Abstract:

A decline in tree growth has occurred in numerous regions over recent decades and is associated with enhanced water deficits driven by climate warming. This phenomenon may be more noticeable at lower latitudes with higher temperatures. However, the process by which these elevated temperatures alter growth performance is not well understood. In this study, by combining tree-ring data (including 340 increment cores) and remotely sensed vegetation index data, we investigated the long-term growth performance of Pinus sylvestris var. mongolica Litv. (Mongolian pine), an important species for afforestation in northern China, in response to environmental factors in an area of introduction (lower latitude) and its native range (higher latitude). More notable decreases in both tree-ring width index (RWI) and basal area increment at breast height coincided with lower values and larger variations in the satellite-derived vegetation index in the area of introduction. The RWI showed stronger negative correlations with temperature and positive correlations with the self-calibrating Palmer drought severity index during most months in the introduction area. These results indicate that enhanced drought stress caused by elevated temperatures in lower latitudes might be a key factor for the growth decline in Mongolian pine plantations. The negative impact of increased temperatures on tree growth through exacerbating drought stress at lower latitudes with water deficit highlights the need to reduce water stress in forest management in such areas under climate warming-driven aridification.

Key words: Climate warming, Growth decline, Remote sensing, Shelter forest, Tree-ring analysis