The spatial and temporal dynamics of forest-tundra communities was studied on the Yamal Peninsula within the northern treeline ecotone. The paper presents the results of surveying 12 sample plots and more than 1000 trees of Siberian larch and Siberian spruce. Based on cross-dated tree-ring chronologies, the age structure and dynamics of stands for the last 150 years were obtained. Dynamic processes in stands of the northern treeline ecotone are most pronounced in the sparse forests, where there has been a sharp increase in stand density since the middle of the 20th century. Correlation analysis of tree establishment time with instrumental observations of climatic variables showed that the establishment of new larch and spruce individuals in different stand types is significantly influenced by the amount of precipitation in June-August.