Spatiotemporal dynamics and quantitative attribution of vegetation net primary productivity in China: climate change contributes more than human activities

Vegetation net primary productivity (NPP) is a key indicator of ecosystem carbon sequestration capacity and ecological quality. The spatiotemporal dynamics of vegetation NPP in China, its nonlinear responses to multidimensional driving factors, and the relative contributions of climate change and human activities to NPP variation were quantitatively examined. Vegetation NPP in China from 2001 to 2022 was analyzed using the MOD17A3HGF dataset, together with Theil-Sen trend analysis and the Mann-Kendall test, and the heterogeneous dynamics of NPP between natural forests and planted forests were further compared. To overcome the limitations of conventional linear models in capturing nonlinear interactions, an XGBoost-SHAP framework combined with nonlinear residual analysis was employed to quantify the effects of climatic and anthropogenic factors on NPP. The results indicated that: (1) From 2001 to 2022, vegetation NPP in China exhibited a distinct spatial pattern of high values in the southeast and low values in the northwest, together with an overall increasing trend at an average rate of 2.82 gC·m⁻²·a⁻¹ and pronounced interannual fluctuations. The spatial pattern displayed extremely strong positive spatial autocorrelation (Moran’s I > 0.91), forming a stable clustering pattern characterized by high values in the south and low values in the north. Hurst exponent overlay analysis further indicated that approximately 51.36% of the study area may face a risk of trend reversal from increase to decrease. (2) Between 2005 and 2020, the proportion of planted forest area increased from 6.10% to 9.51%, and planted forests consistently exhibited higher annual mean NPP than natural forests, indicating strong short-term carbon sequestration benefits. (3) Land cover was the dominant factor controlling NPP differentiation. Among climatic factors, precipitation and temperature exerted strong positive effects on productivity, whereas vapor pressure deficit showed a significant inhibitory effect. Among anthropogenic factors, economic development promoted vegetation growth, while intensive human footprint imposed clear negative pressure. (4) In 55.15% of China, vegetation carbon sequestration capacity increased under the joint effects of climate change and human activities. In areas with increasing NPP, the mean relative contributions of climate change and human activities were 66.48% and 33.52%, respectively, whereas in areas with decreasing NPP, the corresponding values were 53.67% and 46.33%, respectively.