Since 2012, the Mountain Excavation and City Construction (MECC) project has been implemented extensively on the Loess Plateau of China, transforming gullies into flat land for urban sprawl by leveling loess hilltops to fill in valleys. However, this unprecedented human activity has caused widespread controversy over its unknown potential ecological impacts. Quantitative assessment of the impacts of the MECC project on the vegetation is key to ecological management and restoration. Taking the largest MECC project area on the Loess Plateau, Yan'an New District (YND), as the study area, this study investigated the spatiotemporal pattern of vegetation dynamics before and after the implementation of the MECC project using a multitemporal normalized difference vegetation index (NDVI) time series from 2009 to 2023 and explored the response of vegetation dynamics to the large-scale MECC project. The results showed that the vegetation dynamics in the YND exhibited significant spatial and temporal heterogeneity due to the MECC project, with the vegetation in the project-affected areas showing rapid damage followed by slow recovery. Vegetation damage occurred only in the project-affected area, and 84 % of these areas began recovery within 10 years, indicating the limited impact of the large-scale MECC project on the regional vegetation. The strong correlation between vegetation dynamics and the MECC project suggested that the destruction and recovery of vegetation in the project -affected areas was mainly under anthropogenic control, which highlights the importance of targeted ecological policies. Specifically, the MECC project induced local anthropogenic damage to the plant population structure during the land creation period, but regeneration and rational allocation of the vegetation were achieved through urbanization, gradually forming a new balanced ecological environment. These findings will contribute to a full understanding of the response of vegetation to such large-scale engineering activities and help local governments adopt projects or policies that facilitate vegetation recovery.

Mountain excavation and city construction (MECC) projects being launched in the Loess Plateau in China involve the creation of large-scale artificial land. Understanding the subsurface evolution characteristics of the artificial land is essential, yet challenging. Here, we use an improved fiber-optic monitoring system for its subsurface multi-physical characterization. The system enables us to gather spatiotemporal distribution of various parameters, including strata deformation, temperature, and moisture. Yan'an New District was selected as a case study to conduct refined in-situ monitoring through a 77 m-deep borehole and a 30 m-long trench. Findings reveal that the ground settlement involves both the deformation of the filling loess and the underlying intact loess. Notably, the filling loess exhibits a stronger creep capability compared to underlying intact loess. The deformation along the profile is unevenly distributed, with a positive correlation with soil moisture. Water accumulation has been observed at the interface between the filling loess and the underlying intact loess, leading to a significant deformation. Moreover, the temperature and moisture in the filling loess have reached a new equilibrium state, with their depths influenced by atmospheric conditions measuring at 31 m and 26 m, respectively. The refined investigation allows us to identify critical layers that matter the sustainable development of newly created urban areas, and provide improved insights into the evolution mechanisms of land creation. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).