To comprehensively and chronologically reflect the research progress of the carbon sequestration function of urban green space ecosystems in the world, the internationally recognized authoritative database was used as the data source, namely, SCI-E (science citation index expanded) of the core collection TM of Web of Science. The retrieval method is as follows: TS=(“urban green space *” or “urban green land *” or “urban green infrastructure *” or “urban park *”) and “carbon sequestration” or “carbon dioxide sequestration *”); Document type: “article” or “review”; Period: 1900-2022 (retrieval time: 10 May 2023). Finally, after screening and analyzing the articles according to the title, abstract, and keywords, 723 valid papers were obtained.

This paper analyzed and visualized the number of papers published, keywords, author groups, publishing institutions, publishing journals, highly cited authors, and papers on the carbon sequestration research of urban green space ecosystems, and analyzed them with the help of CiteSpace 6.1 R6.

Compared with the carbon sequestration of forest ecosystems, the international research on carbon sequestration of urban green space ecosystems started late. In 2001 this field of research began to have relevant literature reports, while the study of forest carbon reserves appeared in the 1990s. The first international published literature was a research paper entitled “Carbon sinks and human freshwater dependence in Stockholm County” published in the Ecological Economics journal. Jansson et al. estimated the ecosystem areas required for accumulating the total emissions of CO₂ by the Stockholmer population. The paper accumulated the CO₂ emissions of the population in the County. The authors discussed the usefulness and limitations of their approach in relation to focusing on people’s dependence on functioning ecosystems for ecosystem service generation and in structuring guidelines for the management of these ecosystems (Jansson and Nohrstedt, 2001). From the time change in the number of papers issued, the international research on the carbon sequestration of urban green space ecosystems can be roughly divided into three stages: 1) Stage I the initial stage (2001-2010) where the research on the carbon sequestration of urban green space ecosystems was scarce. This was the result of the human understanding of carbon sequestration function of urban green space ecosystems being in its infancy. The research on carbon sequestration was mainly focused on forest, grassland, and wetlands within large regions. 2) Stage II (2011-2020). The research showed a slow upward trend. After the 20th century, the ecological function of the urban green space ecosystem had been recognized, and the research on the carbon sequestration function of the urban green space ecosystems was rapidly developed. 3) Stage III (2021-2022) was a period of rapid growth, where the growth rate of the literature was more than three times higher than the previous stage. After 20 years of development, the research on the carbon sequestration function of international urban green space ecosystems was still in the developmental stage. The total number of research papers published on urban green space carbon sequestration in various countries from high to low are as follows: China (226), United States (196), United Kingdom (55), Germany (41), Australia (41), Italy (39), Canada (38), South Korea (33), Finland (27) and France (26) (Figure 1). China and the United States accounted for 31.25% and 27.11% of the global total of publications, respectively, with both countries having significantly more publication than other countries. China’s first SCI paper on urban green space carbon sink research was a publication titled “Using a set of strategic indicator systems as a decision-making support implementation for establishing a recycling-oriented society—a Taiwan case study” published by Chang I C in the journal of Environmental Science and Pollution Research in 2005 (Chang et al., 2005). Since 2011, the number of published papers in China has fluctuated; however, is on the rise. In 2022, the maximum number of annual papers in the SCI database reached 44. A comprehensive understanding of the relationship between urbanization and induced carbon emissions is essential (Shi et al., 2019). Over the past few decades, China’s rapid economic development has led to soaring energy consumption and intensive CO₂ (Wang et al., 2014). As a result, studies related to carbon sequestration in urban green spaces are rapidly and continuously increasing in China.

The number of international papers on cooperation reflects the status and effectiveness of scientific and technological cooperation between different countries/regions (Edwards-Schachter et al., 2011). In this paper, the data files retrieved from the core collection database of Web of Science are imported into the bibliometric analysis platform (https://bibliometric.com/results.html, accessed time: 10 May 2023) to generate the scientific and technological cooperation between countries network map (Figure 2). A total of 73 countries in the world have participated in research surrounding the carbon sequestration of urban green space ecosystems. In terms of international cooperation, the cooperation between the United States and China was closer than that between other countries, followed by the United Kingdom and China. The data demonstrates that China and the United States attach great importance and heavily invest in carbon sequestration of urban green space research. From the number of SCI papers and the cooperation between countries, we can see that China, the United States, and the developed countries in Europe occupy important positions, thus, having a significant influence on urban green space carbon sequestration research. In general, African and developing countries account for relatively few. The study found that countries with stronger collaborative relationships have a higher number of publications. The United States, for example, has an extensive network of international collaborations and a high publication record. International cooperation has a certain regionalism (Zhu et al., 2021), and in this study it is clear that European countries tend to cooperate with the United States and Asian countries tend to cooperate within Asia.

