[Response of Branch Attributes of to Climate Variables]

We established a mixed-effects model incorporating climatic factors for the base diameter and length of the primary branches of using stepwise regression, based on climatic data from a total of 40 standard plots located in Xiaolongshan, Gansu Province, Changlinggang Forest Farm in Jianshi County, Hubei Province, and Dagujia Forest Farm in Qingyuan County, Liaoning Province, as well as the data from 120 sample trees. Additionally, we created prediction charts for the fixed effects portion of the optimal mixed model to determine the relationship between climatic factors and base diameter and branch length, to explore the differential response of branches to climatic variables. The results showed that the base diameter mixing model with annual mean temperature and water vapor deficit and the branch length mixing model with annual mean temperature had the best fitting effect, with of 0.6152 and 0.6823, respectively. Based on the fixed effects prediction chart of the mixed model, the overall basal diameter showed an increasing trend with the increases of relative branch depth. The average basal diameter size was in an order of young-aged plantation<middle-aged plantation<near mature plantation<mature plantation. The lower the annual mean temperature, the larger the base diameter and length. The larger the water vapor deficit value, the smaller the base diameter of the branches. Branch length was more sensitive to temperature compared with base diameter. In different developmental stages, the base diameter and branch length of mature plantation were the most sensitive to temperature, while the young plantation was the weakest. Among the rank trees, the base diameter and branch length of the dominant trees were the most sensitive to temperature, while the inferior trees were the weakest. Mixed effect model was more practical in tree modeling. Temperature and precipitation could affect the growth of . would grow well in the environment with low temperature and high humidity.