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.