Methods, progress and prospect for diagnosis of karst ecosystem health in China-An overview

China is the country with the largest area and widest distribution of carbonate karst, with a population of approximately 200 million and an economic scale of approximately 10% of the country. In particular, the southwest region centered in Guizhou, located at the upper reaches of the Yangtze and Pearl Rivers, is an economically underdeveloped but critical ecological security barrier for the country. Karst landforms are important topological features. Scientific diagnosis of the health of its ecosystem is not only essential for ecological restoration and sustainable development but is also the basic premise for formulating response plans. Although a significant amount of research has been carried out in the past, a lack of systematic and holistic understanding still exists. Based on previous studies, in this paper, we further summarize the evolution and development of karst landforms into six stages: diagenetic, continental, mountain-forming, cluster, forest-forming, and primitive stages. On this basis, we also systematically summarize and detail five aspects: The calculation of weathering and soil-forming rate of carbonate rocks, diagnosis of soil water, evaluation of soil and water loss, interpretation and evolution of rocky desertification, and scientific measurement of ecosystem services. Despite the different research methods of different scholars in different times, the results are very different. However, after comprehensive consideration of the existing research results and the advantages and disadvantages of their application methods, the following conclusions were made. (1) Although the chemical weathering of carbonate rocks is very fast (30-130 mm ka(-1)), their soil formation rate is extremely slow due to their low content of acid-insoluble substances (within 5%), generally between 5 and 50 t km(-2) a(-1). (2) The soil is small and the distribution discontinuous, but the soil water content is relatively high, ranging from 0.2 to 0.4 m(3) m(-3). This may be related to the catchment effect of surrounding bedrock, and it will be dry in the future. (3) The modulus of soil erosion is low, generally between 2 and 200 t km(-2) a(-1). However, due to steep slope, heavy rainfall, and abrupt contact with rock and soil, the risk of soil erosion is very high, and there is a certain proportion of underground leakage. (4) The evolution of rocky desertification can be divided into three classic types, namely univariant, progressive, and retro-variant, but the method of rocky desertification resolution through decision tree and human-computer interaction is relatively efficient and accurate. (5) The evaluation model of karst ecosystem service function should be based on the soil formation rate to correct the water and soil conservation function and the climate adjustment function based on the karst geological carbon sink. At present, the indicators, methods, and models for diagnosing the health of the karst ecosystem must be improved and innovated to fully reflect the particularity of the karst region and the matching of the model methods, to improve the spatial and temporal resolution of the monitoring data (especially to establish a coupling model of the karst social-ecosystem), to accurately depict the response process of the karst ecosystem to climate change and human activities, and to improve the accuracy and predictability of the diagnostic model. In short, in this paper, we systematically summarize and detail the methods and major progress in diagnosing the health and sustainability of China's karst ecosystem and further propose the future research direction and breakthrough focus from the perspective of "rock soil water stone life", with a view to providing scientific and technological support for maintaining the ecological security and sustainable development of karst areas.