Synthesis

INTRODUCTION

Changes in the state of ecosystems and social-ecological systems (SES) are not always linear, slow, or reversible. In many cases, changes are nonlinear, rapid, and irreversible (Scheffer et al. 2001, Biggs et al. 2018). The occurrence of the latter tends to have more severe negative impacts on human well-being and biodiversity (Scheffer et al. 2001). In the 1970s, important papers by Holling (1973) and May (1977) proposed concepts such as alternative stable states and ecological thresholds to understand these phenomena. They believed that there may be multiple stable states in the system under the same external conditions, and the system will shift from one stable state to another if external conditions cross the thresholds. Within 20 years after the publication of these two papers, ecologists began to try to confirm these new hypotheses in ecosystems. Scheffer’s study (1990) in shallow lake ecosystems found that there are two stable states: clear water and turbid water, and the change in total phosphorus (TP) concentration can control the shifts between these two stable states (Meijer 2000). These hypotheses were subsequently confirmed in more studies (Scheffer et al. 2001, Beisner et al. 2003, Ma et al. 2021). These concepts are believed to play an important role not only in scientific research revealing environmental changes, but also in environmental management, such as early warning of adverse changes and finding ways to prevent these changes (Groffman et al. 2006, Kelly et al. 2015, Sasaki et al. 2015). These have prompted interest in alternative stable states and ecological thresholds and have led scholars to widely discuss and explore them in more research fields.

The biggest gap between conceptual understanding and practical management is the lack of case studies (Biggs et al. 2018). Theories cannot be developed and successfully applied in management without being validated through extensive, long-term case studies (Walker et al. 2006). Because of the absence of unified, practical criteria for identifying and analyzing alternative stable states and ecological thresholds, conducting a comparative analysis and synthesis based on a limited number of research cases scattered around the world is quite challenging (Biggs et al. 2018). Resilience Alliance and Stockholm Resilience Centre scholars are aware of these serious problems. They have established databases, such as the Threshold Database (TDB, https://www.resalliance.org/thresholds-db) and Regime Shifts Database (RSDB, http://www.regimeshifts.org), to extensively collect existing relevant cases and potentially available data. They have also proposed consistent analysis frameworks for the research of regime shifts and ecological thresholds to guide scholars from different disciplines on how to carry out effective case studies and promote related theories’ development. However, most of the potentially usable case studies conducted in many countries and regions are published in native journals in their respective languages, making it challenging for data and experience from around the world to be widely exchanged.

In fact, dramatic environmental transitions are taking place globally (O'Brien and Barnett 2013). To continuously promote the development of relevant theories and to improve the ability to cope with the risks of environmental changes, experience and data accumulated in all countries and regions should be shared. Currently, governments of various countries attach great importance to international cooperation to jointly respond to the crisis of global environmental change (Smith et al. 2021). At the same time, there is also a need to strengthen the mutual exchange of experience in basic scientific research between countries. In response to environmental disasters and ecological degradation facing the country, Chinese scholars have conducted long-term monitoring and scientific research. However, almost none of these studies are included in TDB and RSDB. These data and experiences are also essential for promoting the development of relevant theories worldwide and dealing with global environmental changes.

China is one of the countries with the largest distribution of ecologically fragile areas (Gao et al. 2012). Affected by rapid development and construction, as well as climate warming and drying (Zhang et al. 2010) in the past few decades of the 20th century, a series of severe ecological degradation events occurred in these areas. For example, excessive deforestation caused terrible floods in the Yangtzi River (Yu et al. 2009), water pollution induced eutrophication and algal blooms in lakes of the Yangtzi River plain (Wang 2007), overgrazing led to sandstorms in North China (Dong et al. 2012), overexploitation of water resources resulted in groundwater-level declines and land subsidence in North China Plain (Liu et al. 2001), and reservoirs construction caused downstream lakes to dry up in Haihe basin (Feng 2006). In the past, Chinese scholars have carried out considerable amounts of qualitative and quantitative studies aimed at formulating ecosystem protection strategies and environmental management standards. These studies mainly focused on the identification of ecosystem change process and the quantitative detection of critical pressure-response nonlinear changes in the system (Fang et al. 2002, Wang et al. 2014, Su et al. 2019). They covered almost all types of ecosystems, and scientists have accumulated lots of basic monitoring data and research experience for various environmental changes, especially the unique environmental transitions occurring in China. However, these cases are scattered in different disciplines such as physical geography, agriculture, and forestry, and lack the guidance of a unified theoretical ecological paradigm. Few case studies have directly applied related concepts such as alternative stable states and ecological thresholds.

To this end, we developed the China Ecological Thresholds and Alternative Stable States Database (CETASSD, https://cetd.craes.cn/). On the one hand, the CETASSD continuously collects published data and cases to review and re-analyze past research, on the other hand, it builds a unified analysis framework to develop new case studies on ecological thresholds and alternative stable states. To date, the CETASSD has included more than 110 relevant research cases covering various ecosystems. The database aims to convert research cases scattered in various disciplines into more intuitive information that can be compared with each other. We encourage more targeted environmental monitoring and simulation experiments based on these potentially available information to detect more effective quantitative ecological thresholds. In addition, the database contains English keywords and abstracts of the original literature to allow for access by English readers, which provides a window for international scholars to understand and learn from the Chinese research experience.

DATABASE STRUCTURE AND UNIFIED ANALYSIS FRAMEWORK

Users of the CETASSD website can retrieve the desired cases using key items such as the ecosystem type, author, institution, keywords, location, biological group, and threshold type. Users can register for an account and add case studies published by themselves or others. When adding case information, they must follow the standardized description framework established by the database, extract and organize key information from the case, and enter it into each necessary description item. After submission, it is reviewed and approved by the administrator.

Analysis framework

The CETASSD has developed a standardized framework to describe the various alternative stable states and ecological thresholds that exist in ecosystems, with the aim of providing a convenient way for researchers and managers to obtain useful information from the database. The CETASSD refers to the TDB (Walker and Meyers 2004) and RSDB (Biggs et al. 2018) in the setting of a series of description items (Table 1). These items form a standard framework to disassemble and organize each valid case and redescribe the useful information in it. Three of the items (title, abstract, keyword) are provided in English to facilitate retrieval and reading by international users. There are differences in content between the case studies conducted by scholars in China and other countries; for example, China’s case studies rarely identify and explain the affected ecosystem services. Therefore, the CETASSD has some differences from the TDB and RSDB in terms of descriptive items. There is no descriptive item of ecosystem services in the CETASSD.

Case selection: two basic types of nonlinear changes

The CETASSD collects two basic types of nonlinear changes. The first are shifts of alternative stable states, that is, if the system has alternative attractors under the same external conditions. The definition of alternative stable states that we use is basically the same as that used in RSDB, that is, the transition of alternative stable states is considered to be large, persistent, and usually unexpected changes in SES that can have major impacts on ecosystem services (Biggs et al. 2018). Although in RSDB they are called regime shifts, in the CERASSD they are called alternative stable states. These changes often occur on large spatial scales, and their essence is often the reorganization of the system feedback network, which is manifested as a drastic change in the overall state of the system, such as the transformation of landscape types or the transformation of large-scale biological communities. In the CETASSD we classify the first category of changes as alternative stable states because we want to search for more evidence that alternative attractors exist in SES.

The second is abrupt changes in ecosystem quality, property, or phenomena. These changes are substantial changes that occur in a short period of time or within a smaller range of drivers relative to typical rates of change (Ratajczak et al. 2018, Turner et al. 2020). We collect the second nonlinear change, not to propose a completely independent type of change from the first, but to complement the relevant case studies of the former change. A discussion of alternative attractors is not necessary when analyzing these abrupt changes, and they emphasize quantitatively explaining how such nonlinear changes occur.

