Phytocoenotic assessment of ecotopes on avalanche tracks and debris flow deposits in the Aktru river upper reaches

In the Altai Mountains, according to forecasts, there will be an increase in avalanche and debris flow activity in the first quarter of the 21st century, which affects mountain ecosystems. The aim of the study was a phytocoenotic assessment of ecotopes on the avalanche tracks and debris flow deposits in the Aktru river upper reaches (the central Altai Mountains, 50°04'N, 87°45'E). We collected data in the lower slope of the valley (2150-2340 m a.s.l.) at the treeline. Geobotanical descriptions of vegetation are given according to AA Korchagin in 2015. The area of inventory plots under the forest canopy was 625 m² (25x25), and that of non-forest communities or forest fragments was 100-150 m². On the basis of geobotanical descriptions of communities, we determined humidity and trophicity of ecotopes according to ecological scales (Tsatsenkin IA et al., 1978). At the same time, the description status was calculated using the weighted average considering amplitudes of species tolerance. The mediated ordination of communities was carried out according to phytoindication statuses. A comparative analysis of the lists of vascular plant and moss species is presented according to ecological groups using the data of AV Kuminova with additions and groups of growth forms according to IG Serebryakov. The names of vascular plant species are mainly given according to "Identification book..", those of mosses are according to MS Ignatov and EA Ignatova (See Figure 1, Table). It was revealed that the total number of species, participation (number and/or cover) of the species of most ecological groups (xerophytes, xeromesophytes, mesophytes, hygromesophytes, psychrophytes and petrophytes) and the most representative species of growth forms (taproot, short- and long-rhizome perennial herbs) increased from the forest belt to the forest-tundra ecotone, whereas hygrophytes decreased (See Figure 1, Table). The trophicity, aeratibility, and coldness of the ecotopes increased, and humidification decreased. In the zone of avalanche accumulation, the absence of a tree layer and a well-developed shrub layer were indicators of frequent avalanches (more than once in 10 years). Here, the projective cover of the moss layer was lower and the role of psychrophytes and hygrophytes was higher in comparison with undisturbed communities (See Figure 1 B). In general, the parameters of ecotopes varied slightly. A relatively increased coldness and humidity and reduced trophicity of substrates were typical of birch (Betula fruticosa, B. rotundifolia) communities, and a lower humidity and increased trophicity of ecotopes were common for meadows. In the zone of debris flow accumulation, a 170-200-year-old tree stand had survived, the cover of herbaceous-dwarf shrub and mossy layers was lower, and the number of hygrophytes and psychrophytes, and short-rhizome herbs was higher, as compared with undisturbed communities. The ground cover composition was similar to that of the undisturbed forest 32 years after the debris flow event. The transit zone of the debris flow is, currently, a channel of temporary streamflow. A low similarity in species composition and cover and the highest number of hygrophytes, psychrophytes, petrophytes, and short-rhizome herbs were observed here, in comparison with all other communities (See Figure 1e, f, g). The vegetation parameters indicated colder poorly developed and periodically waterlogged ecotopes, in comparison with undisturbed communities. These ecotopes seem to be influenced by frequent external impacts at present: regular and short-term flows of melted spring and heavy rainfall water and mudflows or debris flows (once in 10 years) from the higher parts of the slope. A number of sites in terms of the degree of impact of geomorphological factors on vegetation and their ecotopes are as follows: undisturbed - debris flow (accumulation zone) - avalanche (accumulation zone) - debris flow (transit zone). The article contains 2 Figures, 1 Table and 34 References.

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