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Features of Radial Growth Rate of Trees in Agro-Pastoral Transition Zone, Northern China

The Vaganov–Shashkin process-based model was used to explore the variation characteristic of the radial growth rate of Pinus tabulaeformis in the agro-pastoral transition zone in northern China. The tree-ring width chronologies of the four sampling sites were significantly positively correlated with the simulated series (p < 0.01), and the simulated onset and end dates of tree radial growth indicated that April to October was the main growing season. Temperature affects the radial growth rate of tree stems at the start and end of the growing season, while soil moisture availability affects the radial growth rate in the main growing season. Despite the differences in amplitude, the integral growth rate showed a bimodal pattern, which to some extent responded to the hydrothermal configuration of the East Asian summer monsoon climate. Compared with the peak changes in the summer monsoon fringe area in Northwest China, the highest peak of the integral growth rate in this study area appeared around August in the late growing season, reflecting the adaptability of trees to the local climatic environment. The average values of the integral growth rate and rate due to soil moisture, inferred from extreme wide-ring and narrow-ring years, were significantly different (p < 0.01), while the average growth rates due to temperature were not significant (p > 0.05). The analysis results indicate that moisture availability is a key limiting factor for the radial growth of Pinus tabulaeformis. Our study provides valuable knowledge about the growth processes of the main tree species related to the hydroclimatic variables in northern China and offers a new perspective on mitigating the adverse effects of a warmer climate on the forest in the semi-arid region in the future.