Objects Urban green spaces represent essential elements that enrich biodiversity, enhance the stability of urban ecosystems, and foster healthy community environments. Insufficient provision of green spaces can lead to the degradation of urban ecosystems, contributing to issues such as the urban heat island effect, pollution, flooding, traffic congestion, and increased prevalence of infectious diseases. Informal green spaces (IGS) encompass areas lacking formal management or maintenance yet effectively serving as green spaces. Various spatial indicators of IGS show significant correlations with ecosystem services (ES), offering valuable insights for evaluating the value of informal green spaces across different scales and urban interfaces. Exploring the ecosystem service value of IGS is a critical strategy for addressing the deficiency in urban green space supply and enhancing the quality of urban green areas within urban renewal. Examining the perceptions of different user groups regarding these services may well guide the enhancement of localized IGS and management strategies.

Methods This research takes Shanghai as an example. We examined how the city’s unique high-density urban land use characteristics can effectively manage informal urban green spaces within limited land areas, thereby enhancing the quality of green spaces in high-density urban environments. Firstly, based on high-resolution remote sensing imagery and on-site surveys, this research identifies and delineates six typical IGS in Shanghai. Secondly, based on The Millennium Ecosystem Assessment, relevant expert discussions, and literature surveys, a framework for the importance-performance analysis (IPA) of ES perceived by respondents in IGS is established. The differences in ES perceived by respondents within IGS are investigated. Thirdly, the research investigates users of IGS in Shanghai, with a focus on their demographic characteristics, IGS usage patterns, and perception of the importance levels and performance of four types of ES and the relationship between 12 segmented ES indicators and the six selected IGS. Finally, various analysis methods such as statistical analysis, importance-performance analysis, and ES index analysis are adopted to conduct both overall analysis and analysis based on respondent categories, with a view to quantifying the ES indicators perceived by respondents. Based on previous research, the abundance index and the Shannon’s diversity index are utilized to gauge the overall perception of ES indicators by respondents in each sample plot. The abundance index is defined as the total number of ES perceived by respondents in each specific IGS. In contrast, the Shannon’s diversity index is defined as the overall diversity level of ES perceived by respondents in each specific IGS. The research reveals differences in perceived ES indicators, such as abundance, diversity, and consistency, through the combination of overall assessment and specific analysis of different respondent groups and their relationships with different IGS.

Results Firstly, the research observes that the support services can be considered the most important ES with the highest performance and priority provided by IGS. Moreover, a significant proportion of respondents (63%) are quite familiar with IGS. Respondents report a low frequency of IGS usage, with 39% visiting IGS 1 − 3 times monthly. Each IGS visit lasts predominantly between 30 to 60 minutes (as reported by 39% of respondents). Among various activities, walking is the most common choice among respondents (78%), followed by family outings and camping (45% and 43%). Secondly, cultural and provisioning services are considered crucial ES with relatively low performance within IGS. The order based on the ranking of ES indicators as perceived by respondents is an effective way to implement IGS management improvements. Thirdly, across all sample plots, respondents typically rate the importance of each type of ES higher than their performance evaluation. These findings indicate that residents recognize the importance of various ES types that IGS can provide, but they are not entirely satisfied with the performance of the associated services. Finally, although all respondents believe that the abundance index of ES provided by IGS is relatively low, there are significant variations in their perceptions of IGS. Residents’ familiarity with IGS may greatly influence their access to and usage of IGS, especially for those with relatively poor primary conditions.

Conclusion Considering that humans are both the primary drivers of urban environmental changes and the primary target group for protecting or developing urban environments, the research focuses on residents’ perceptions to explore how residents in high-density urban areas in China interact with IGS and the impact of their perceived ES values of IGS on urban residents. Based on respondents’ bottom-up development and IGS usage patterns, the research estimates the perceived ES value of IGS from three dimensions: Importance-performance analysis of ES categories perceived by respondents, differences in ES indicators, and differences among respondent groups. This approach can help uncover the potential value and optimization directions of IGS. It is meaningful for optimizing and managing IGS by providing residents with perceived ES. Additionally, fostering urban residents’ understanding of IGS is crucial for unlocking the value of IGS in urban development. The research outcomes hold significance for optimizing and managing IGS to enhance residents’ perception of ES.