CiteSpace software was used to generate statistics on the top 10 scientific research institutions according to their number of documents and centrality (Table 1). Among the top 10 institutions with the largest share of international publications, China 5), followed by the United States 2), Sigapore 1), Finland 1), and Denmark 1). Among the top three research institutions, the Chinese Academy of Sciences ranks first with 132 papers, Peking University ranks second with 39 papers, and United States Forest Service ranks third with 23 papers. From the number of papers published, Chinese research institutions have made great contributions to the field of urban green space ecosystem carbon sequestration research. In terms of the centrality (Means intermediary centrality, a measure of the importance of a node in the network) of the issuing institutions, the top three are Peking University (0.25), Chinese Academy of Sciences (0.11), and Beijing University of Civil Engineering and Architecture (0.11). Among the top 10 centers, China has 6 institutions, the United States has 2 institutions, and Denmark has 2 institutions. In terms of the number and centrality of papers, Chinese research institutions have made significant contributions. The study areas of these studies are all located in Beijing, the capital of China. As the economic and cultural center of the country, the balance between socio-economic development and environmental issues in Beijing has been a hot issue of concern (Fujii et al., 2016; Xu S. et al., 2017).

The cited frequency of a journal represents its academic influence (Zhang et al., 2022). This paper comprehensively evaluated the influence of publishing journals by combining the three indicators that include: the number of published papers, the total number of citations, and the average number of citations (Table 2). In terms of article number, the top three journals in the world are Urban Forest and Urban Greening, Sustainability, and Science of the Total Environment. In terms of the total number of citations, the top three journals in the world are Landscape and Urban Planning, Urban Forestry and Urban Greening, and Journal of Environmental Quality. In terms of the average number of citations, the top three journals in the world are Ambio, Journal of Environmental quality, and Ecological Applications. From the ranking of the three indicators of the number of publications, the total number of citations, and the average number of citations, the journals sponsored by China have not been listed, and this indicates that the international influence and recognition of Chinese journals need to be improved. The reason may be related to the Chinese scientific research evaluation system and the incentive mechanism. At present, Chinese science and technology journals are mainly evaluated by foreign SCI and other evaluation systems (Zhao and Hu, 2020). Compared to other developed countries, China’s international scientific journals were founded later and have lower international influence. China’s research evaluation system encourages scientists to submit to international high-level SCI journals, and the development of journals founded in China has been somewhat affected (Lu and Xue, 2019).

“Ecological benefit” refers to the beneficial influence and effect of nature on human production, living conditions, and environmental conditions (Pérez-González et al., 2021). The concept of ecosystem services is the interaction between human beings and the environment through a series of combinations of biological diversity and non-biological elements, thus, linking biological processes and functions (Semeraro et al., 2021). The relationship between urban form and measures of environmental quality and biodiversity potential can affect the ecological performance of the urban environment (Jamie et al., 2007). With the acceleration of urbanization and the change in urban climate and environment, the focus of urban green space research has shifted to an in-depth discussion of the solutions to urban ecological environment problems, and has made major breakthroughs in alleviating the urban heat island effect, protecting biodiversity, and mitigating rain and flood disasters (Bowler et al., 2010). Human wellbeing has been studied extensively concerning ecological benefits of urban green land. The benefits of green space for people’s health and wellbeing can be viewed as a positive correlation (Cohen et al., 2007; Tzoulas et al., 2007), in physical and mental health (Maas et al., 2006; Sugiyama et al., 2008). Pollution will change the phosphorus, carbon, and nitrogen in the ecological stoichiometry of terrestrial plants, affecting vegetation productivity, nutrient utilization rates, and carbon sequestration capacity (Hou et al., 2022). In recent years, relevant research tends to comprehensively explore the relationship between urban green space, the ecological environment, and the overall health benefits of resident use (Wolch et al., 2014). Studying urban green space, even small urban green space promotes ecosystem services in the urban landscape. For example, the increase in local vegetation density and leaf area was related to higher levels of ecosystem service provision in urban areas, such as air pollutant capture, carbon storage, and heat mitigation. Urban habitats with higher vegetation coverage and density provide more carbon storage and bring greater heat island mitigation benefits to residents (Davwas et al., 2016).

