## 1 Introduction  
In urban areas, where more than half of the world's population lives, an urban ecosystem is formed in which natural and artificial spaces are intricately connected, and urban residents depend on the services provided by the ecosystem [1]. The ecosystem provides many services that help human beings lead physically and mentally healthy lives [2]. Ecosystem services (ES) are defined as the benefits [3,4] that humans obtain from nature and are mainly classified into supplying, regulating, supporting, and cultural services [2]. The quality of these urban ES is closely related to various urban forms, such as land cover, land use, buildings, infrastructure, population, location types, and scale of green areas [5; 6; 7; 8; 9]. Urban ecosystem components are more complex than those of natural ecosystems, thus even small changes can cause a chain reaction of imbalances in ES [10]. Therefore, in order to maintain a healthy cycle in an urban ecosystem, the relationships between ES should be understood in detail [11]. Numerous studies have analyzed the interrelations (trade-offs) between supplying, regulating, supporting, and cultural services, which are the most important aspects of ES [12; 13; 14; 15; 16; 17; 18]. Most of these studies emphasize the importance of harmony and balance with urban ES in increasing the benefits that human society can enjoy from urban ecosystem. In other words, sustainable conservation and maintenance of urban ecosystem is in effect possible through harmony and balance with urban ES [10]. Simultaneously, with humans recognizing the benefits of ecosystem, it becomes possible to create a virtuous cycle for ecosystem [2; 19]. However, with increases in urban development and human activities, natural ecosystems are being damaged, consequently causing deterioration and imbalance in urban ES [20; 21]. This causes negative effects such as reduction of animal and plant habitats, creation of urban heat islands, increased risk of flooding, and increased carbon emissions, which threaten the lives of urban residents. Such environmental problems have been mostly improved and focus on natural ecological space mainly distributed in the city without the consideration of the interrelationship between natural ecological space and humans [7; 22; 23]. Recently, efforts to solve these environmental problems have been increasing through socio-ecological approaches that emphasize the comprehensive interrelationship between natural ecological space and humans [24; 25]. The improvement of urban natural ecological space considering the characteristics of human society can contribute to the increasing of urban ecosystem services [26]. Therefore, spatial planning, including urban planning, urban design, and landscape planning, has been applied as a major means for creating a sustainable city [27; 28; 29; 30; 31]. In the case of South Korea, various policy-initiated projects have been undertaken to improve ecosystem supplying, regulating, supporting, and cultural services with an emphasis on regulating services [32]. Regulating services include climate and natural disaster regulating, which are the regulatory benefits provided through the cycle of elements in the ecosystem [2; 33]. In other words, ecosystem regulating services (ERS) are closely related to maintaining the safety of urban residents. In a recent questionnaire survey on the increasing importance of ES, which included 1000 respondents in South Korea, 67.6% answered that regulating services are the most important [34]. In particular, many studies have revealed that the elements within regulating services have a synergizing effect [12; 35; 36; 37; 38]. This effect means that improvements in regulating service elements, such as carbon storage capacity in the city, can also lead to flood reduction and heat reduction. Hence, maintenance of balance within regulating services is considered just as important as the balance among the aforementioned supplying, regulating, supporting, and cultural services of an ecosystem [39; 40].