Home – Home – Jornals – Flora and Vegetation of Asian Russia 2024 number 3

As climate aridity increases, the bioclimatic districts of Tyva form the following series: semihumid district - semiarid district of “rain shadow” - semiarid district - arid district. In this series the upper boundary of the steppe belt varies from 900 to 2300 m above sea level. The purpose of this work is to identify and analyze the patterns of steppe distribution in different bioclimatic districts of Tyva. 800 steppe geo-referenced geobotanical releves have been used. These releves have been attached to 15 associations of floristic classification; units of phytocenotic classification of different ranks have been assigned to them. Releves of one steppe association from one bioclimatic district have been brought together in one group, 22 steppe groups have been deliniated. In the mountains, mosaic of plant communities is determined by humidity and heat supply. The humidity values have been calculated according to the scale of humidity optima; as a criterion of heat supply, the values of height above sea level have been used. In the coordinate system “humidity - height above sea level”, schemes of ordination of 22 steppe groups have been made; differences in their humidity and height above sea level have been statistically verified. Meadow steppe, tussock steppes, bunch-grass steppes with Carex pediformis , bunch-grass steppes and desert steppes with Nanophyton grubovii are found to form a series of humidity decrease, the difference of neighboring steppe types is statistically significant. Widespread in Tyva mountains stony habitats in the semihumid district are covered with background steppes. In semiarid districts, the rocky slopes of steppe belt become the neighboring belt steppe “outposts”; in forest-steppe belt, the rocky slopes wear specific petrophytic bunch-grass steppes. In the arid bioclimatic district, stony habitats retain background steppes. In terms of humidity, the petrophytic bunch-grass steppes and bunch-grass steppes with Carex pediformis have no significant differences. For each bioclimatic district an ordination scheme and a description of steppe vegetation have been compiled. In semihumid and arid districts, 4 steppe associations have been noted in each of them, and 8 steppe associations have been recorded in each semiarid district. The spectra of steppe communities in each bioclimatic district are unique. The steppe vegetation of arid district is the most original (similarity coefficients are 0-0.08), and steppe spectra of semiarid districts are similar (similarity coefficient is 0.64). The geographical distribution of the steppe associations has been modeled using MaxEnt. In the resulting models, the AUC values for training and test samples are 0.96-0.99. The potential area unites the territory where the probability of community finding exceeds 0.5. It has been revealed that the areas of steppe communities in Tyva outline а mosaic of mountain basins and surrounding mountain ranges. The areas of meadow and tussock steppes delineate the boundaries of forest-steppe landscapes, bunch-grass steppe area limits the steppe belt, and desert steppes with Nanophyton grubovii or Stipa glareosa indicates desert-steppe landscapes. Potential area of steppe habitats was found to hold a quarter of Tyva territory. The largest part belongs to bunch-grass steppes with Carex pediformis (31 %), the smallest one - to desert steppes (3 %).