The CETASSD uses a relatively broad concept of ecological thresholds. The separatrix between two or more stable attractors is an important ecological threshold concept (Walker and Meyers 2004). However, most of the current research can only detect the time of the past and retroactive regime shift, and it is often very difficult to find a critical value for key drivers (Groffman et al. 2006. Hillebrand et al. 2020). In addition, we take the critical conditions for some huge abrupt changes that occur in SES as an important part of the ecological threshold. The numerical magnitude of the threshold is the magnitude of the key driver variable at the beginning of these abrupt changes. We use the term alternative stable states to refer to the phenomenon of the existence of alternative attractors in the ecosystem and to refer to shifts to alternative attractors.

Based on the above descriptions of the two basic types of change, we clarify the ecological threshold and alternative stable states concepts employed in this paper. The numerical magnitude of the threshold is the magnitude of the key driver variable at the beginning of these abrupt changes. We use the term alternative stable states to refer to the phenomenon of the existence of alternative attractors in the ecosystem.

RESULTS: BASIS AND CHARACTERISTICS OF CHINA’S RESEARCH

Alternative stable states

Although few case studies in China have directly used the concept of alternative stable states, the methods used and the issues solved are very similar to actual studies of alternative stable states. Therefore, these cases were considered as potentially valid cases and included in the database. The CETASSD currently includes 26 generic types of alternative stable states (Table 2), all of which have entered the research stage of identifying multiple stable states. Columns 2–5 of Table 2 summarize the common features that specific transitions of alternative stable states manifest in different case studies. Columns 6 and 7 list the representative and influential Chinese publications and their corresponding research locations for each type of alternative stable states research.

Research sites. There are many case studies carried out in inland arid regions and high altitude areas. From the geographical distribution of the 26 typical cases (Fig. 1), more than half of the cases are located in the northwestern region where the average annual precipitation is less than 400 mm or at high altitudes. Case studies in these regions can provide much evidence for studies on the impacts of climate change. The typical cases corresponding to the 26 types of alternative stable states in Table 2 cover the southeast coast, the rivers and lakes of the eastern plains, the western plateau and mountains, and the northwest arid and semiarid zones (Fig. 1). The typical cases of alternative stable states research included in the CETASSD cover a very wide space in China.

Systems: The alternative stable states documented to date have been most commonly found in terrestrial systems (nine alternative stable states), followed by the land-water interface (six alternative stable states). Very few case studies have been carried out in marine ecosystems (seagrass bed, coral reef, estuarine, mangrove).

Drivers: There are 14 different drivers of the alternative stable states currently collected in the CETASSD. These drivers can be mainly divided into two types: human activities and climate change. Among them, shifts between alternative stable states driven by human activities account for the majority (17 alternative stable states). The drivers caused by human activities include pollution emissions, fishing, overutilization of water resources, ecological water replenishment, dam construction, reclamation aquaculture, grazing, artificial introduction of species, and urban planning. The second category comprises the shifts between alternative stable states driven by climate change (9). Seven case studies are located in plateaus, mountains, and tundra, and two are in marine and coastal zones. Because of the sparse population in these areas, the ecosystem is less directly affected by human activities, and they are very sensitive to climate change, such as fluctuations in temperature and precipitation. In addition, coral reefs are susceptible to bleaching because of extremely low temperatures, and salt marsh vegetation is degraded because of the impact of rising sea levels.

Types: Alternative stable states numbered 1 to 2, 7 to 13, 16 to 18, and 21 to 22 can be regarded as documented alternative stable states, as the threshold and hysteresis effects of these types have been confirmed in the corresponding literature. On the other hand, types numbered 3 to 6, 14 to 15, 19 to 20, and 23 to 26 can only be considered potential alternative stable states because some key phenomena (such as threshold and hysteresis effects) have not been observed extensively and confirmed within these types. Compared with TDB and RSDB, the CETASSD mainly supplements four new types of alternative stable states. These new types are all located in the arid areas and high altitude areas of Northwest China. The four alternative stable states are briefly summarized below according to the analysis framework of the CETASSD.

Static sand to sand dunes

In the arid regions of Northwest China, activities such as grazing, agricultural planting, and urbanization have resulted in the destruction of surface vegetation, and the destruction of vegetation has exposed soil and resulted in desertification. When the intensity of human grazing exceeds the threshold, soil degradation makes it impossible for sandy vegetation to recover naturally, and the fixed sandy soil will be transformed into a permanently flowing sand dunes (Dong et al. 1996). At the same wind speed, flowing sand is more likely to raise dust (He et al. 2013). A large amount of dust flows into the upper atmosphere in the western region, and the strong westerly winds in winter transfer the dust to the North China Plain and the Pacific Ocean thousands of kilometers away from the region. Sandstorms seriously affect the air quality in the densely populated areas in the east, and the impact of dustfall on marine ecosystems is also significant (Hu et al. 2021). This shows cross-scale and cross-regional effects of environmental shifts.

Xerobiochemical of permafrost vegetation

Global warming is causing the temperature of the permafrost surface to rise, which causes the permafrost to gradually thaw (Wang et al. 1996). After the top layer of permafrost in the soil thaws significantly, the burial depth of the permafrost in the soil increases significantly. Because of the lack of the blocking effect of the permafrost on the infiltration of the upper soil moisture, the surface soil moisture content gradually decreases. When the burial depth of the frozen soil increases to a certain level, the moisture content of the upper soil decreases to a threshold that cannot support the growth of the original vegetation. The original abundant and diverse wet vegetation begins to be gradually replaced by a small amount of single species of xerophytic vegetation, and the ecosystem that depended on the vegetation coverage type changes significantly (Liang et al. 2007). This shows how global climate change affects fragile ecosystems in alpine areas.

Northwest China water cycle change

Around 1987, the impact of global warming on precipitation and runoff patterns in northwestern China, mainly in Xinjiang, reached a tipping point, causing sudden climate changes in these regions. These changes are manifested in a significant increase in precipitation, glacial melt and runoff, a significant rise in the water level of inland lakes, and a rapid increase in flood disasters. This indicates that the climate pattern in Northwest China has shifted from warm-dry to warm-wet (Shi et al. 2003). Climate warming and wetting and the associated changes in water cycle patterns will have a continuous impact on the ecosystems in the arid regions of Northwest China (Shi 2003).

Climate warming and wetting in Three-River Headwater Region

Climate warming has also brought about climate warming and wetting with rising temperature and increased precipitation in Three-River Headwater Region. However, unlike the geographical conditions in Xinjiang, the Three-River Headwater Region is located on the eastern edge of the Qinghai-Tibet Plateau, which is widely distributed with seasonal frozen soil and permafrost. When the effect of increased precipitation and increased temperature exceeds a critical point, the increase of permafrost depth caused by rising temperature is faster than the increase in precipitation. At this time, water systems such as lakes and rivers begin to shrink significantly, and high-coverage alpine meadows and swamp meadows degenerate into low-coverage grasslands (Hu 2009). The runoff reduction caused by the climate pattern transition in Three-River Headwater Region has a significant impact on the middle and upper reaches of the Yangtze and Yellow Rivers (Zhang et al. 2011). This shows the complexity of the impact of climate change in the plateau and alpine areas.

Ecological thresholds

Here, we introduce ecological thresholds included in the CETASSD. In the CETASSD, cases that conform to the concept of ecological thresholds proposed earlier were selected and included from quantitative studies carried out by Chinese researchers. These cases are from 14 types of ecosystems such as rivers, lakes, and forests. Table 3 lists 60 typical representative cases. These cases describe and simulate key environmental changes from the perspective of different pressure-response relationships. Table 3 shows the results of the quantitative test in each typical case and briefly describes the specific connotation of the ecological threshold. The second and fourth columns are the pressure factors and their quantitative values in the corresponding ecological threshold research.

Types: Out of all the cases currently included in the CETASSD, only five cases have detected the transition threshold for alternative stable states. Two of the cases detected the threshold of bidirectional conversion for alternative stable states (Wang 2007, Hu et al. 2010), and three cases only detected the threshold of a single conversion direction (Dong et al. 1996, Liu et al. 2014, Zheng et al. 2005). Almost all the threshold analyses performed in other cases only studied local nonlinear changes in the SES, and the detection of transition threshold for alternative stable states has not been performed.

