Quantitative assessment of vegetation carbon sequestration in typical natural secondary forests of the Loess Plateau: Incorporating the influences of human activities and climate variations

The Ziwuling region, the biggest surviving natural secondary forest area on the Loess Plateau (LP), is essential to controlling the climate and preserving the ecological balance of western China. To accurately capture the spatiotemporal dynamics of vegetation carbon sequestration and the impacts of climate change and human activities in the Ziwuling region, this study proposes an improved CASA model-based framework for estimating vegetation carbon sequestration capacity. By estimating vegetation net primary productivity (NPP) from 2001 to 2021 and calculating the weight of vegetation carbon sequestration (W_C), the study employs a combination of statistical methods to analyze the spatiotemporal variation characteristics and driving factors. Our study results show that: (1) From 2001 to 2021, the vegetation W_C in the Ziwuling region increased significantly, the annual average W_C increased from 903.77 g/m²a in 2001 to 1185.35 g/m²a in 2021, reflecting a growth of approximately 31.1 %; (2) In the future, there is a possibility of a decrease in vegetation W_C in the northern region, which accounts for approximately 59.2 % of the study area, while the central region may remain relatively stable; (3) In the Ziwuling region, human activities (HA) have greater influence on vegetation W_C than climate variations (CV) do in most places,and the increase in W_C in 88.7 % of the study area is attributed to human activities. The research findings contribute to understanding the vegetation carbon sequestration response mechanisms in natural forest areas under China's ecological engineering initiatives. Additionally, they provide recommendations for vegetation protection in the Ziwuling region and ecological restoration of the Loess Plateau.