The focus of carbon sequestration in urban green spaces is to strengthen the construction and protection of urban ecology and green space, such as the construction of carbon sequestration in urban green spaces that include planting trees and grass (Yang et al., 2022). To maximize the carbon sequestration of urban green space, it is necessary to optimize the urban green space’s ecosystem layout, species allocation, and ecosystem management (Fang, 2021). In the study of carbon sequestration of urban green space, screening of high-capacity carbon sequestration vegetation was helpful for the construction of carbon sequestration. Some studies have screened out pioneer plants such as mold morifolium, cane grass, and wild grass, which have high carbon sequestration capacity under a low nitrogen demand and can gradually increase vegetation coverage in exposed areas (He, 2015). However, a problem that was easily ignored was the role of vegetation with high carbon fixation capacities. Hua et al., 2022 study shows, the carbon sequestration production efficiency of artificial forests was higher than that of natural forests; however, was not as effective as natural forests in carbon sequestration, soil conservation, water storage, and biodiversity protection (Hua et al., 2022). Biodiversity was closely related to community stability. Greenbelt communities with high carbon sequestration and low biodiversity may have worse carbon sequestration performance under extreme climate conditions, or even a reverse effect (Gatti et al., 2021). Some studies have also confirmed that carbon sequestration was positively correlated with tree species richness. The proportion of native trees in green spaces indicates that the biodiversity goal of increasing tree diversity provides carbon sequestration benefits (Belaire et al., 2022). Therefore, attention should be paid to biodiversity when constructing or researching the carbon sequestration of urban green space.

With the evolution of urban green space development stages and the emergence of new technologies, research on green space management and maintenance modes and methods as well as the evolution of green space spatial patterns has increased rapidly (Jansson and Lindgren, 2012; Nurbaya et al., 2016). The relationship between urbanization, urban green space, and the carbon cycle has attracted significant attention in recent years. Environmental managers need to design and manage urban ecosystems in a way that enhances the stability of green space and the harmony between humans and nature (McPhearson et al., 2016). Urbanization constitutes an important process of land use and land cover change, which has an impact on both land and wetland carbon pools. Large and concentrated carbon fluxes as well as rapid changes in carbon pools make cities a large and dynamic element of the global carbon cycle (Hutyra et al., 2014). Previous studies have focused on determining the characteristics of carbon sources or sink at the regional and global scales, while there are few studies at the local and urban scales, due to the mixing of anthropogenic and natural fluxes being more complex and difficult to observe independently (Hutyra et al., 2014). In the past two decades, the research and assessment of ecosystem services through remote sensing has increased significantly. The development of satellite image technology has improved its space, spectrum, radiation, and time resolution, enabling spatial-temporal observations as well as the classification and monitoring of the vegetation on the land surface (Angélica et al., 2022). Urban green space vegetation was more heterogeneous than natural forests. The growth environment also showed significant differences. Therefore, it was necessary to optimize the investigation methods applicable to the characteristics of urban green space carbon sequestration research.

There are few studies on carbon sequestration accounting methods specifically for urban green space, with most of the research methods being optimized by the forest, grassland, and wetland carbon sequestration accounting methods. The biomass method was mainly used to indirectly calculate carbon sequestration based on the change in plant biomass, which is currently the most commonly used method to calculate carbon storage (Xiao et al., 2022). The development of the model accounting method of urban green space carbon sequestration capacity was based on the leaf area index equation (Ren et al., 2018). The carbon footprint method can also be used for statistical analysis of the carbon sequestration capacity of urban green space (Xiao et al., 2022). The vorticity correlation method uses the principle of micrometeorology to monitor CO₂ concentrations, wind speed, and direction at a certain height above the forest land to obtain the amount of CO₂ fixed or released by the ecosystem (Valentini et al., 2000). The combination of geographic information systems (GIS) and remote sensing (RS) allowed for information spatial analysis integration. The remote sensing model simulation method was mainly used to obtain vegetation growth state parameters using remote sensing technology and information systems. The combination of the two combined with ground survey analysis was used to obtain the forest biomass. For example, the three-dimensional green volume of the city can be obtained by using satellite aerial photographs and computer simulation (Kong et al., 2007). The calculation of carbon sequestration capacity based on professional software has also been widely used, such as i-Tree, CITY-green, and other software (Yao et al., 2022).