Ecosystems: Sixty typical cases of ecological thresholds currently included in the CETASSD cover almost all ecosystem types in China. These cases have been most commonly found in forests (11 cases), followed by lake, farmland, desert, and urban (six cases). There were five cases in tundra ecosystems. However, the number of typical cases in the four marine ecosystems (seagrass bed, coral reef, estuarine, mangrove) was the lowest (one case or two cases). The CETASSD currently contains only nine cases on ecological thresholds from marine systems.

Stresses: In terms of the key stresses studied in typical cases, 51 of the 60 cases analyzed the effect of abiotic environmental factors (e.g., temperature, precipitation, slope, salinity, pollutant concentration, and groundwater depth). The most commonly studied environmental stress is temperature (eight cases), followed by water level (six cases, including groundwater depth) and salinity (six cases). In addition to environmental stress, nine cases analyzed the effect of biological indicators (such as fish density, stocking capacity, and vegetation coverage).

Access to data: There is great emphasis on ecological threshold studies by observing nonlinear changes over spatial gradients. The data acquisition methods in ecological threshold research are mainly divided into two types: dynamic monitoring of time series and observation along spatial gradients. Dynamic monitoring on time series is the most commonly used method for data acquisition. However, according to the research methods of each case summarized in the CETASSD, the cases carried out by Chinese scholars based on the data collected by spatial observation also accounted for a very large proportion. Among the 60 typical cases in Table 3, 24 cases adopted the method of spatial observation to obtain the required data.

Analytical methods: In almost all cases, complex changes are simplified by identifying the most critical drivers and responses, and constructing a “stressor-response” process line. Under the premise of fully understanding the direct or indirect interaction in SES, we identify the most critical drivers that cause nonlinear changes and use them as the horizontal axis (i.e., pressure variables) of the process line, and then identify the responses that can best represent the state change of SES and are most sensitive to the change of the drivers as the vertical axis (i.e., response variables). Stressors are generally environmental conditions or system parameters with practical ecological significance, and responses can be parameters with practical significance or statistical indicators that indirectly reflect system structure, state, and function.

DISCUSSION

Characteristics and enlightenment of Chinese case studies

The summary of the Chinese case studies highlights three main features. First, more types of alternative stable states were identified in the western arid area and Qinghai-Tibet Plateau. Second, Chinese researchers attach great importance to the study of critical threshold of environmental gradients. Third, ecological threshold analysis is mainly carried out by constructing a highly generalized “stress-response” process line. We discuss new discoveries and insights that these characteristics may provide for theoretical development and sustainable environmental management of the world.

More than half of the alternative stable states currently included are distributed in the arid and high altitude areas of western China. North China has been affected by sandstorms in the west for a long time (Liu et al. 2002). The upper reaches of major rivers such as the Yangtze River and the Yellow River are all located on the Qinghai-Tibet Plateau. In recent decades, the upstream water volume has fluctuated, which affects the downstream water resources and river ecosystems (Hou et al. 2012). These backgrounds may be what drives Chinese scholars to conduct a lot of research in the western and plateau regions. These studies find that localized destruction of vegetation by human activities may contribute to dust storms sweeping from inland to ocean (Dong et al. 1996, Hu et al. 2021). Continued global warming will significantly alter climate patterns in inland arid areas that are supplied with meltwater from mountain snow as the only water source (Shi et al. 2003). Climate change causes large-scale vegetation degradation (Liang et al. 2007) and adversely affects downstream river ecosystems by reducing runoff (Hu 2009) in alpine permafrost. These studies have provided substantial evidence for understanding the impact of global climate change on ecosystems in continental non-monsoon climate zones, as well as plateau and alpine areas. At the same time, these studies fully demonstrate that many large-scale environmental changes are cross-regional and even global. This prompts us to strengthen international cooperation in response to environmental changes, and encourage more countries and regions to participate in related research.

The studies on the critical threshold of environmental gradients may have important implications for developing a methodology for studying nonlinear changes in SES. Whether in China or other countries, dynamic monitoring on time series is the main method used to obtain data (Meijer 2000, Yi et al. 2020). However, for some environmental changes that have already occurred, it is difficult for people to accurately obtain past parameters that describe the process of these changes. Observation on spatial gradient is therefore a potentially useful method for studying nonlinear changes and an alternative method for threshold detection. China has a very wide area and a very diverse type of ecotones (i.e., transition areas at the interface between two different types of ecosystems; Gao et al. 2012). In these ecotones, there are very obvious spatial gradients in human impacts, environmental conditions, and climate patterns. The case studies accumulated in the long-term research on critical thresholds of environmental gradients by Chinese scholars can substantially contribute to promoting the research methods of ecological thresholds.

The analysis approach of threshold positions detection through trend analysis of the “stress-response” process line provides intuitive, visual, and highly generalized conclusions for researchers and managers. This approach improves people’s ability to understand complex changes (Lade et al. 2021). This approach has great advantages and value in ecological threshold research, and many international scholars have developed similar analysis methods (Toms and Lesperance 2003, Andersen et al. 2009). However, accurate identification of the stress and response variables that build the process line can only be achieved with a sufficient understanding of the feedback mechanism at specific scales.

The environmental changes that have occurred in China in recent decades are very diverse and complex, and in the past, research was very fragmented and there was a lack of systematic understanding of the changes. With the introduction of related theories such as alternative stable states and ecological threshold, researchers have developed a paradigm that can understand complex changes from a systematic and multi-scale perspective. This will not only improve the ability of Chinese managers to deal with the risks of environmental transitions and improve the ability of sustainable environmental management, but also provide more new discoveries and reference experience for promoting relevant research in the world.

Contributions of the developing the CETASSD

The CETASSD provides a platform for researchers interested in nonlinear changes in ecosystems to learn and communicate. We encourage researchers to use the unified analytical framework established by the database to conduct new case studies, which will help to form comparable conclusions. Researchers can also reorganize their own or others’ relevant research results according to the analysis framework of the database, and publish new cases on the website, which is also the main force for the sustainable development of the database. In addition, CETASSD provides managers with a convenient way to screen scientific references. Some quantitative ecological thresholds collected in the database can be used to formulate a standard system for environmental management. The information restructured in CETASSD facilitate managers’ more accurate understanding of complexity of ecosystem changes, which helps them come up with more scientific and effective strategies for environmental governance.

China’s unique geographical conditions are the foundation that cannot be ignored in the study of world environmental change. China has some unique geographical and climatic conditions and cultural backgrounds, which have led to a series of unique ecosystem changes in China. For example, the Qinghai-Tibet Plateau in western China is the highest plateau in the world, and its unique geographical features shape unique climatic and ecological processes (Qin 1977). In the vast agro-pastoral zone in northwestern China (Cheng 2002) and the hilly areas in southwestern China (Geng and Zhang 2021), there is an agricultural civilization and historical background unlike any other region in the world, forming a unique social-ecological complex system in these places. The CETASSD summarizes these unique changes using a unified conceptual framework to provide more evidence and basis for internationally relevant theoretical developments.

With the emergence of the effectiveness of China’s ecological restoration projects (Chen et al. 2019a), an increasing number of cases of reversal of ecosystem degradation will be included in the CETASSD. In the past 10 years, the Chinese government has promoted construction of ecological civilization and delimited the Ecological Conservation Red Line (ECRL). More than one-quarter of the Chinese mainland is included in the red line to be protected (Gao 2019), and almost all key ecological function zones and ecologically fragile zones in China will be included in the ECRLs (He et al. 2018). Strict environmental management has promoted the restorative transitions of damaged ecosystems, and benign shifts of alternative stable states and events of thresholds crossed are increasing. For example, through ecological water replenishment in 2020, the dry downstream Yongding River re-opens its entire mainstream with water, and the river ecosystem was gradually restored (Sun et al. 2021). A global study found that between 2000 and 2017, the newly increased area of vegetation in China accounted for at least 25% of the newly increased area of vegetation in the world (Chen et al. 2019a). This is mainly due to long-term afforestation projects in the desertified areas of the forest-steppe ecotone in North China. Large areas of wasteland and sandy land are gradually being replaced by closed forests. These studies provide valuable scientific references for ecosystem protection and restoration in other similar regions around the world. The CETASSD, which continues to pay attention to and include these cases, will play a greater role in promoting theoretical development and supporting environmental management.

