Differentiation of forest vegetation across bioclimatic sector border (western part of the West Sayan Ridge)

A detailed description of the forests of the northern and southern macroslopes of western part of the West Sayan Ridge has been performed and differences in their forest vegetation have been analyzed. Along the West Sayan Ridge watershed, the important botanical and geographical boundary of the Altai-Sayan Mountains occurs. Its northern macroslope belongs to the humid bioclimatic sector; bioclimatic conditions throughout the southern macroslope vary in its different parts: the central and eastern parts are resided in the semihumid sector, while the western one is settled in the «rain shadow», where vegetation is similar to the semiarid sector one. The West Sayan background vegetation type is forest. The work is based on 120 complete geobotanical relevés made by the authors in 2019 using standard methods on test plots of 20 × 20 m. These plots had been uniformly distributed on a 300-kilometer transect crossing the northern and southern macroslopes of West Sayan’s western part. After all, 9 basic units of forest communities have been revealed, 6 of them are found to be altitudinal zone forests. These plant community positions in ecological-phytocenotic and floristic classification hierarchy have been ascertained. The altitudinal allocation and areas of altitudinal zone forests have been characterized and analyzed; the scheme of altitudinal zonation has been specified; the pictures in the text illustrate those results. In West Sayan’s western part, the northern and southern macroslopes are shown to have different altitudinal zone boundary marks and a different set of forest communities: six types of forests follow each other from north to south throughout 300 km. The significant hierarchical level of syntaxonomic differences of altitudinal zone forests on northern and southern macroslopes supports the presence of a bioclimatic barrier. In ecological-phytocenotic classification hierarchy these differences are reflected by the rank of classes of formations (deciduous, dark coniferous, and light coniferous forests substitute each other); in floristic classification hierarchy – the rank of classes (the forests of Brachypodio–Betuletea, Asaro–Abitetea, Vaccinio–Piceetea, and Rhytidio–Laricetea substitute each other from north to south).