International Research Trends on Urban Ecosystem Services

I. Introduction

The urban densification, mass production, and overconsumption have led to substantial resource and energy inputs, resulting in environmental pollution and contributing to a global crisis driven by climate change (United Nations Environment Programme, 2000). The ongoing process of urbanization has encroached on green spaces, which are vital for mitigating the climate crisis, leading to a decline in biodiversity (Pauleit, Ennos, and Golding, 2005; Goddard, Dougill, and Benton, 2013) As a result, urban societies have become increasingly disconnected from ecosystems, yet the demand for urban ecosystem services has steadily risen to reduce environmental burdens and improve citizens’ health and quality of life (Gómez-Baggethun and Barton, 2013).

In 2012, the experimental ecosystem accounting was established to continuously collect and provide data and information related to ecosystems for the conservation of biodiversity and natural capital, as well as to monitor the environment, as part of the System of Environmental Economic Accounting (hereinafter SEEA) (UN, 2014b). In 2021, the United Nations Statistical Commission adopted the SEEA ecosystem accounting (SEEA-EA) framework to actively promote ecosystem accounting, which complements the previously established experimental ecosystem accounting (UN et al., 2021). The United Nations (hereinafter UN), in enhancing the value of ecosystem services, established the Sustainable Development Goals (SDGs) from 2016 to 2030, including two of the 17 main goals aimed at the protection and restoration of aquatic and terrestrial ecosystems (UN Statistical Division, 2015). Ecosystem services, by utilizing the components of ecosystems, enhance human well-being and can strengthen the sustainability and resilience of urban environments pressured by climate change through the provisioning, regulating, cultural, and supporting services they provide (Boyd and Banzhaf, 2005). Therefore, to enhance urban ecosystem services, it is essential to understand the trade-offs and synergies among the diverse and complex ecosystem services (Song et al., 2023). While urban ecosystem services can serve as a means for sustainable and resilient urban planning, pursuing innovative pilot projects based on ecosystem services may be limited and carry risks. Therefore, it is necessary to establish a framework for safe urban design that accommodates interdisciplinary collaboration among various stakeholders and allows for the possibility of failure (Ahern, Cilliers, & Niemelä, 2014).

Therefore, this study aims to identify the trends and key topics in various research studies related to urban ecosystem services conducted internationally, in order to establish a foundation for supporting urban planning decisions that enhance citizens’ health, safety, and quality of life while also providing beneficial ecosystem services for other species, thereby creating a healthy and sustainable urban environment..

Ⅱ. Literature Review

2. Ecosystem accounting

The EC proposed the SEEA, a multipurpose system that integrates economic and environmental data to provide comprehensive statistics, accounts, and indicators on the interrelationships between the economy and the environment, as well as the accumulation and changes in environmental assets. This standard guideline aims to unify economic, environmental, and social data into a consistent framework for overall decision-making (UN, 2014a). In March 2021, at its 52nd session, the United Nations Statistical Commission adopted the SEEA-EA. This integrated and comprehensive statistical framework was designed to organize data on habitats and landscapes, measure ecosystems, and track changes in ecosystem assets, linking relevant information to the economy and other human activities (UN et al., 2021). The UN describes SEEA-EA in monetary terms to express the social contributions of ecosystems, making it easier to compare their contributions to social welfare with familiar goods and services. It is divided into five accounts: ecosystem extent, ecosystem condition, physical ecosystem service, monetary ecosystem service, and monetary ecosystem asset account <Figure 1>.

<Figure 1>

Connections between the ecosystem accounts(Source: UN et al., 2021)

Ⅲ. Data and Methodology

Ⅳ. Results and Discussion

1. Basic trends

According to the basic analysis of the bibliographic information of the collected research papers, the studies related to ‘urban ecosystem services’ began with a small number of publications in 2008, saw a sharp increase in the mid-2010s, and once again experienced a surge in the number of publications as we entered the 2020s <Figure 2>.

<Figure 2>

The number of papers related to urban ecosystem services by publication year

These studies have been conducted across various fields. Notably, it was found that the most research (496 cases) was carried out in the field of ‘Environmental Sciences & Ecology,’ followed by a significant number of studies (147 cases) in the field of ‘Urban Studies’. Regarding the UN’s 17 Sustainable Development Goals (SDGs), the largest number of research papers, 473 in total, were related to the 11th goal, ‘Sustainable Cities and Communities.’ This was followed by a substantial number of studies, 349 in total, related to the 15th goal, ‘Life on Land’ <Table 1>.

<Table 1>

The number of papers aligned with the UN’s SDGs

2. Research topics

From the bibliographic information of 620 research papers reviewed in this study, a total of 1,915 keywords were collected. Among them, 70 keywords were found to have co-occurred in five or more papers. Excluding the keywords used for the literature search, such as ‘urban ecosystem services,’ ‘ecosystem services,’ and ‘urban ecosystem,’ the relationships among the remaining 67 keywords were analyzed and visualized as a network using the ‘VOS viewer’ program.

1) Temporal changes in research topics

First, based on the average publication year of the bibliographic data, the temporal changes in research topics were identified. The results indicate that, shortly after the mid-2010s, research primarily focused on ‘urban ecology’ related to ‘carbon’ and ‘urban biodiversity.’ In the late 2010s, a transitional period, research trends were dominated by studies on ‘green infrastructure’ related to ‘urban trees,’ ‘urban greening,’ and ‘urban resilience’ from an urban planning perspective. In the 2020s, the focus shifted toward studies using remote sensing technology to assess ‘land use and land cover (LULC)’ in the context of climate change and to explore nature-based solutions.