Although there are some thresholds that have important applications in management, we need to recognize that most thresholds are far from being successfully applied in management. There are only a few detected quantitative ecological thresholds or critical points that have been successfully applied in environmental management, and they can improve human ability to deal with some major environmental disasters (e.g., agricultural development is likely to cause large-scale soil erosion when the slope is greater than 25°, and the slope of 25° has been incorporated into the legal documents of China’s soil and water conservation as a management standard; NPC 2010). However, for most ecological thresholds, they are characterized by uncertainty (Groffman et al. 2006, Hillebrand et al. 2021), and their values ​​correspond to some specific time and place (Johnson 2013, Hillebrand et al. 2021). Thresholds for the same class can vary widely across time and place. This means that even based on long-term monitoring data, what appears to be a very reliable threshold in one area may still be difficult to apply in another area. Not only that, but the existing mathematical methods are also difficult to achieve very accurate results when determining the position of the threshold (Daily et al. 2012, Lade et al. 2021). Therefore, managers should be very cautious in viewing and using thresholds.

Research agenda

According to the summary of the cases included in the CETASSD, we present an outlook for case studies on ecological thresholds and alternative stable states. First, re-examine past research cases and methods with the latest theories, and promote the development of quantitative research and methods in a targeted manner. Second, strengthen research in certain ecosystems such as the ocean in China. Third, strive to bridge the gap between ecological thresholds and implementing management applications.

To promote quantitative research and method development of alternative stable states, it is necessary to revisit past research to ensure that it is up-to-date with the latest theories. Scholars have conducted long-term observation and investigation in the past, providing preliminary understanding of the dynamic processes of many changes, including the nonlinearity, persistence, and irreversibility of changes. Some of this information can be considered effective knowledge of alternative stable states and ecological thresholds, whereas most can only be regarded as hypotheses. Many studies in this field remain at the qualitative and semi-quantitative stages. To address this gap, it is necessary to carry out targeted environmental monitoring and simulation experiments to verify these preliminary understandings and hypotheses. When promoting quantitative research, it is important to correctly understand and explore the uncertainty of thresholds and avoid overestimating them. Furthermore, the experimental settings, survey methods, and data analysis methods used in past studies need to be revisited. Continual development of more effective methods is required to meet current and future environmental management needs.

Research needs to be strengthened in certain ecosystems, such as the ocean. According to the results of this paper, it can be seen that in China, the current research level and progress on various types of alternative stable states are uneven. Although research on the ecosystem transition in lake and arid areas is relatively in-depth, for some other types of ecosystems in China, such as seagrass beds, coral reefs, estuaries, and mangroves, the mechanisms of alternative stable states has not yet been established, and some important ecological thresholds have not been extensively detected. Despite mechanisms for many of the same types of alternative stable states having been proposed in other regions, because of the significant differences between regions, China needs to conduct local research. As a result, from the 1970s to the early 2000s, factors such as coastal urbanization, sewage discharge, fishery reclamation, and extreme climates led to the disappearance and degradation of mangroves, coral reefs, and seagrass beds in China (Qiu 2012, Peng et al. 2008, Zheng et al. 2013). Hence, increased funding for basic research is urgently needed, along with strengthened research on alternative stable states and ecological thresholds, to support marine ecosystems protection, restoration, and management in China.

To enhance environmental management, we need to facilitate the application of thresholds. Effective ecological thresholds have significant application value in environmental management (Groffman et al. 2006). Research on alternative stable states and ecological thresholds should focus on addressing important ecological and environmental issues. While conducting in-depth basic mechanism research, we should vigorously develop the application value of research results in management. We must ensure scientific rigor, accuracy, and effectiveness in the quantitative detection of ecological thresholds, and form the threshold results into quantitative and practical standards in environmental management as soon as possible. The successful application of thresholds in environmental protection can enable effective ecological restoration, monitoring, and early warning of major environmental changes.

CONCLUSION

The CETASSD provides a unified framework to reorganize and summarize useful information, which was scattered among case studies in various research fields, to promote worldwide research on alternative stable states and ecological thresholds and has significant value for environmental management. A summary analysis of all the cases in the database indicates that China’s case studies have a solid foundation and serve as a significant driving force in promoting worldwide research on alternative stable states and ecological thresholds. A large number of new studies conducted by Chinese scholars on alternative stable states in arid areas and high-altitude areas have provided valuable evidence and explanation to reveal the impact of global climate change. Critical thresholds of environmental gradients studied by Chinese researchers may become important topics for future research on alternative stable states and ecological thresholds. The CETASSD, like the TDB and RSDB, has added many new and effective empirical cases. Considering the continuous increases in the Chinese government’s investment in basic ecological research, the CETASSD will become a vital database and will continue to track and collect relevant research cases.

In order to improve the resilience of SES to environmental risks and enhance sustainable management capabilities, we provide an outlook. First, we suggest the re-examination of past research cases and methods with the latest theories, and promotion of targeted quantitative research and methods. Second, we recommend an increase in research in specific ecosystems, such as the ocean. Third, we encourage the application of thresholds in management. Simultaneously, we hope that the framework provided by the CETASSD can guide future research in China on alternative stable states and ecological thresholds, which should be carried out in-depth using standard and normalized methods. We also hope that the quantitative data collected in the database can serve as a strong basis to support governments, enterprises, and other stakeholders in formulating management standards.

LITERATURE CITED

An, Y. T., and D. Hou. 2015. Research on the relationship between urban permeable area and rainfall runoff reduction. Scientific and Technological Innovation (21): 82-83. [Translated from the Chinese.] http://dx.doi.org/10.3969/j.issn.1673-1328.2015.21.078

Andersen, T., J. Carstensen, E. Hernández-García, and C. M. Duarte. 2009. Ecological thresholds and regime shifts: approaches to identification. Trends in Ecology & Evolution 24(1):49-57. https://doi.org/10.1016/j.tree.2008.07.014

Beisner, B. E., D. T. Haydon, and K. Cuddington. 2003. Alternative stable states in ecology. Frontiers in Ecology and the Environment 1(7):376-382. https://doi.org/10.1890/1540-9295(2003)001[0376:ASSIE]2.0.CO;2

Biggs, R., G. D. Peterson, and J. C. Rocha. 2018. The Regime Shifts Database: a framework for analyzing regime shifts in social-ecological systems. Ecology and Society 23(3):9. https://doi.org/10.5751/ES-10264-230309

Bureau of Hydrology of Ministry of Water and Power of PRC (BHMWP). 1987. Evaluation of China’s water resources. China Water & Power Press, Beijing, China. [Translated from the Chinese.]

Chen, C., T. Park, X. Wang, S. Piao, B. Xu, R. K. Chaturvedi, R. Fuchs, V. Brovkin, P. Ciais, R. Fensholt , H. Tømmervik, G. Bala, Z. Zhu, R. R. Nemani, and R. B. Myneni. 2019a. China and India lead in greening of the world through land-use management. Nature Sustainability 2:122-129. https://doi.org/10.1038/s41893-019-0220-7

Chen, H. L., Y. W. Ou, F. L. Lyu, Y. D. Song, and R. Hao. 2019b. Variation of vegetation cover and its correlation of topographic factors in Guandu River basin. Research of Soil and Water Conservation 26(3): 135-140. [Translated from the Chinese.] http://dx.doi.org/10.13869/j.cnki.rswc.2019.03.019

Chen, J., G. F. Liang, and S. Y. Ding. 2012. Landscape connectivity analysis for the forest landscape restoration: a case study of Gongyi City. Acta Ecologica Sinica 32(12):3773-3781. [Translated from the Chinese.] http://dx.doi.org/10.5846/stxb201108171210

Chen, S. S., S. Y. Zang, and L. Sun. 2018. Permafrost degradation in Northeast China and its environmental effects: present situation and prospect. Journal of Glaciology and Geocryology 40(2):298-306. [Translated from the Chinese.]

