Climate warming induced pervasive growth decline in Chinese pine populations of the Loess Plateau, China.

Modern warming and associated aridification have intensified forest growth decline and tree mortality, weakening forest carbon sequestration. This study aims to investigate how Chinese pine (Pinus tabuliformis Carr.) responds to these climatic shifts across the Loess Plateau, a region highly sensitive to environmental changes. We synthesized tree-ring width chronologies from 60 sites spanning major geomorphological units of the Loess Plateau. To evaluate the impact of rapid warming, we compared climate-growth relationships between two distinct periods: the pre-warming phase (1901-1960) and the post-warming phase (1961-2012). Before 1960, when warming and drying were not pronounced, radial growth generally increased across regions, primarily limited by moisture while temperature had a modest stimulatory effect. After 1960, as warming and aridification strengthened, growth declined across all geomorphological units. Moisture limitation intensified, and higher temperatures shifted from a weak benefit to a clear suppressive influence. Spatially, the southern Loess Plateau showed the highest sensitivity to both growing- and non-growing-season climate, while the western and eastern regions were less sensitive and primarily influenced by non-growing-season conditions. The spatially heterogeneous responses identified in this tree-ring dataset underscore the complex impact of recent warm-dry trends on forest ecosystems. These findings are crucial for improving our understanding of forest dynamics in semi-arid regions and can guide adaptive forest management strategies to sustain ecosystem functioning under ongoing aridification of the Loess Plateau.