<Figure 3>

Results of the analysis of the temporal changes in research topics by research period

In addition, it was found that during this period, studies on blue infrastructure related to services provided by water space were born following studies on green infrastructure.

2) Interconnectivity of research topics

The network analysis results indicated that among the 67 selected keywords, ‘green infrastructure’ showed a very strong link strength (hereinafter LS) with ‘cities,’ ‘nature-based solutions,’ and ‘urban ecology.’ A strong LS was also found between ‘urban ecology’ and ‘biodiversity,’ as well as between ‘urbanization’ and ‘remote sensing’ <Figure 4>. Overall, ‘green infrastructure’ emerged as having the strongest total link strength (hereinafter TLS). Additionally, the kewords such as ‘urban planning,’ ‘urban ecology,’ ‘urbanization,’ ‘cities,’ ‘sustainability,’ and ‘biodiversity’ were also identified to have high TLSs, indicating that they are key topics driving research in urban ecosystem services <Table 2>.

<Figure 4>

Results of the analysis of link strength between keywords through network analysis

<Table 2>

The Keywords wthin the top 10 rankings based high TLSs

3) The centralities of the topics

(1) Degree centrality

According to the analysis of degree centrality in the network composed of keywords from the research literature, among the research topics related to ‘urban ecosystem services,’ the keyword most directly linked to the largest number of keywords is ‘green infrastructure’ <Figure 5>. This indicates that many studies have been conducted to enhance the functions of ecosystem services by establishing the green infrastructure in urban areas. Additionally, ‘urban planning’ and ‘urban ecology’ were also identified as keywords directly linked to many other keywords. Notably, ‘urban planning’ was analyzed as a keyword that forms a direct and close relationship with both ‘urban ecology’ and the aforementioned ‘green infrastructure.’

<Figure 5>

Results of the degree centrality calculation for research keywordsWhere, the size of a node (circle) indicates the degree centrality of the corresponding keyword

(2) Eigenvector centrality

According to the eigenvector centrality analysis, which calculates centrality by considering the importance of surrounding nodes in addition to directly related nodes, the overall results appear similar to those of the degree centrality analysis. However, as shown in <Figure 6>, it is notable that the size of node corresponding to ‘urbanization’ is larger, indicating a higher eigenvector centrality value for this node compared to the degree centrality shown in <Figure 5>. This suggests that ‘urbanization’ is a significant keyword associated with other important keywords, highlighting its prominence.

<Figure 6>

Results of the eigenvector centrality calculation for research keywordsWhere, the size of a node (circle) indicates the eigenvector centrality of the corresponding keyword

(3) Betweenness centrality

According to the results of betweenness centrality analysis, which measures the mediating role that a node plays in forming a network with other nodes, the size of the node for ‘urbanization’ was found to be significantly smaller compared to the nodes corresponding to the eigenvector centrality analyzed above <Figure 7>. This means that although urbanization can be an important topic of research, its mediating role in linking other research topics related to urban ecosystem services is weak. On the other hand, ‘green infrastructure’ was found to be an important keyword in linking other topics as a mediating factor. Therefore, ‘green infrastructure’ was found to be the keyword with the highest centrality values across all three centrality indices mentioned above.

<Figure 7>

Results of the betweenness centrality calculation for research keywordsWhere, the size of a node (circle) indicates the betweenness centrality of the corresponding keyword

Particularly, if studies related to ‘environmental justice,’ which exhibit very low values in the three major centrality indicators, including betweenness centrality, are linked with studies on ‘green infrastructure,’ which demonstrate very high centrality values, and their direct or mediating influence is enhanced, it is expected that environmental policies could be developed to equitably provide urban ecosystem services based on green infrastructure to all citizens.

Ⅴ. Conclusion

This study identified the trends of studies related to urban ecosystem services, which were conducted in the international academic community to secure evidence-based materials supporting decision-making in urban planning aimed at realizing sustainable cities based on ecosystem services.

According to the basic analysis results, studies related on urban ecosystem services have been attempted in various fields, with particularly many studies conducted in environmental science, ecology, and urban studies. In relation to the UN’s Sustainable Development Goals, the studies have mainly been focused on ‘Sustainable Cities and Communities’ and ‘Life on Land.’ The aforementioned studies emerged in the late 2000s and surged in the mid-2010s. During this period, research primarily focused on urban ecology aimed at reducing carbon emissions and conserving urban species. From the late 2010s, studies increasingly centered on urban greening and building urban resilience through green infrastructure from an urban planning perspective. Entering the 2020s, studies began to focus on finding nature-based solutions to adapt to and respond to the climate crisis, using remote sensing technology via satellites to more accurately analyze urban land use.

The results of network analysis on the keywords extracted from the bibliographic data of these studies indicate that ‘green infrastructure’ is the most important topic addressed, with many studies focusing on establishing such infrastructure in cities to enhance ecosystem service functions. In particular, it can be inferred that this green infrastructure serves as a means of providing ecosystem services to solve problems arising from urbanization as a nature-based solution in urban planning. Therefore, in the process of developing environmental policies aimed at realizing sustainable cities, green infrastructure that supports ecosystem services should be actively introduced and utilized. Furthermore, cities should be regarded as integrated socio-ecological systems, and institutional policies should be activated from an urban ecological perspective to achieve environmental justice.

Acknowledgments

This research was conducted as part of the National Institution of Ecology’s research project, “Development of Policy Decision Support System based on Ecosystem Services Assessment” (Project No.: NIE-B-2024-03).

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