Cheng, X. 2002. Unique ecosystem characters and ecological principles for development in the ecotones between agriculture and pasture in north China. Chinese Journal of Applied Ecology 13(11):1503-1506. [Translated from the Chinese.]

Cui, B. S., Q. He, and X. S. Zhao. 2008. Researches on the ecological thresholds of Suaeda salsa to the environmental gradients of water table depth and soil salinity. Acta Ecologica Sinica 28(4):1408-1418. [Translated from the Chinese.] http://dx.doi.org/10.3321/j.issn:1000-0933.2008.04.008

Cui, L. J., D. M. Bao, H. Xiao, M. Y. Zhang, and C. G. He. 2006. Analysis on the eco-environmental water requirement and the water supply strategy of Zhalong wetland. Journal of Northeast Normal University (Natural Science Edition) 38(3):128-132. [Translated from the Chinese.] http://dx.doi.org/10.3321/j.issn:1000-1832.2006.03.028

Daily, J. P., N. P. Hitt, D. R. Smith, and C. D. Snyder. 2012. Experimental and environmental factors affect spurious detection of ecological thresholds. Ecology 93(1):17-23. https://doi.org/10.1890/11-0516.1

Dong, J. L., S. Y. Zou, and L. J. Zou. 2012. Distribution characteristics and influencing factors of sandstorms in Inner Mongolia. Journal of Arid Land Resources and Environment 26(5):67-72.

Dong, Z. B., W. N. Chen, G. R. Dong, G. T. Chen, Z. S. Li, and Z. T. Yang. 1996. Influences of vegetation cover on the wind erosion of sandy soil. Acta Scientiae Circumstantiae 16(4):437-443. [Translated from the Chinese.]

Fan, H. L. 2017. Response of submerged plant to different nutritional conditions and water depth gradient. Thesis. Anhui University of Science and Technology, Huainan, Anhui, China. [Translated from the Chinese.] http://dx.doi.org/10.7666/d.Y3236810

Fang, J. Y. 1994. Arrangement of East-Asian vegetation types on coordinates of temperature and precipitation. Acta Ecologica Sinica 14(3):290-294. [Translated from the Chinese.]

Fang, J. Y., Y. C. Song, H. Y. Liu, and S. L. Piao. 2002. Vegetation-climate relationship and its application in the division of vegetation zone in China. Acta Botanica Sinica 44(9):1105-1122.

Feng, Q. 2006. Analysis of the shallow groundwater resource in hyperarld region. Pages 451-456 in Study of the strategy of land resources and regional harmonious development in China, Nanning, Guangxi, China. China Meteorological Press, Beijing, China. [Translated from the Chinese.]

Gao, J. 2019. How China will protect one-quarter of its land. Nature 569(7757):457. https://doi.org/10.1038/d41586-019-01563-2

Gao, J., S. H. Lyu, Z. R. Zheng, and J. H. Liu. 2012. Typical ecotones in China. Journal of Resources and Ecology 3(4):297-307. https://doi.org/10.5814/j.issn.1674-764x.2012.04.002

Gao, X. Q., J. C. Ren, Z. X. Zong, and X. M. Cai. 1994. Studies on the nutrient energetics of Microcystis aeruginosa. Acta Scientiarum Naturalium Universitatis Pekinensis 30(4):461-469. [Translated from the Chinese.] http://dx.doi.org/10.13209/j.0479-8023.1994.067

Geng, Y. P., and D. Zhang. 2021. Hani Terraces of Honghe: a coommunity of life for man and nature. Science (China) 73(05):11-15. [Translated from the Chinese.]

Groffman, P. M., J. S. Baron, T. Blett, A. J. Gold, I. Goodman, L. H. Gunderson, B. M. Levinson, M. A. Palmer, H. W. Paerl, G. D. Peterson, et al. 2006. Ecological thresholds: the key to successful environmental management or an important concept with no practical application? Ecosystems 9:1-13. https://doi.org/10.1007/s10021-003-0142-z

Guo, K., X. J. Dong, and Z. M. Liu. 2000. Characteristics of soil moisture content on sand dunes in Mu Us sandy grassland: why Artemisia ordosica declines on old fixed sand dunes. Chinese Journal of Plant Ecology 24(3):275-279. [Translated from the Chinese.]

Hao, X. M., W. H. Li, and Y. N. Chen, 2008. Water table and the desert riparian forest community in the lower reaches of Tarim River, China. Chinese Journal of Plant Ecology 32(4):838-847. [Translated from the Chinese.]

He, J., X. H. Wu, T. T. Yang, and P. Li. 2013. Research on sand-fixing function of grassland based on threshold wind velocity. Chinese Journal of Grassland 35(5): 103-107. [Translated from the Chinese.]

He, P., J. X. Gao, W. G. Zhang, S. Rao, C. X. Zou, J. Q. Du, and W. L. Liu. 2018. China integrating conservation areas into red lines for stricter and unified management. Land Use Policy 71:245-248. https://doi.org/10.1016/j.landusepol.2017.11.057

He, Z. L., R. L. Cao, W. R. Huo, Y. Zhou, and J. J. Wang. 1990. Study on the critical concentration of cadmium in paddy soil—on neutral or alkaline soil. Journal of Agro-Environment Science 9(4):10-12. [Translated from the Chinese.]

Hillebrand, H., I. Donohue, W. S. Harpole, D. Hodapp, M. Kucera, A. M. Lewandowska, J. Merder, J. M. Montoya, and J. A. Freund. 2020. Thresholds for ecological responses to global change do not emerge from empirical data. Nature Ecology & Evolution 4:1502-1509. https://doi.org/10.1038/s41559-020-1256-9

Hillebrand, H., I. Donohue, W. S. Harpole, D. Hodapp, M. Kucera, A. M. Lewandowska, J. Merder, J. M. Montoya, and J. A. Freund. 2021. Reply to: Empirical pressure-response relations can benefit assessment of safe operating spaces. Nature Ecology & Evolution 5:1080-1081. https://doi.org/10.1038/s41559-021-01484-2

Holling, C. S. 1973. Resilience and stability of ecological systems. Annual Review of Ecology Evolution and Systematics 4(4):1-23. https://doi.org/10.1146/annurev.es.04.110173.000245

Hou, S. Z., P. Wang, and W. B. Chu. 2012. Analysis of water and sediment changes in Upper Yellow River. Journal of Sediment Research (4):46-52. [Translated from the Chinese.] http://dx.doi.org/10.16239/j.cnki.0468-155x.2012.04.007

Hu, H. C. 2009. The research on the hydrological cycle based on the synergistic effect of vegetation and frozen soil in the source region of Yangtze and Yellow River. Thesis. Lanzhou University, Lanzhou, Gansu, China. [Translated from the Chinese.]

Hu, W. J., L. Ma, X. Q. Wu, and K. B. Zhang. 2021. Dust storms forward trajectories and influence range over the Mu Us Desert. Acta Scientiarum Naturalium Universitatis Pekinensis 57(6):1161-1171. [Translated from the Chinese.]

Hu, Z. P., G. Ge, C. L. Liu, F. S. Chen, and S. Li. 2010. Structure of Poyang lake wetland plants ecosystem and influence of lake water level for the structure. Resources and Environment in the Yangtze Basin 19(6):597-605. [Translated from the Chinese.]

Huai, B. J., Z. Q. Li, M. P. Sun, P. Zhou, and Y. Xiao. 2014. RS analysis of glaciers change in the Heihe River Basinin the last 50 years. Acta Geographica Sinica 69(3):365-377.

Huang, H. C. 2014. An study of the mechanism of the urban heat island formation, evolution and planning strategies. Thesis. Tianjin University, Tianjin, China. [Translated from the Chinese.]

