With the intensive research into global coupling relationships, ecological carrying capacity (ECC), seen as the crucial link between natural ecosystems and human systems, has gradually become an important tool for interdisciplinary research in ecology, resources science and environmental science, as well as for research on regional sustainable development. However, ECC research remains immature and lacks a complete theoretical system, as a result of many limiting factors and different space-time conditions. At present, Chinese and foreign studies focus on methods to evaluate ECC while neglecting to identify the internal driving mechanisms of ECC. In this article, based on the development and conceptualization of ECC, we introduce three evaluation methods for ECC: ecological footprint (EF), human appropriation of net primary production (HANPP) and ecosystem services consumption (ESC). Furthermore, we illuminate research focuses and developmental directions for ECC with respect to driving mechanisms, threshold, comprehensive evaluation systems and coupling dynamic model of multi ecological factors, in order to provide a reference for future ECC research.

As a concept to describe development restrictions, resources and environment carrying capacity (RECC) research has developed over more than 100 years since it was first proposed at the beginning of the 20^th century. It is now regarded as a significant factor in evaluating the level of cooperation between regional population, resources, and environment; and it is currently used as an effective and operational tool to guide regional sustainable development. This article first reviews the origin of RECC and its early headway. It then reviews the historical development of RECC from single factors, such as land resources carrying capacity, water resources carrying capacity and environmental carrying capacity (environmental capacity), to more comprehensive research, such as comprehensive evaluation, emergy analysis, and ecological footprint analysis. In general, it appears that comprehensive research will become increasingly important in RECC research. However, there are several deficiencies in the current state of comprehensive research. Firstly, comprehensive RECC research lacks a common measurement standard, though some scholars have attempted to create one. Secondly, the RECC evaluation of open systems and dynamic studies should be strengthened. Thirdly, more attention should be paid to standardization, digitalization, and systematization to promote the applicability of RECC research to national practical demands.

Research on the relationship between national resource constraint-region types and environmental carrying capacity is essential for the continued development of Chinese industrialization and urbanization. Thus, utilizing a series of key indexes including the per-capita potential of available land resources, the per-capita potential of available water resources, the degree of environmental stress, and the degree of ecological restriction, a step-by-step, integrated measuring method is presented here to understand the constrained carrying elements of water and land resources as well as environment and ecology. Spatial differences are analyzed and area types classified at the county level across China. Results reveal that: (1) Almost 90% of China is strongly constrained by both resources and the environment, while nearly 50% of national territory is strongly constrained by two elements, especially in areas of intensive population and industry to the east of the Helan-Longmen Mountain line; (2) Densely populated areas of eastern and central China, as well as on the Tibetan Plateau, are strongly constrained by a shortage of land resources, while North China, the northwest, northeast, the Sichuan basin, and some southern cities are experiencing strong constraints because of water shortages. In contrast, the North China plain, the Yangtze River delta, northern Jiangsu, Sichuan province, Chongqing municipality, Guizhou and Guangxi provinces, the northeast plain, and the northern Loess Plateau are constrained by high levels of environmental stress. Areas of China that are strongly ecologically constrained tend to be concentrated to the southwest of the Tianshan-Dabie Mountain line, as well as in the northeast on the Loess Plateau, in the Alashan of Inner Mongolia, in northeast China, and in the northern Jiangsu coastal area; (3) Constraints on national resources and environmental carrying capacity are diverse and cross-cut China, meanwhile, multi-element spatial distribution does reveal a degree of relative centralization. With the exception of the Tibetan Plateau which is resources-ecological constraint , other areas subject to cross constraints are mainly concentrated to the east of the Helan-Longmen Mountain line.