Modelling branch growth of Korean pine plantations based on stand conditions and climatic factors

Abstract

To investigate the effects of stand conditions and climatic factors on branch growth and the dynamics of branch growth over time, we constructed a mixed-effects model on branch annual length growth using data from 803 branches of 70 sample trees in Korean pine (Pinus koraiensis Sieb. et al. Zucc.) plantations in Heilongjiang Province, China. The results showed that the introduction of branch age, branch depth into crown, branch diameter with bark, height-diameter ratio of the tree, stand average diameter at breast height, summer mean temperature and summer precipitation significantly improve the model fitting effect. The increase in summer mean temperature promoted branch growth, while the increase in the branch depth into the crown, height-diameter ratio of the tree, stand average diameter at breast height, and summer precipitation negatively impacted branch growth. We found that in the second year, the annual length growth reached a maximum, decreased with increasing branch age and stabilized when the branch age was greater than 20. Younger branches responded more strongly to competitive changes. The influence of summer precipitation on branch growth was greater than that of summer mean temperature. Moreover we found that within the appropriate range, climatic factors will not have a significant impact on branch growth until the summer mean temperature is lower than 16 °C and the summer precipitation exceeds 400 mm, which will have a significant inhibitory effect on branch growth. The introduction of random effects significantly improved the predictive ability of the model, and it was reasonable to select 6 branch annual length growths per branch to estimate random parameters. Our research indicated that branch growth is influenced by the combined effects of climate and competition, which helps to make reasonable forest management decisions under global climate change.