Urban Green Spaces as an Effective Tool to Regulate Urban Climate and Biodiversity: Current Research and Challenges

1. Introduction

Urban green spaces (UGSs) are at the cutting edge of recent research, due to their ability to provide critical ecosystem services, and improve citizens’ quality of life and public health [1]. They are considered highly influential factors and effective means for adapting and mitigating climate change impacts in cities due to vegetation’s ability to regulate the local climate.

In recent decades, modern cities have had to confront longer, more frequent, and more intense droughts, increased temperatures, altered precipitation patterns, and more frequent and severe extreme weather events such as storms and heatwaves, etc., [2], which have an impact on urban green infrastructure (plant health, vegetation survival, and species composition, etc.) and can degrade the provision of significant ecosystem services, including air purification, temperature regulation, and stormwater management [3]. Ensuring the survival and the proper ecological functionality of urban vegetation is critical and requires adaptive measures that include the proper plant species and materials selection, the application of alternative sustainable irrigation schemes, the prevention of surface sealing, etc., [4]. Such strategies, where long-term climate predictions and cyclical risk assessments are aligned with urban planning and interventions, can render green infrastructure systems more robust to foreseeable climate-induced challenges.

Research related to urban plant diversity is increasingly found to be affected by urbanization, which generally encourages the growth of non-native and disturbance-tolerant species at the expense of native species [5]. Other research regarding urban plant biodiversity showed that urbanization influenced species composition and the diversity of species towards more non-native and disturbance-tolerant (rather than native) species [6]. UGSs are characterized by species with wide ecological tolerances, adapted to cope with habitat fragmentation and elevated temperature extremes [7]. Moreover, Kowarik [8] attributed urbanization to the loss of native plant species as a result of pollution, the sealing of the soil, the simplification of habitats, and the introduction of non-native ornamental species. Well-designed urban greening interventions consisting of native species and diverse vegetation structures can enhance biodiversity conservation within cities and provide a mechanism for habitat restoration [9].

The incorporation of UGSs in climate change strategies and governance in modern cities is often adopted to reverse the urban heat island effect, and is greatly encouraged by many world authorities, including the European Union [10]. However, our knowledge of the complex urban environment and its association with green infrastructure is limited. The scientific results of several studies are, in many cases, contradicted, underlining the need for further research and investigation.

To address these concerns, we organized the current Special Issue in the journal “LAND” under the title “Urban Green Spaces as an Effective Tool to Regulate Urban Climate and Biodiversity”, aiming to collect original research and review articles providing insights into the impacts of green spaces in the urban environment, and also to investigate the reverse effect of the climate and/or meteorological conditions on the growth and development of the urban vegetation on small or large time and spatial scales.

The main findings presented herein provide significant methodological innovations and meaningful insights into urban planning and management, enhancing our knowledge of the complex and challenging urban environment. It is worth noting that the articles in this Special Issue provide insights and practices from seven countries around the world, further addressing the importance of urban green areas as a universal issue for research and discussion.

The editors highly acknowledge the author’s contributions to our Special Issue through the submission of original and high-quality papers, and also wish to thank the Land Journal editors and reviewers for their assistance and support in processing the articles.

2. An Overview of the Articles Featured in the Special Issue

This Special Issue encompasses seven research articles covering central aspects of urban environmental research, focusing on the urban green area cooling effect and urban design, the biodiversity and habitat complexity of urban green spaces, ecosystem services, climate change adaptation, the assessment of climate change risks, and local community engagement and collaborative management.

2.1. Urban Green Area Cooling Effect and Urban Design

Acknowledging urban green spaces as a critical tool for mitigating increased urban temperatures, Núñez et al. (List of Contributions, 1) applied local entropy mapping, using satellite images, to study surface temperature changes in Mexico City during a heatwave and quantify the impact of urban parks’ cooling effect. The authors confirmed the localized cooling influence of the urban parks in the areas within their immediate vicinity; however, the extent of cooling presented high variability throughout the city, depending on the urban park size, location, and the spatial characteristics of the surrounding environment, underlining the role of urban design and planning in enhancing the effectiveness of urban green infrastructure’s cooling effects in cities.

In Greece, Proutsos et al. (List of Contributions, 2) studied the thermal and optical behavior of different materials (artificial and natural) in an urban green space during a strong heatwave. The authors suggested that the proper selection of materials in an urban green area is critical for the regulation of the urban climate and the mitigation of UHI, in order to design and create climate-resilient cities.

