subassociations (V. d.–b. t. typicum nov. hoc loco, V. d.–b. t. saussureetosum frolowii nov. hoc loco, V. d.–b. t. dracocephaletosum grandiflori nov. hoc loco.). All syntaxa are included into Mulgedio-Aconitetea Hadac et Klika in Klika et Hadac 1944 class, Trollio–Crepidetalia sibiricae Guinochet ex Chytry et al. 1993 order, Aconito pascoi–Geranion albiflori Zhitlukhina et Onishchenko ex Ermakov et al. 2000 alliance. The geographical isolation of birch krummholz affects their species composition and coenoflora structure. There are 99 species in the coenoflora of the Kuznetsky Alatau birch krummholz and 108 species in the Tigirekskiy ridge. The latter coenoflora contains specific species that can be divided into two groups. The first group includes the endemics of the Altai as well as Altai-Sayan mountain system as a whole(Hedysarum theinum, Hieracium korshinskyi, Ptarmica ledebourii, Sanguisorba alpina, Viola disjuncta, ­Phleum alpinum, Phlomoides alpina, Dracocephalum grandiflorum). The second group is represented by forest and forest-meadow species absent in the birch krummholz of the Kuznetsky Alatau (Carex pediformis, Cruciata krylovii, Galium boreale, Geum rivale, Iris ruthenica, Melica nutans, Pyrola minor). The studied communities have exact ecological and topological localizations. In the Kuznetsky Alatau the tall-forb birch krummholz of C. h.–S. c. betuletosum tortuosae are mostly common at high leveled parts of the slopes (3–5°) wh ere they alternate with subalpine meadows. The birch krummholz of ass. Doronico altaicae–Betuletum tortuosae occupy moist, usually cold, habitats. In these communities with the remarkably reduced coenotic role of tall-forbs the herb layer is mainly formed by subalpine and alpine meadow species. The communities of ass. Violo disjunctae–Betuletum tortuosae with three subassociations occur in wet conditions on leveled terraces, as well as on relatively flat slopes (0–2°) close to the tree line. A specific feature of the Tigirekskiy ridge birch krummholz coenoflora is a large number of forest species.