The Influence of Climatic Factors on Tree-Ring Width of Siberian Larch in the Upper Basin of the Irtysh River

This paper presents the results of assessing the influence of the main climatic factors on the tree-ring width of Siberian larch (Larix sibirica Ledeb.) growing in the upper basin of the Irtysh River. Tree core sampling was carried out on the northern macroslopes of the Sarymsakty, Tarbagatai and Southern Altai ranges in Kazakhstan, as well as on the southern macroslopes of the Southern Altai ranges in Kazakhstan and China, from three sites on the upper tree line and four on the lower tree line. According to the results of dendrochronological analysis, two generalized tree-ring chronologies, IRTv and IRTn, were obtained, reflecting the variability of the radial growth of Siberian larch in the region of study on the upper and lower tree lines, respectively. On the upper tree line, the radial growth of Siberian larch is dependent on the thermal regime of the beginning of the growing season (June–July). The analysis of tree-ring growth dynamics showed that during 1850–1873, 1881–1900, 1906–1939, 1957–1965 and 1982–1990, tree-ring growth at the upper tree line was characterized by lower values. Since 1850 there has been a positive trend in the tree-ring growth variability, which indicates better thermal conditions since the end of the Little Ice Age. The sufficiently strong climatic signal (r = 0.7) makes it possible to use IRTv chronology for temperature reconstruction. On the lower tree line the variability of radial tree-ring growth is determined by the dynamics of precipitation in the winter-spring-summer period (December–July). The most important aspect of this is moisturization during the completion of snowmelt and the beginning of the growing season (May–June). Analysis of tree growth dynamics showed that over the past 150 years the moisture regime has not changed significantly. The reduced values of tree-ring growth correspond to 1850–1859, 1877–1907, 1916–1936, 1944–1951, 1962–1968 and 1973–1992.This study was supported by the Russian Science Foundation, research project No 17-77-10041