Jiao, J. Y., W. Z. Wang, and J. Li. 2000. Effective cover rate of woodland and grassland for soil and water conservation. Chinese Journal of Plant Ecology 24(5):608-612. [Translated from the Chinese.]

Jin, X. S., and J. Y. Deng. 2000. Variations in community structure of fishery resources and biodiversity in the L aizhou Bay, Shandong. Biodiversity Science 8(1): 65-72. [Translated from the Chinese.] http://dx.doi.org/10.3321/j.issn:1005-0094.2000.01.009

Johnson, C. J. 2013. Identifying ecological thresholds for regulating human activity: effective conservation or wishful thinking? Biological Conservation 168(4):57-65. https://doi.org/10.1016/j.biocon.2013.09.012

Kelly, R. P., A. L. Erickson, L. A. Mease, W. Battista, J. N. Kittinger, and R. Fujita. 2015. Embracing thresholds for better environmental management. Philosophical Transactions of the Royal Society B Biological Sciences 370(1659):20130276. https://doi.org/10.1098/rstb.2013.0276

Lade, S. J., L. Wang-Erlandsson, A. Staal, and J. C. Rocha. 2021. Empirical pressure-response relations can benefit assessment of safe operating spaces. Nature Ecology & Evolution 5:1078-1079. https://doi.org/10.1038/s41559-021-01481-5

Li, J., Y. H. Wang, R. S. Zhang, Y. J. Ge, D. L. Qi, and D. F. Zhang. 2006. Disaster effects of sea level rise: a case of Jiangsu Coastal Lowland. Scientia Geographica Sinica 26(1):87-93. [Translated from the Chinese.]

Li, N., and C. Liu. 2012. Study on ecological thresholds of the landscape defragmentation. Chinese Horticulture Abstracts 28(5):69-71. [Translated from the Chinese.] http://dx.doi.org/10.3969/j.issn.1672-0873.2012.05.033

Li, W. 2018. Responses and thresholds of typical salt march species to flooding-salinity stress in Yangtze Estuary. Thesis. East China Normal University, Shanghai, China. [Translated from the Chinese.]

Li, W. C., and G. H. Lian. 1996. Light demand for brood-bud germination of submerged plant. Journal of Lake Sciences 8(S1):25-30. [Translated from the Chinese.] http://dx.doi.org/10.18307/1996.sup04

Li, W. H., H. H. Zhou, X. M. Yang, and H. Ding. 2010. Temporal and spatial distribution characteristics of aboveground biomass of grassland plant communities in an arid area. Acta Prataculturae Sinica 19(5):186-195. [Translated from the Chinese.]

Li, X. Y., L. S. Lin, and Q. Zhao. 2009. Distribution of dominant plant species and characteristic of its communities on the foreland of Cele Oasis in relation to groundwater level. Arid Land Geography 32(6):906-911. [Translated from the Chinese.] http://dx.doi.org/10.13826/j.cnki.cn65-1103/x.2009.06.019

Li, Y. N., S. Yuan, H. P. Fu, X. D. Wu, C. Yue, D. H. Man, S. W. Yang, L. N. Ye, and J. R. Wang. 2018. Relationship of rodent densities with forage loss in typical steppe. Acta Theriologica Sinica 38(4):369-376. [Translated from the Chinese.] http://dx.doi.org/10.16829/j.slxb.150131

Li, Z. P. 2012. Stress of main environmental factors on Poritidae. Thesis. Guangdong Ocean University, Zhanjiang, Guangdong, China. [Translated from the Chinese.]

Liang, S. H., L. Wan, Z. M. Li, and W. B. Cao. 2007. The effect of permafrost on alpine vegetation in the source regions of the Yellow River. Journal of Glaciology and Geocryology 29(1):45-52. [Translated from the Chinese.] http://dx.doi.org/10.3969/j.issn.1000-0240.2007.01.008

Liao, S. F., X. Wang, Z. C. Xie, S. Y. Liu, J. Lin, and Z. L. Jiang. 2015. Changes of glacial lakes in different watersheds of Chinese Himalaya during the last four decades. Journal of Natural Resources 30(2):293-303. [Translated from the Chinese.]

Liu, C. M., J. J. Yu, and E. Kendy. 2001. Groundwater exploitation and its impact on the environment in the North China Plain. Water International 26(2):265-272. https://doi.org/10.1080/02508060108686913

Liu, H. X. 1981. The vertical zonation of mountain vegetation in China. Acta Geographica Sinica 36(3):267-279. [Translated from the Chinese.] http://dx.doi.org/10.11821/xb198103003

Liu, J. K., and P. Xie. 1999. Unraveling the enigma of the disappearance of water bloom from the East Lake (Lake Donghu) of Wuhan. Resources and Environment in the Yangtze Basin 8(3):85-92. [Translated from the Chinese.]

Liu, L., Z. P. Li, Y. C. Shen, and X. D. Yang. 2013a. Study of stress of four environmental factors on Porites lutea and Goniopora stutchburyi. Journal of Tropical Oceanography 32(3):72-77. [Translated from the Chinese.] http://dx.doi.org/10.3969/j.issn.1009-5470.2013.03.011

Liu, P. P., J. H. Bai, Q. S. Zhao, J. J. Wang, and Q. Q. Lu. 2013b. A review on terrestrialization and primary productivity of aquatic vegetations in lake ecosystems. Wetland Science 11(3):392-397. [Translated from the Chinese.] http://dx.doi.org/10.3969/j.issn.1672-5948.2013.03.015

Liu, T., Y. M. Gan, H. X. Zhang, S. J. Yang, Z. Q. Song, P. B. Fu, and X. B. Zhang. 2014. A study on the appropriate stocking capacity under group-household management on the Hongyuan grasslands in north-western Sichuan. Acta Prataculturae Sinica 23(3):197-204. [Translated from the Chinese.]

Liu, X. C., Y. Zeng, X. F. Qiu, and Q. L. Miu. 2002. Sand-dust storms invading Beijing. Journal of Nanjing Institute of Meteorology 25(1):118-123. [Translated from the Chinese.] http://dx.doi.org/10.13878/j.cnki.dqkxxb.2002.01.017

Luo, H. H., Q. Li, and Z. Li. 2012. The impact of water temperature during the fish reproduction in the upper Yangtze River due to the cascade development in the lower Jinsha River. Journal of China Institute of Water Resources and Hydropower Research 10(4):256-259. [Translated from the Chinese.] http://dx.doi.org/10.13244/j.cnki.jiwhr.2012.04.010

Luo, T. X., W. H. Li, Y. F. Leng, and Y. Z. Yue. 1998. Estimation of total biomass and potential distribution of net primary productivity in the Tibetan plateau. Geographical Research 17(4):337-345. [Translated from the Chinese.] http://dx.doi.org/10.3321/j.issn:1000-0585.1998.04.001

Luo, Y. Q., G. W. Song, R. G. Liu, and J. G. Li. 1999. Preliminary study on ecological threshold of poplar longicorn beetle. Journal of Beijing Forestry University 21(6):49-55. [Translated from the Chinese.]

Ma, H., B. L. Zhong, H. Yue, and S. X. Cao. 2015. Research on the application of natural ecological restoration in a typical region of China with red soils. Acta Ecologica Sinica 35(18):246-254. [Translated from the Chinese.] http://dx.doi.org/10.5846/stxb201401210161

Ma, M. J., S. Collins, Z. Ratajczak, and G. Du. 2021. Soil seed banks, alternative stable state theory, and ecosystem resilience. BioScience 71(7):697-707. https://doi.org/10.1093/biosci/biab011

Ma, W. W., H. Wang, Y. S. Wang, R. Huang, and X. W. Shi. 2014. Changes of soil properties and water conservation function in the degradation process of Gahai Peat Bog in Gannan. Journal of Natural Resources 29(9):1531-1541. [Translated from the Chinese.] http://dx.doi.org/10.11849/zrzyxb.2014.09.008

May, R. M. 1977. Thresholds and breakpoints in ecosystems with a multiplicity of stable states. Nature 269(6):471-477. https://doi.org/10.1038/269471a0

Meijer, M. L. 2000. Biomanipulation in the Netherlands: 15 years of experience. Thesis. Wageningen University, Wageningen, Netherlands.

