Analysis of the age structure of Dahurian larch (Larix gmelinii Rupr.) forests in the western part of the Putorana Plateau (Sukhie Gory Range) and comparison of diachronous topographic maps and satellite images have revealed changes in the altitudinal position of the upper boundary of tree vegetation. the most significant changes occurred on south- and southwest-facing slopes. Correlations of trunk diameters with the phytomass of trees and its fractions have been found. the course of changes in the structure and phytomass of tree stands in the upper timberline over the past centuries has been reconstructed. Forest expansion has been facilitated by the general change in climate conditions (warming) in the study area. This study was supported by the Russian Science Foundation, project no. 17-14-01112.