Abstract
Changes in vegetation net primary productivity (NPP) are primarily influenced by climate change and human activities, but understanding the dominant factors and their contributions at different time stages remains unclear. Here, we developed a method to quantify the relative contributions of climate and human factors to vegetation NPP in China over the past 40 years, using three types of NPP based on multi-source data sets - actual NPP (aNPP), potential NPP (pNPP) and human occupied NPP (hNPP). The results revealed a strong correlation (R2 = 0.7629, p < 0.001) between the estimated values of the Carnegie-Ames-Stanford Approach (CASA) model and the measured values. The results showed that from 1982 to 2000, the annual average aNPP in China was 501.0 g C/m² with a sum annual aNPP of 378.2 Tg C. From 2001 to 2020, the annual average aNPP increased to 517.1 g C/m² with a sum annual aNPP of 391.1 Tg C. The increase or decrease in aNPP from 1982 to 2000 was primarily influenced by human activities, with contribution rates of 34.26% and 50.43%, respectively. From 2001 to 2020, climate became the dominant factor in the increase of aNPP (contribution rate of 43.90%), while human activities became the dominant factor in the decrease of aNPP (contribution rate of 83.75%). The study also revealed a significant positive correlation between aNPP and precipitation, temperature, and gross domestic product (GDP), as well as a negative correlation with population density. Overall, the upward trend of climate-dominated aNPP is gradually increasing (12.24–43.90%), while the downward trend of human-dominated aNPP is also gradually increasing (50.43–83.75%). This study is benefit to a comprehensive understanding of the driving forces of vegetation aNPP changes, and provide scientific strategies for vegetation adaptation to climate warming.