Abstract：
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.
摘要：
自2012年以来，“山体开挖与城市建设”（MECC）项目已在中国黄土高原广泛实施，通过平整黄土山顶以填充山谷，将沟渠转变为平坦的土地，以进行城市扩张。然而,这种前所未有的人类活动对其未知的潜在生态影响引起了广泛的争议。定量评估MECC项目对植被的影响是生态管理和恢复的关键。以黄土高原最大的MECC项目区为例，延安新区（YND），作为研究区域，本研究利用2009年至2023年的多时相归一化差异植被指数（NDVI）时间序列，调查了MECC项目实施前后植被动态的时空格局，并探讨了植被动态对大规模MECC项目的响应。结果表明，由于MECC项目，YND的植被动态表现出显著的时空异质性，受项目影响地区的植被破坏迅速，恢复缓慢。植被破坏仅发生在项目影响区域,其中84%的地区在10年内开始复苏，表明大规模MECC项目对区域植被的影响有限。植被动态与MECC项目具有很强的相关性,说明项目影响区植被的破坏和恢复主要受人为控制,这突出了有针对性的生态政策的重要性。具体来说,MECC项目在土地创建期间对植物种群结构造成了局部人为破坏，但是通过城市化实现了植被的再生和合理配置，逐步形成新的平衡生态环境。这些发现将有助于全面了解植被对此类大规模工程活动的反应，并帮助地方政府采取促进植被恢复的项目或政策。
