Abstract: [Objective] Study of the effects of thinning and climate factors on the variation of tree ring width will help further deepen our understanding of the factors driving Larix olgensis tree ring width during climatic change.[Method] In this study, radial width profiles from breast height of L. olgensis trees were analyzed using a nonlinear mixed modeling approach. Radial width profiles were sampled from 20 permanent plots (surveyed from 1987 to 2012) in northeast China within semi-natural larch-spruce-fir forests in which thinning was conducted. Each ring width was measured by Lintab 6 tree-ring width measuring instrument before cross dated by the COFECHA software, a total of 231 radial width profiles were used for modeling. The climate data was linearly interpolated from the data of neighboring weather stations since 1964 to 2010. Combining the overlapping periods of each part of the data, the data selected from 1987 to 2010 were used for modeling.[Result] The results showed that cambial age, stand density, competition, thinning and climatic factors had significant effects on tree-ring width of L. olgensis. Thinning was applied on the plots twice in 1987 and 1993, respectively. The first thinning was carried out at stand age of 20, we found that the positive effect of heavy thinning (40%) was stronger than that of the moderate thinning (30%) on ring width, while light thinning (20%) was found not significant. After the first thinning, the growth rate of ring width was accelerated which lasted 4 years and reached its peak at the 2^nd-3^rd year. For the second thinning, only moderate and light thinning intensity were adopted, the effects of both were found to be significant on ring width. However, the positive effect of the light thinning was identified stronger than moderate thinning on ring width. Similarly, the growth rate of ring width was accelerated after second thinning which lasted 15 years and reached its peak at the 4^th-5^th year. Seven climatic factors were found to be directly related to ring width. Varied effects of the climatic factors were found on ring width, the greatest effect was found of the highest temperature in July and the accumulative temperature higher than 5℃ in growing season. The summer hot and humid index was shown less impact, while minimum but significant effects were found in winter precipitation, the lowest temperature in September, the average temperature in April and precipitation in May. The determination coefficient of model was significantly improved from 0.37 to 0.73 by introducing a random effect of model intercept at the plot and the individual levels.[Conclusion]The heavy and moderate thinning can significantly improve the growth of L. olgensis in mixed stands within 4 years following the thinning. Significant climatic effects were identified on the growth of L. olgensis at low-altitudes of northeast China. The highest temperature in July and accumulative temperature higher than 5℃ in growing season were found to be the main limiting factors on the growth. Our results indicate that the climatic effects should be considered in order to accurately model the growth of L. olgensis under current climate scenario.

Key words: tree-ring width, thinning, climate, Larix olgensis, nonlinear mixed effect model