Meng, X., Q. Lin, Y. M. Zhang, L. Y. Li, W. Jiang, and Y. G. Liu. 2014. Effect of salt stress on germination of wheat and screening of salt tolerance indices. Acta Agriculturae Boreali-Sinica 29(4):175-180. [Translated from the Chinese.]

National People’s Congress of PRC (NPC). 2010. The Soil and Water Conservation Law of the PRC, 2010.12.25 Revised. [Translated from the Chinese.] http://www.gov.cn/flfg/2010-12/25/content_1773571.htm

O'Brien, K., and J. Barnett. 2013. Global environmental change and human security. Annual Review of Environment and Resources 38(2):373-391. https://doi.org/10.1146/annurev-environ-032112-100655

Peng, Y. S., Y. W. Zhou, and G. Z. Chen. 2008. The restoration of mangrove wetland: a review. Acta Ecologica Sinica 28(2):786-797. [Translated from the Chinese.]

Qin, B. Q., W. P. Hu, G. Gao, L. C. Luo, and J. S. Zhang. 2003. Dynamic mechanism of sediment suspension and conceptual model of endogenous release in Taihu Lake. Chinese Science Bulletin 48(17): 1822-1831. [Translated from the Chinese.] http://dx.doi.org/10.3321/j.issn:0023-074X.2003.17.002

Qin, Z. D. 1977. The unique natural environment and rich natural resources of the Qinghai-Tibet Plateau. Resources Science 1(1):35-39.

Qiu, J. 2012. Chinese survey reveals widespread coastal pollution. Nature. https://doi.org/10.1038/nature.2012.11743

Ratajczak, Z., S. R. Carpenter, A. R. Ives, C. J. Kucharik, T. Ramiadantsoa, M. A. Stegner, J. W. Williams, J. Zhang, and M. G. Turner. 2018. Abrupt change in ecological systems: inference and diagnosis. Trends in Ecology & Evolution 33(7):513-526. https://doi.org/10.1016/j.tree.2018.04.013

Sasaki, T, T. Furukawa, Y. Iwasaki, M. Seto, and A. S. Mori. 2015. Perspectives for ecosystem management based on ecosystem resilience and ecological thresholds against multiple and stochastic disturbances. Ecological Indicators 57:395-408. https://doi.org/10.1016/j.ecolind.2015.05.019

Scheffer, M. 1990. Multiplicity of stable states in freshwater systems. Hydrobiologia 200(1):475-486. https://doi.org/10.1007/BF02530365

Scheffer, M., S. Carpenter, J. A. Foley, C. Folke, and B. Walker. 2001. Catastrophic shifts in ecosystems. Nature 413:591-596. https://doi.org/10.1038/35098000

Shi, Y. F. 2003. Glacier recession and leke shrinkage indicating the climatic warming and dring trend in Central Asia. Acta Geographica Sinica 45(1):1-13. [Translated from the Chinese.]

Shi, Y. F., Y. P. Shen, D. L. Li, G. W. Zhang, Y. J. Ding, R. J. Hu, and R, S, Kang. 2003. Discussion on the present climate change from warm-dry to warm wet in Northwest China. Quaternary Sciences 23(2):152-164. [Translated from the Chinese.]

Smith, P., L. Beaumont, C. J. Bernacchi, M. Byrne, W. Cheung, R. T. Conant, F. Cotrufo, X. Feng, I. Janssens, H. Jones, M. U. F. Kirschbaum, K. Kobayashi, J. LaRoche, Y. Luo, A. McKechnie, J. Penuelas, S. Piao, S. Robinson, R. F. Sage, D. J. Sugget, S. J. Thackeray, D. Way, and S. P. Long. 2021. Essential outcomes for COP26. Global Change Biology 28(1):1-3. https://doi.org/10.1111/gcb.15926

Song, M. 2017. From “fan city” to “compact city”: on the development of urban spatial morphology in Hefei. Thesis. Southeast University. Nanjing, Jiangsu, China. [Translated from the Chinese.]

Su, H., Y. Wu, W. Xia, L. Yang, J. Chen, W. Han, J. Fang, and P. Xie. 2019. Stoichiometric mechanisms of regime shifts in freshwater ecosystem. Water Research 149:302-310. https://doi.org/10.1016/j.watres.2018.11.024

Sun, K., L. Hu, J. Guo, Z. Yang, Y. Zhai, and S. Zhang. 2021. Enhancing the understanding of hydrological responses induced by ecological water replenishment using improved machine learning models: a case study in Yongding River. Science of The Total Environment 768(7):145489. https://doi.org/10.1016/j.scitotenv.2021.145489

Tang, L. L. 2015. The effect of different nitrogen application rate on paddy ammonia volatilization and ecological threshold of nitrogen input. Thesis. Nanjing Agricultural University, Nanjing, Jiangsu, China. [Translated from the Chinese.]

Tang, T., Z. Ren, T. Tang, and Q. H. Cai. 1016. Total nitrogen and total phosphorus thresholds for epilithic diatom assemblages in inflow tributaries of the Three Gorges Reservoir, China. Chinese Journal of Applied Ecology 27(8): 2670-2678. [Translated from the Chinese.] http://dx.doi.org/10.13287/j.1001-9332.201608.010

Toms, J. D., and M. L. Lesperance. 2003. Piecewise regression: a tool for identifying ecological thresholds. Ecology 84:2034-2041. https://doi.org/10.1890/02-0472

Turner, M. G., W. J. Calder, G. S. Cumming, T. P. Hughes, A. Jentsch, S. L. LaDeau, T. M. Lenton, B. N. Shuman, M. R. Turetsky, Z. Ratajczak, J. W. Williams, A. P. Williams, and S. R. Carpenter. 2020. Climate change, ecosystems and abrupt change: science priorities. Philosophical Transactions of The Royal Society B Biological Sciences 375(1794):20190105. https://doi.org/10.1098/rstb.2019.0105

Walker, B. H., J. M. Anderies, A. P. Kinzig, and P. Ryan. 2006. Exploring resilience in social-ecological systems through comparative studies and theory development: introduction to the special issue. Ecology and Society 11(1):12. https://doi.org/10.5751/ES-01573-110112

Walker, B. H., and J. A. Meyers. 2004. Thresholds in ecological and social-ecological systems: a developing database. Ecology and Society 9(2):3. https://doi.org/10.5751/ES-00664-090203

Wang, B., J. B. Han, Z. C. Zhou, Y. Dong, X. Y. Guan, and B. Jiang. 2014. Ecological thresholds of Suadea heteroptera under gradients of soil salinity and moisture in Daling River estuarine wetland. Chinese Journal of Ecology 33(1):71-75. [Translated from the Chinese.] http://dx.doi.org/10.13292/j.1000-4890.20131220.0001

Wang, B. S., B. W. Liao, Y. Q. Wang, and Q. J. Zan. 2002. Mangrove forest ecosystem and its sustainable development in Shenzhen Bay . Science Press, Beijing, China. [Translated from the Chinese.]

Wang, C. G., and D. M. Zhang. 1985. Characteristics of vegetation evolution in Lop Wasteland after Lop Nur Lake dried up. Arid Zone Research (1):14-18. [Translated from the Chinese.] http://dx.doi.org/10.13866/j.azr.1985.01.004

Wang, H. J. 2007. Predictive limnological researches on small-to medium-sized lakes along the mid-lower Yangtze River. Thesis. Graduate School of Chinese Academy of Sciences (Institute of Hydrobiology, Chinese Academy of Sciences), Wuhan, Hubei, China. [Translated from the Chinese.]

