Divergent responses to climate factors in the radial growth of Larix sibirica in the eastern Tianshan Mountains, northwest China

The radial growth of Larix sibirica has exhibited divergent responses to temperatures in the growing season due to the temperature-driven drought stress in the eastern Tianshan Mountains of Northwest China. The warming of the continental interior of the Northern Hemisphere in the latter half of the twentieth century has led to divergent responses between trees growth and climate factors at high latitudes. This study explored the variability in the responses of radial growth to climate factors and the temporal stability of growth-climate relationships under climate change for Siberia larch (Larix sibirica Ledeb.) in the mid-latitude area of the eastern Tianshan Mountains. The results indicated as follows: (1) Analysis of the relationships between tree-ring width chronology and climate factors before and after the abrupt increases in temperature demonstrated that divergent responses of radial growth occurred in the eastern Tianshan Mountains, suggesting that correlation coefficients with temperature varied significantly in the growing season. (2) Examination of variations in the climate factors limiting radial growth in the two time periods demonstrated that the minimum temperature played a key role from 1989 to 2012. (3) Assessment of the temporal stability of growth-climate relationships by a moving correlation function demonstrated that the positive sensitivity of Siberia larch to temperature during the growing season decreased. The reasons for this 'divergence problem' were the increased drought stress and changes in the physiological responses of trees. (4) Simulation of the trend of basal area increment by linear regression showed that the growth rate of Siberia larch first increased and then decreased. The future effects of increasing temperature may cause significant alterations in forest ecosystems, with greater effects on forests in arid and semi-arid areas.