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Shrub expansion into arctic and alpine tundra is one of the prominent vegetation changes currently underway. We studied the expansion of shrub vegetation into high elevation tundra in the Kvarkush Range of the Northern Ural mountains, Russia. Age structure analysis of the dominant shrub Juniperus sibirica Burgsd. seems to support ongoing upslope advance of shrubs, a process particularly active in the second half of the 20th century. We found a close connection between the expansion of shrub vegetation and the general change in climatic conditions of the cold season (months with mean air temperature below 0°C from November to March). In general, the greatest influence on the distribution of J. sibirica is exerted by the climate conditions of the beginning (November–January) and the end (March) of the cold season. With increasing elevation, the correlation coefficients between the establishment of J. sibirica shrubs and the precipitation of the beginning of the cold season increased, and reached maximum values at the top elevation level of the study area. However, the upwards shift of J. sibirica into typical mountain tundra does not lead to changes in the ecological structure of vegetation at this stage, but simply a decrease in the area of mountain tundra. © 2020, Science Press, Institute of Mountain Hazards and Environment, CAS and Springer-Verlag GmbH Germany, part of Springer Nature.

In ХХ century shrub vegetation moves in high mountains. However we do not have any data about changes in species composition of vascular plants and lichens, and also in ground cover structure in case of Juniperus sibirica introduction. Vascular plants species composition of mountain tundra on Northern and Southern Ural is a great different in these regions. Species richness of vascular plants on Northern Ural is slightly less than on Southern Ural. We founded only 9 common species for both regions. Endemic plants species list includes 6 species, 2 of them are common for both regions. Species composition of lichens is significant similar. There are 20 common lichens species on Northern and Southern Ural. Species richness of macrolichens on Northern Ural is some bigger than on Southern Ural. We did not find any specific lichens. Introduction of J. sibirica and its different cover do not change species composition of vascular plants and lichens in mountain tundra communities. And also J. sibirica introduction do not lead to increasing of part of common species on Northern and Southern Ural. The species composition differences slightly increase in case of high percentage cover J. sibirica in northern and southern mountain tundra communities. Работа выполнена при поддержке проектов № 16–05–00454 «Современная экспансия можжевельника сибирского (Juniperus sibirica Burgsd.) в горные тундры, луга и редколесья на Южном и Северном Урале» и № 15–29–02449 «Климатогенные изменения структуры и биоразнообразия высокогорной растительности в южной части Уральских гор в последнем столетье».

In this work, the authors estimate the species abundance and the characteristics of ground cover (herb-dwarf-shrub and moss-lichen layers) structure in mountain tundra communities. They study mountain tundra communities that have significant differences in the degree of Juniperus sibirica Burgsd cover. Species richness and the abundance of plants were estimated on 40 plots (10x10 m) in mountain tundra communities of the Northern (the Kvarkush ridge) and Southern (the Zigalga and Nurgush ridges) Urals. Study plots were chosen with different degree of J. sibirica coverage, from lack of cover to dominance: the groups were 0%, 30–40% and 80–95%. J. sibirica invasion of mountain tundra communities in the Northern and Southern Urals has led to a decrease in the abundance of herbs and mosses on plots dominated by J. sibirica. The authors could not reveal other changes in the mountain tundra structure caused by the J. sibirica invasion. The α-biodiversity of plants and lichens and the ratio of functional and ecological plant groups do not depend on the degree of J. sibirica cover. Field work was developed with the financial support of the Russian Foundation for Basic Research (grant №№ 15-29-02449 and 16-05-00454) and data analysis was completed with the Russian Federal Government's financial support to the Institute of Plant and Animal Ecology UD RAS