Wang, S. L., X. F. Zhao, D. X. Guo, and Y. Z. Huang. 1996. Response of permafrost to climate change in the Qinghai-Xizang Plateau. Journal of Glaciology and Geocryology 18:157-165. [Translated from the Chinese.]

Wang, W. K., Z. Y. Yang, D. H. Cheng, W. M., Wang, and H. B. Yang. 2011. Methods of ecology-oriented groundwater resource assessment in arid and semi-arid area. Journal of Jilin University (Earth Science Edition) 41(1): 59-167. [Translated from the Chinese.] http://dx.doi.org/10.3969/j.issn.1671-5888.2011.01.019

Wang, Y. R., J. Li, K. F. Li, and J. L. Rui. 2007. Hydraulic parameters of habitat requirement for fish in water reduced river reach due to diversion of hydropower station. Journal of Hydraulic Engineering 38(1):107-111. http://dx.doi.org/10.3321/j.issn:0559-9350.2007.01.016

Wu, F., S. H. Li, and J. M. Liu. 2007. Research on the relationship between urban green spaces of different areas and the temperature and humidity benefit. Chinese Landscape Architecture 23(6):71-74. [Translated from the Chinese.]

Wu, Q. X., X. D. Liu, H. Y. Zhao, Y. K. Wang, and B. Han. 1997. Analysis of runoff types and runoff critical precipitation in forest catchments. Soil and Water Conservation in China (4):32-33. [Translated from the Chinese.] http://dx.doi.org/10.14123/j.cnki.swcc.1997.04.011

Xu, H. L., Y. D. Song, and N. Aihemaiti. 2003. Effects of the ecological water input on grassland restoration at the lower reaches of Tarim river. Chinese Journal of Grassland 25(6):18-21. [Translated from the Chinese.]

Xu, Z. Z., Y. Luo, A. J. Zhu, and W. X. Cai. 2009. Degradation and restoration of seagrass ecosystem: research progress. Chinese Journal of Ecology 28(12):2613-2618. [Translated from the Chinese.]

Yang, D. D., J. Luo, J. She, and R. G. Tang. 2015. Dynamics of vegetation biomass along the chronosequence in Hailuogou Glacier retreated area, Mt. Gongga. Ecology and Environmental Sciences 24(11):1843-1850. [Translated from the Chinese.] http://dx.doi.org/10.16258/j.cnki.1674-5906.2015.11.014

Yi, Y. J. 2008. Impacts of changing flow and sediment on fish and habitat modeling of the Yangtze River. Thesis. Tsinghua University, Beijing, China. [Translated from the Chinese.]

Yi, Y. J., C. Q. Lin, and C. H. Tang. 2020. Hydrology, environment and ecological evolution of Lake Baiyangdian since 1960s. Journal of Lake Sciences 32(5):1333-1347. [Translated from the Chinese.] http://dx.doi.org/10.18307/2020.0500

Yu, F. L., Z. Y. Chen, X. Y. Ren, and G. F. Yang. 2009. Analysis of historical floods on the Yangtze River, China: characteristics and explanations. Geomorphology 113(3-4):210-216. https://doi.org/10.1016/j.geomorph.2009.03.008

Yu, K. F. 2012. Coral reefs in the South China Sea and their record and response to Holocene environmental changes. Scientia Sinica (Terrae) 42(8):1160-1172. [Translated from the Chinese.]

Yu, K. J., Q. Qiao, D. H. Li, H. Yuan, and S. S. Wang. 2009. Ecological land use in three towns of eastern Beijing: a case study based on landscape security pattern analysis. Chinese Journal of Applied Ecology 20(8):1932-1939. [Translated from the Chinese.]

Zhang, J. H. 2014. The variation of biodiversity of macrobenthic fauna with salinity and water depth near the Pearl Estuary of the northern South China Sea. Biodiversity Science 22(3):302-310. [Translated from the Chinese.]

Zhang, L. L., Q. Y. Han, Y. F. Shi, and M. Q. Zhao. 2018. Synergistic effects of eutrophication and salinity on biomass and carbon and nitrogen contents of Zostera japonica. Marine Sciences 42(12):55-61. [Translated from the Chinese.]

Zhang, Q., C. J. Zhang, H. Z. Bai, L. Li, L. D. Sun, D. X. Liu, J. S. Wang, and H. Y. Zhao. 2010. New development of climate change in Northwest China and its impact on arid environment. Journal of Arid Meteorology 28(1):1-7. [Translated from the Chinese.]

Zhang, Q. M., S. Z. Sui, Y. C. Zhang, H. B. Yu, Z. X. Sun, and X, S. Wen. 2001. Marine environmental indexes related to mangrove growth. Acta Ecologica Sinica 21(9):1427-1437. [Translated from the Chinese.] http://dx.doi.org/10.3321/j.issn:1000-0933.2001.09.005

Zhang, R. S., Y. M. Shen, L. Y. Lu, S. G. Yan, Y. H. Wang, J. L. Li, and Z. L. Zhang. 2005. Formation of Spartina alterniflora salt marsh on Jiangsu Coast, China. Oceanologia et Limnologia Sinica 36(4):358-366. [Translated from the Chinese.]

Zhang, S. F., D. Hua, X. J. Meng, and Y. Y. Zhang. 2011. Climate change and its driving effect on the runoff in the “Three-River Headwaters” Region. Acta Geographica Sinica 66(1):13-24. [Translated from the Chinese.] http://dx.doi.org/10.11821/xb201101002

Zhang, S. M., A. Rehanguli, Y. J. Zhu, X. W. Ma, and X. Y. Luo. 2016. Study on phosphorus threshold of spring maize in Akesu. Xinjiang Agricultural Sciences 53(3): 455-460. [Translated from the Chinese.]

Zhang, T., Y. J. Zhu, and X. B. Dong. 2017. Effects of thinning on the habitat of natural mixed broadleaf-conifer secondary forest in Xiaoxing’an Mountains of northeastern China. Journal of Beijing Forestry University 39(10):1-12. [Translated from the Chinese.] http://dx.doi.org/10.13332/j.1000-1522.20170187

Zhao, X. 2013. Threshold analysis of nutrient quality of the Pearl River Estuary based on aquatic biological evaluation. Pages 1294-1301 in 2013 Chinese Society for Environmental Sciences Annual Conference, Kunmin, Yunnan, China. [Translated from the Chinese.]

Zheng, D., W. H. Li, Y. P. Cheng, and J. Z. Liu. 2005. Relations between groundwater and natural vegetation in the arid zone. Resources Science 26(4):160-167. [Translated from the Chinese.] http://dx.doi.org/10.3321/j.issn:1007-7588.2005.04.027

Zheng, F. Y., G. L. Qiu, H. Q. Fan, and W. Zhang. 2013. Diversity, distribution and conservation of Chinese seagrass species. Biodiversity Science 21(5):517-526. [Translated from the Chinese.]

Zheng, Z. G. 2003. The influence of temperature and light on grain filling, dry matter production of Rice. Journal of Beijing University of Agriculture 18(1): 13-16. [Translated from the Chinese.] http://dx.doi.org/10.3969/j.issn.1002-3186.2003.01.004

Zhou, M. J. and M. Y. Zhu. 2006. Progress of the project “Ecology and Oceanography of Harmful Algal Blooms in China”. Advances in Earth Science 21(7):673-679. [Translated from the Chinese.] http://dx.doi.org/10.3321/j.issn:1001-8166.2006.07.003

Zhu, B. B., Z. B. Li, P. Li, and Z. You. 2010. Effect of grasss coverage on sediment yield of rain on slope. Acta Pedologica Sinica 47(3):401-407. [Translated from the Chinese.] http://dx.doi.org/10.11766/trxb200903180105

Zhu, C. Y., S. H. Li, P. Ji, B. B. Ren, and X. Y. Li. 2011. Effects of the different width of urban green belts on the temperature and humidity. Acta Ecologica Sinica 31(2):383-394. [Translated from the Chinese.] http://dx.doi.org/10.3969/j.issn.1000-6664.2012.01.024