黄河流域草地净初级生产力时空动态及其驱动机制

黄河流域是生态系统的敏感区,流域草地生态系统在气候变化和人类活动驱动下发生了显著变化。基于多源遥感影像和气象站点资料等,采用改进后的CASA模型估算2001—2018年黄河流域草地净初级生产力(NPP),评估定量反演结果精度,分析研究时段内流域草地净初级生产力时空动态,探讨气候要素和人类活动对流域草地净初级生产力的影响。结果表明：1)基于改进的CASA模型能够高精度模拟黄河流域草地NPP。2)2001—2018年黄河流域草地NPP呈增加趋势,且在2013年发生突变。2001—2013年气候和人类活动均促进流域草地NPP增加,而2013年后人类活动抑制流域草地NPP增加的作用明显增强,抑制区域面积较前一阶段增加34.89%。整体上,人类活动对草地NPP的影响强度低于气候要素影响强度。3)耕地和建设用地面积的变化,是驱动实际净初级生产力动态的重要人类活动要素。耕地和建设用地面积的增加与草地面积减少、实际净初级生产力增加速率的降低紧密相关。伴随经济发展,应坚持实施退耕还林还草政策,并加强对草地生态保护的监督。

Spatiotemporal dynamics of grassland net primary productivity and its driving mechanisms in the Yellow River Basin

The Yellow River Basin (YRB) is a sensitive area for ecosystems. The grassland ecosystem in the YRB has changed significantly under climate change and human activities. Combing with multi-source remote sensing images and meteorological site data, we estimated the grassland net primary productivity (NPP) in the Yellow River Basin from 2001 to 2018 using the improved CASA model in this paper. After quantitatively evaluating the accuracy of simulated NPP data, we analyzed the spatiotemporal dynamics of grassland NPP and its responses to climate changes and human activities in the YRB. Results showed that 1) the improved CASA-based model could simulate the grassland NPP in the Yellow River Basin with high precision. 2) Grassland NPP in the YRB showed an increasing trend from 2001 to 2018, with a sudden change in 2013. Climate and human activities contributed to the increase of grassland NPP from 2001 to 2013. After 2013, the effect of human activities inhibiting the increase of grassland NPP increased significantly, and the area of the inhibited area increased by 34.89% over the previous period. Overall, the influence intensity of human activities on grassland NPP was lower than that of climate factors. 3) Change of cropland and built-up land area was the important human activity that drove the dynamics of actual NPP. The increase of cropland and built-up land closely related to the decrease of grassland area and the reduction of increase rate of actual NPP. With the development of the economy, the "Grain for Green" program should be persistently implemented, and the supervision of grassland ecological protection should be strengthened.