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.

A study by researchers from the Institute of Earth Environment of the Chinese Academy of Sciences (IEECAS) has revealed the altitudinal difference of growth-climate response models in the north subtropical forests of China.

Their findings were published in Dendrochronologia on Jan. 21.

The researchers investigated the climatic response of the radial growth (tree ring) of Pinus henryi Mast. from different altitudes of Shiyan, the northern subtropical China. 

They 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 leading to the change of climatic response models along altitude gradient.

The 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.

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.

This work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences, the National Natural Science Foundation of China, the Second Tibetan Plateau Scientific Expedition and Research and the State Key Laboratory of Loess and Quaternary Geology Foundation.