Effects Of Thinning And Climate Factors On Larix Olgensis Tree-ring Width

Disentangling thinning and climate factors on the variation of tree-ring width will help further our understanding of the factors driving Larix olgensis tree-ring width during climatic change.In this study,radial width profiles from breast height of Larix olgensis trees were analyzed using a nonlinear mixed modeling approach.Combining with sample plot survey data and climate data,we build the tree-ring width model with the thinning effect,the tree-ring width model with climate and thinning effects,and the climate-sensitive tree-ring width models in the stands of different thinning intensities were used to analyze the effects of thinning and climatic factors on tree growth and the effects of thinning on the relationship of tree growth and climatic factors.The main conclusions are as follows:(1)After introducing the random effects of plot level and individual tree level into the model,the AIC value of the model decreases,and the coefficient of determination(R2)increases significantly.The mixed effect model can improve the prediction accuracy and explain the source of random error,so it is an ideal research method to study the growth of trees.(2)Cambial age,stand density,single tree competition,thinning and climatic factors all have a significant effect on tree-ring width of Larix olgensis.After thinning,the tree-ring width increases,and it shows the trend of increasing first and then weakening.The first thinning was taken at the time of about 20 years old.The effect of heavy thinning(40%)is stronger than which of moderate thinning(30%),wheal the effect of moderate thinning is stronger than which of light thinning(20%).The second thinning was taken when the forest at about 26 years old,and the effect of moderate thinning is weaker than which of light thinning.Therefore,the moderate and heavy thinning of mixed forests of Larix olgensis and spruce,at the age about 20 years old,can significantly improve the growth of preserved wood in the following few years.(3)Seven of the climatic factors have significant effects on the ring width of Larix olgensis.Among them,the highest temperature in July and the accumulated temperature higher than 5? in the growing season shows the greatest impact,followed by the summer heat and moisture index,and the winter precipitation,he lowest temperature in September,the average temperature in April and May precipitation have little effect on tree-ring width.In the context of global climate change,when studying the growth of trees,in order to make the research more accurate,the influence of climatic factors should be taken into account.(4)The climatic factors affecting tree-ring width are slightly different in the forests with different thinning intensities.Winter precipitation shows a significant effect in the non-trimmer group and the light thinning group,but not in the moderate and heavey thinning group.Moderate and heavy thinning can change the influence of climatic factors on Larix olgensis tree-ring width,so that winter precipitation will no longer affect the growth of Larix olgensis,and enhance the effect of accumulated temperature on the growth of Larix olgensis.Therefore,thinning can be used as an important means of safeguarding forest productivity in temperate forest to resist climate change.