The definition, methods and key issues of grassland ecosystem carrying capacity

Grassland is the largest terrestrial ecosystem in China, and its important function is the material basis for the survival and development of herders. Simultaneously, the grassland ecosystem is fragile and sensitive, with serious degradation problems, posing a threat to ecological security and economic development. The study of the carrying capacity of grassland ecosystems is of great value to achieve the balance of grass-livestock, the sustainable use of grassland, and maintenance of ecological security in ecologically fragile areas in China. This paper combs through concepts related to the carrying capacity of grassland ecosystems, and proposes a conceptual framework for assessing the carrying capacity of grassland ecosystems. Based on the summary of the existing assessment methods of grassland ecosystem carrying capacity, this paper focuses on the research methods and quantitative models involved in the current carrying capacity of grassland ecosystems and finally analyzes the fields and directions that need to be strengthened in the future for the carrying capacity of grassland ecosystems. At present, methods for assessing grassland ecosystem carrying capacity mainly involve quantification using the livestock carrying capacity. Most of the existing methods incorporate estimations based on forage productivity, agricultural and sideline product prices, pasture yield, and net primary productivity, or normalized difference vegetation index. The existing problems are mainly: 1) grass yield is affected by multiple factors, in different study areas it varies greatly, and data is difficult to obtain or estimate accurately; 2) the amount of forage loss caused by wildlife, pests, and diseases is ignored; 3) stocking rate is converted without considering the weight and age of the livestock; and 4) there exists a lack of a multifactorial integration model and predictive and early warning model. Future research should be lucubrated as follows: 1) build a perfect basic theoretical system for grassland ecosystem carrying capacity research; 2) improve the evaluation index system of grassland ecosystem carrying capacity and optimize the evaluation model; 3) strengthen dynamic monitoring and standardization of parameters; and 4) establish prediction and early warning mechanisms, and scientifically determine the carrying threshold of grassland ecosystems.