| Summary: | Changes in the altitudinal position of the timberline in high mountain areas of the Nether-Polar Urals and basic factors that influence such changes have been revealed on the basis of comparison of the age structure of Siberian larch (Larix sibirica) and arctic birch (Betula tortuosa) tree stands and photographs made in different years. On the mountain slopes studied, an upward shift of the timberline took place in areas covered in winter with thick snow (in the late 18th century), with Siberian larch being the pioneer species. Larch began colonizing areas with a thin snow cover in the 20th century. Birch appeared later and has since strengthened its positions. The increase in winter temperatures and precipitation facilitated the expansion of the forest. © 2013 Pleiades Publishing, Ltd. ACKNOWLEGMENTS This study was supported by the Russian Foundation for Basic Research, project nos. 08 04 00208 and 11 04 00623, and the Ural Branch of the Russian Academy of Sciences, program no. 12 С 1038.
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