土地退化过程、机制与影响——以土地退化与恢复专题评估报告为基础

土地退化已成为威胁32亿人口福祉的全球性重大环境问题之一，近年来受到UN、IPBES、IPCC等组织的广泛关注。然而，当前的土地退化研究中，还存在概念不清、过程和机理不明、影响认识不彻底等问题，因此，厘清土地退化的概念、过程和机制是防止土地退化和恢复退化土地的关键。以生物多样性和生态系统服务政府间科学-政策平台（IPBES）土地退化与恢复专题评估报告为基础，剖析了土地退化的概念、过程、机制及影响：土地退化过程受自然环境和人类活动两大因素驱动，退化过程包括疑似退化、历史退化、敏感退化、弹性退化、持续退化和永久退化6种状态；土地退化类型可根据土地利用类型分为城市土地退化、农田退化、森林与草地退化、湿地退化等；土地退化具有多重影响，包括威胁食物和水安全，影响生物多样性及生态系统服务，引发地区冲突、大规模人口迁徙和疾病传播，加剧贫困及全球气候变化。土地退化过程、机制及影响的审视将为我国沙漠化、石漠化等土地退化的进一步研究提供理论指导，并为我国"山水林田湖草"土地系统的统筹治理和"美丽中国"、"生态文明"建设提供决策支持。

Processes, mechanisms, and impacts of land degradation in the IPBES Thematic Assessment

Land degradation has become one of the major environmental issues that threaten the well-being of the world''s 3.2 billion people. In recent years, it has received extensive attention from the United Nations (UN), the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), the Intergovernmental Panel on Climate Change (IPCC) and so on. However, existing land degradation studies still suffer by unclear concepts, ambiguous processes and mechanisms, and incomplete understanding of impacts. Thus, clarifying the process and mechanism of land degradation is the key to preventing further land degradation and restoring degraded land. Based on the thematic assessment of the IPBES, the present study reviewed the concept, process, mechanisms as well as impacts of land degradation. The process of land degradation is driven by two factors:the natural environment and anthropogenic activities. In land degradation process, there are six land degradation states; namely, the appearance of degradation, degraded in the past, susceptible to degradation, land recovers when stressors are removed, temporal trend of increase in degradation, and stable degraded state. Land degradation can be divided into urban land degradation, cropland degradation, forest and grassland degradation, wetland degradation, and other types of land degradation based on land use types. Land degradation can threaten food and water security, reduce biodiversity and ecosystem services, trigger regional conflicts, mass migration, and disease transmission, exacerbate poverty and global climate change. The review of the land degradation process, mechanism, and impacts will provide theoretical guidance for in-depth study of land degradation, such as desertification and rocky desertification in China, and provide decision support for overall planning of governance of the mountain, water, forest, cropland, lake, and grass systems, supporting the construction of a Beautiful China and Eco-civilization.