Altitudinal difference of growth-climate response models in the north subtropical forests of China

Abstract

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. In this work, four tree-ring width chronologies from Pinus henryi Mast. growing at different altitudes of Shiyan, the northern subtropical China were developed. Results of Pearson correlation analysis, factor analysis and redundancy analysis indicate that tree growth-climate response models can be divided into two types according to the altitudinal gradient: the high-altitude model, represented by SWDH and WDSH above 1330 m a.s.l., and the low-altitude model, represented by WDSL and DDZL less than 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, and 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. The existence of a temperature-related altitudinal threshold between 1070 m a.s.l. to 1330 m a.s.l. may change the hydro-thermal combination models above and below the threshold, thus lead to the change of climatic response models along altitude gradient. 30-yr moving correlation analysis reveals that the relationships between tree growth and the limiting climatic factors present 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.