Spatial and temporal patterns and driving factors of carbon in green great wall project, Africa

Abstract

Net Primary Production (NPP) is a critical indicator of vegetative growth status, carbon sequestration capacity, and overall terrestrial ecosystem productivity, thereby contributing significantly to global ecological stability. In the Africa Sahel region, as well as the largest ecological project in Africa——The Green Great Wall, characterized by diverse and dynamic ecosystems, the quantification of vegetation degradation and NPP variability remains limited and uncertain. Therefore, this study provides substantiating evidence to support the enhancement and preservation of vegetative ecosystems in the Sahel region by analyzing spatial and temporal variations in NPP and its driving factors from 2001 to 2020. The Theil-Sen median and the Mann-Kendall significance test were employed to evaluate the NPP spatio-temporal patterns, while the geographical detector model was implemented to measure the influence of environmental variables within the Great Green Wall corridor. We found that the NPP exhibited an upward trend, with 121.97 gC m⁻² annual average between 2001 and 2020. Over the past two decades of the Green Great Wall Project, approximately 40 % of the region exhibited an increase in NPP, 7 % experienced a decline, while 53 % remained desert or bare land. Spatially, the highest observed NPP was recorded in Ethiopia at 556.23 gC m⁻² yr⁻¹, while the lowest value observed was in Niger at 0.43 gC m⁻² yr⁻¹. The geographical detector analysis indicated that temperature and precipitation emerged as the dominant climatic driver of NPP variability, while interaction analysis revealed that the combined influence of precipitation and temperature had the strongest effect on NPP dynamics during the study period. Our findings offer regional evidence for evaluating the benefits of forestry ecological projects in arid zones, contributing to enhanced ecological well-being and resilience in Africa, and providing valuable insights for advancing the Sustainable Development Goals.