Differences in NPP drivers and response mechanisms in typical subtropical mountain ecosystems in China

Abstract Mountain ecosystems (ME) have experienced significant anthropogenic disturbances, resulting in severe degradation. Due to their intricate topography, climatic zonation, and spatial heterogeneity, the spatial and temporal evolution of net productivity in ME, and the underlying driving mechanisms remain unclear. This study focuses on the Southern Hilly Mountainous Belt of China (SHMB) to investigate the trends in net primary productivity (NPP) and its response mechanism from 2001 to 2020. The study employs various quantitative methods such as Theil-Sen slope estimator, Mann-Kendall trend test, Convergent Cross Mapping (CCM) analysis, Granger Causality analysis, and Geographical Detectors. The findings of this study are as follows: (1) CCM analysis is deemed suitable for monitoring the causal relationship between climate factors and NPP. (2) NPP exhibits a significant decreasing trend in the eastern and central regions of SHMB while showing a notable increase in the northwestern region. The southwestern region demonstrates a declining trend due to warming and drying effects. (3) NPP is slightly lower on sunny slopes compared to shady slopes. Human activities significantly impact vegetation at lower altitudes by altering forest stand structures which affects carbon sequestration capacity. Vegetation at higher altitudes is primarily influenced by precipitation with temperature playing a lesser direct role. In conclusion, climatic factors exert limited influence on NPP at lower altitudes underscoring the importance of regional governments' efforts towards improving ecological environment through effective forest management practices. These findings contribute to an enhanced understanding of the carbon cycle process crucial for achieving carbon neutrality, enhancing ecological functions, and studying global change.