2.2. Biodiversity and Habitat Complexity

Cabon et al. (List of Contributions, 3) underlined the significance of urban green spaces in enhancing urban biodiversity, underlining, however, the importance of improving the structure of urban infrastructure to resemble natural habitats. The authors focused on arthopods’ taxonomic and functional composition and identified 136 species of spiders in 36 grasslands in Rennes (France). According to their findings, urban sites hosted species-poor communities of spiders tolerant of the intense urban heat island effect, unlike rural areas. In the urban green sites, species of a large size and sensitive to heat presented to decline. These differences are attributed to the impacts of urbanization, specifically the UHI and the warm urban climate, along with the loss of habitat complexity in cities, demanding the enhancement of urban infrastructure and the incorporation of complex habitat structures to improve their role in regulating the urban climate and biodiversity.

2.3. Ecosystem Services and Climate Change Adaptation

Egegård et al. (List of Contributions, 4) addressed the significance of nature-based solutions (NbS) and ecosystem services in urban climate adaptation, specifically in flooding, albeit identifying a critical limitation in modeling as an effective, user-friendly, and cost-effective tool against flooding events. In a case study in Gothenburg, Sweden, they employed an ecosystem service approach at different biophysical scales and in climate change scenarios and validated its effectiveness for designing and building climate-resilient cities.

The need for the proper planning and management of urban green infrastructure (UGI) was also addressed by Hanna et al. (List of Contributions, 5). Focusing on Zaragoza, a medium-sized city in Spain, Hanna et al. (List of Contributions, 5) evaluated the current conditions of UGI for carbon sequestration and temperature regulation. The authors studied two UGI groups with different ecological functioning (city and city plus peri-urban zone), also conducting alternative scenarios based on stakeholder consultation. They detected large differences in carbon sequestration and temperature regulation between the high- and low-ecologically functioning UGI sites located, respectively, in peri-urban and urban zones. They also suggested focused UGI restoration targeting high-ecologically functioning green spaces, tailored mainly to enhance carbon sequestration in peri-urban zones and to regulate urban temperatures in densely built zones.

2.4. Climate Change Risks

Although the significance of green infrastructure in the urban environment is well acknowledged, due to the provision of several benefits to citizens, its conservation and expansion are limited by various factors, including socio-economic and technical factors, as well as the strong constraints imposed by climate change and extreme weather events. Carter et al. (List of Contributions, 6) conducted a risk assessment of the low water availability in grassed areas of Greater Manchester, UK, and proposed a risk assessment methodology for urban green infrastructure planning and action for climate-resilient UGI sites and networks.

2.5. Local Community Engagement and Collaborative Management

Urban green infrastructure management is of critical importance for the sustainable and effective adaptation of cities to climate change. In the Netherlands, Romero-Muñoz et al. (List of Contributions, 7) examined four long-lasting approaches for the management of green infrastructure in four cities. The authors addressed the importance of collaborative management between municipal authorities and citizens for the sustainable planning and maintenance of urban green spaces, presenting successful paradigms based on shared management practices and active citizens’ participation.

3. Challenges and Future Perspectives

All studies included in the Special Issue entitled “Urban Green Spaces as an Effective Tool to Regulate Urban Climate and Biodiversity” underline the significance of urban green spaces as an “asset” in modern cities, providing multiple benefits for local communities, including urban climate regulation, urban resilience, and enhanced biodiversity. However, even though the importance of green infrastructure is widely acknowledged, our understanding of its performance in the urban environment is still limited. Urban planners, stakeholders, and policymakers are required to confront challenges in the proper design and management of urban green spaces considering several political, legislative, social, and economic attributes, in conjunction with the environmental stresses associated with climate change and biodiversity losses.

Future research should be enhanced and give answers regarding critical issues and challenges, including the impacts of urbanization on urban and peri-urban ecosystems, land use conflicts in cities, the impacts of climate change on citizens and urban green infrastructure, inadequate vegetation management practices, data and knowledge gaps, and socio-economic and political constraints, etc.

On the basis of these considerations, we are pleased to announce the second volume of our Special Issue under the title “Urban Green Spaces as an Effective Tool to Regulate Urban Climate and Biodiversity, 2nd Edition” by the journal “LAND”, available at https://www.mdpi.com/journal/land/special_issues/V3JTB8448G (accessed on 6 February 2025), which is now open for new submissions. The editors warmly invite scholars to contribute innovative research articles, case studies, reviews, or perspectives and participate in enhancing our knowledge of the functionality, management, and sustainability of urban green spaces for resilient modern cities.