Expansion of Juniperus sibirica Burgsd. as a response to climate change and associated effect on mountain tundra vegetation in the Northern Urals

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 20^th 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°С 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.