Presented are the results from investigating the periglacial zone of the Munku-Sardyk massif in Eastern Sayan. Dendrochronometry data are used in analyzing the cyclicity of natural processes that manifests itself in increment in trees growing in extreme conditions. The analysis revealed secular and intrasecular cycles. A correlation of increments in larch and Siberian stone pine with changes in summer temperatures (the correlati on coefficients 0.56 and 0.48, respectively) is observed. For the period of observation of the Peretolchin glacier (1900–2015), the stages of its retreat (1900–1965 and 1983–2000) and advance (1965–1983) were revealed, which influenced the changes in increment in trees and the degree of accumulation of bottom sediments in the proglacial Lake Ekhoi. A comparison of the character of growth of a “fossil” tree in the Holocene optimum with present-day long-lived trees shows a higher sensitivity of the ancient tree (the coefficient 0.43) and a lower sensitivity in present-day trees (0.32 for larch, and 0.26 for Siberian stone pine). Thermochronometry data were used to determine a decrease in air temperature with height in June (an optimal month for increments in trees) to 0,468 °C/100 m.Keywords: geosystems, dendrochronological analysis, correlation, cycles, glacier, climate change.