Yixing Zhao Xin Qie ^*

• Hebei bureau of geology and mineral resources exploration, Shijiazhuang，Hebei, China

As an important part of terrestrial ecosystem, vegetation plays a vital role in the terrestrial carbon cycle. As one of China's three major urban clusters, the Beijing-Tianjin-Hebei region has experienced significant changes in vegetation due to climate change and large-scale ecological restoration efforts. Climate change and human activities are two factors that have important effects on the carbon cycles of terrestrial ecosystems． Quantitative assessment of the relative effects of climate change and human activities on vegetation dynamics is of paramount importance for regional sustainable development and ecological security. In this study, based on ground meteorological data and remote sensing data including NDVI, an improved CASA model was employed to estimate the net primary productivity (NPP) of vegetation in the Beijing-Tianjin-Hebei region from 2000 to 2020. Utilizing methods such as trend analysis, Mann-Kendall significance test, and correlation analysis, we investigated the spatiotemporal patterns of vegetation NPP and its correlations with precipitation, temperature, and solar radiation. Furthermore, the partial derivative trend residuals method was adopted to separate and quantify the impacts of climate change and human activities on vegetation NPP in different years. The results show that: (1) from 2000 to 2020, the overall trend of vegetation NPP in the Beijing-Tianjin-Hebei region exhibited an increasing trend, with a spatial distribution pattern showing a step-like distribution from low to high to low from northwest to southeast. The multi-year average NPP was 384.90 g C m -2 , with an annual average growth rate of 3.00 g C m -2 . The NPP values of different vegetation types from large to small were: forests (578.40 g C m -2 ), shrubland (386.57 g C m -2 ), grassland (380.17 g C m -2 ), and cropland (324.91 g C m -2 ). ( 2) The proportion of regions with a positive correlation coefficient between average temperature and vegetation NPP in the Beijing-Tianjin-Hebei region from 2000 to 2020 was 69.85%, while the proportions of regions with positive correlations between precipitation and solar radiation with vegetation NPP were 92.1% and 89.19%, respectively.