[Quantitative Analysis of the Drivers of the Spatio-temporal Evolution of Vegetation NPP in the Beijing-Tianjin-Hebei Ecological Barrier Area].

The Taihangshan-Yanshan Region is an important ecological barrier area in Beijing-Tianjin-Hebei, and it is of great importance to investigate the spatial distribution pattern and driving mechanism of net primary productivity （NPP） of vegetation for ecological restoration. The MOD17A3HGF.061 NPP dataset was obtained using the Google earth engine（GEE）, and Sen trend, coefficient of variation, partial correlation, complex correlation, and residual analysis were applied to investigate the spatial and temporal patterns of vegetation NPP in the study area and to quantitatively isolate the relative contributions of climate change and human activities. The results showed that： ① The vegetation NPP in the study area showed an overall increasing trend from 2003 to 2021, with a rate of（C-based）2.57 g·（m·a） and the distribution characteristics of "low in the surroundings and high in the middle" in the Taihangshan area, "high in the north and low in the south" in the Yanshan area, and "low in the north and low in the south" in the Yanshan area. At the same time, the spatial distribution characteristics of "low around and high in the middle" in the Taihangshan area and "high in the north and low in the south" in the Yanshan area were shown. Nearly 70% of the regions had medium or low volatility of vegetation NPP, and 80% of the regions had the opposite trend of future changes. ② The vast majority of NPP changes were positively correlated with precipitation and negatively correlated with temperature, but the significance was not strong； only 23% of the area had a strong correlation between vegetation NPP changes and meteorological factors, and it was concentrated in the central Yanshan Mountains, while the rest of the area was mainly driven by reasons other than climatic factors. ③ Potentially improved （NPP>0） and potentially degraded （NPP<0） areas were roughly equally distributed, but human activities played a positive role in most of the areas （79%）； 76% of the areas were dominated by human activities in the actual improved areas and 58% in the actual degraded areas, and human activities were the main factor dominating the NPP succession of vegetation in the study area. The results of this study provide an important reference for the formulation of precise vegetation ecological protection and restoration policies in the Beijing-Tianjin-Hebei ecological barrier area.