Altitudinal difference increases the complexity of the response of tree growth to climate change in the mountainous areas, and may change the carbon sequestration capacity of forests under the ongoing warming climate. However, researches on the tree growth- climatic relationship at different altitudes in the subtropical regions of China are not in-depth.

Recently, a research group from the Institute of Earth Environment of the Chinese Academy of Sciences (IEECAS) investigated the climatic response of the radial growth (tree ring) of Pinus henryi Mast. from different altitudes of Shiyan, subtropical China, and found the existence of a temperature-related altitudinal threshold (TRAT) between 1070-1330 m a.s.l. The hydro-thermal combination models above and below the TRAT may be significantly different, thus lead to the change of climatic response models along altitude gradient.

The study was published in Dendrochronologia on January 21.

In this study, researchers found that tree growth-climate response models can be divided into two types according to the altitudinal gradient: the high-altitude model above TRAT (>1330 m a.s.l.) and the low-altitude model below TRAT (<1070 m a.s.l). The biggest difference between the two models is that tree growth at the low altitudes shows significantly negative response to temperature in the previous September–December and current April–May, while positive response to moisture conditions from the previous September to current May, April–May in particular; while the high-altitude ones show consistently positive responses to temperature in current February–April, but no significant response to seasonal moisture condition. Moving correlation analysis revealed that the relationships between tree growth and the limiting climatic factors also presented evident altitudinal difference: gradually strengthened at the high altitudes but weakened at the low altitudes. It is distinct that water availability and demand are critical for the growth of low-altitude trees, and high-altitude trees show a stronger positive response to climate warming, therefore could be an important carbon sink in the future. In addition, future forest management should focus on the low altitudes and formulate effective protection strategies.

This work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (XDB40010300), the National Natural Science Foundation of China (41671212), the 2nd Tibetan Plateau Scientific Expedition and Research (2019QZKK0101) and the State Key Laboratory of Loess and Quaternary Geology foundation.

Contact: Bai Jie, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China. Email: baijie@ieecas.cn