Formal coordination mechanisms to oversee project implementation and decision-making (e.g., multi-stakeholder steering committees, working groups)

The 28th of October Street (28ης Οκτωβρίου) was one of the most neglected streets on the eastern side of Thessaloniki, completely devoid of trees despite its central importance. Additionally, the street suffered from severe flooding during heavy rainfall. In 2011, the Municipality of Thessaloniki, in collaboration with Konstantinos Zervas, the Deputy Mayor for the Environment, Quality of Life, and Free Space, proposed a redevelopment project aimed at transforming the street through the planting of trees and the installation of flower beds that would function as rain gardens (Refs 3, 5). This initiative was part of the "Integrated Green Cities" action, which falls under the European territorial cooperation program Greece-Bulgaria 2007-2013 (Refs 1, 2, 3, 6).

To achieve the dual goals of sustainable rainwater management and urban beautification, decorative trees were planted in specially constructed bioretention tree stands. These stands, along with the flower beds, were designed to collect rainwater, which would then be used to irrigate the trees along the road and the plants forming the rain gardens. Rainwater was gathered from the road surface, pavements, and the gutters of apartment buildings through these bioretention systems (Refs 1, 2). This sustainable water management solution significantly reduced rainwater runoff, improved water quality, and enhanced the area’s aesthetic appeal (Refs 2, 6, 7).

This mega-project is part of the Agenda for the Commemoration of the Bicentenary of the Independence of Peru (3). It is the new ecological lung of Ventanilla where families have free access to a meeting point where they can carry out sports, recreational, leisure and cultural activities (1, 2, 3). This park is the largest emblematic work carried out in Callao and one of the largest in extension at the national level, built in commemoration of the 200 years of independence (1, 2, 3). It was built on vacant land, where there was no possibility of meeting or recreation for the neighbours (1).
In addition to offering recreational spaces, it is a cultural work that seeks to teach the population about the history of independence, making the public space a commitment to a citizen-centred public policy with an intercultural approach (3). In addition, its financing was part of the second phase of the economic reactivation plan for public investment, encouraging local economic development and generating more than 1,300 direct and indirect jobs (3). This work is an investment of the Executive together with the Regional Government of Callao and the labour force of the municipality of Ventanilla (1, 2). Its facilities are freely accessible and will contribute to the social development and well-being of the citizens (3).
Inaugurated in 2022, it has cultural components, such as squares and amphitheatres, playgrounds, campsites and more than 30,000 m2 of green and blue areas (1).

Masthuggsparken is a planned park in the Masthuggskajen district, which is undergoing development and construction. The park will measure about 2000 m2, and serve as a green oasis and meeting place for locals. It will have ameneties such as benches and areas for play, and a noise barrier against a large nearby road. The park will connect to the adjacent square and street, making it accessible to visit. The street will be renovated to have more trees and plants, increasing green connectivity in the district. The park will be surrounded by trees and other plants, which are planted to promote biodiversity and be adapted to a changing climate [Ref. 1-5, 7]. The park is at a low point, where up to 800 m3 of stormwater will flow during heavy rainfall, reducing flood risk in the surroundings [Ref. 1, 2, 6]. The Masthuggskajen district has a sustainability program, establishing goals for green environments which the park will contribute to. Green areas should be accessible to the entire district and provide ecosystem services such as rainwater management, climate adaptation, biodiversity and recreation. The program was created by the City of Gothenburg in collaboration with construction companies active in the area and was supported by Citylab Action, a national competence program in sustainable urban development [Ref. 7]. The City of Gothenburg is the primary responsible for the park, which will be constructed between 2025 and 2026 [Ref. 1, 2, 4].

The "EnRútate por el Ambiente" initiative is a collaborative strategy implemented in Cartagena through a partnership between Ecopetrol, EPA Cartagena, and the Cartagena Refinery. The initiative aims to promote sustainable community development in neighborhoods adjacent to the refinery by addressing key environmental challenges such as pollution and the degradation of water bodies and green spaces. Its overarching objective is to improve quality of life through the promotion of sustainable practices and environmental stewardship (ref 5).
The strategy is structured around three programs. The first component focuses on the management of public spaces for recreation and environmental care. The second, Guardians of the Channels, seeks to empower local residents as promoters of water body conservation within their communities. The third program promotes the engagement of all community members, including schools and educational institutions, through participatory environmental initiatives (ref 1).

The South Hennepin Marsh habitat restoration project, located below the Grosse Ile Toll Bridge causeway, within the Detroit River's Trenton Channel near Grosse Ile, Michigan, aims to restore and protect one of the region's most critical wetland habitats. This emergent marsh, historically vital for fish and wildlife, has suffered significant degradation due to river currents, boat traffic, and winter ice flows. The project, identified as a priority in the 2002 Habitat Protection and Remediation report for the Detroit River, encompasses the restoration of over 1,000 linear feet of protective shoals and 20 acres of productive wetlands, home to various native plant species such as rushes and submergent macrophytes.

The primary goal of the project is to stabilize and enhance the marsh's habitat, improving conditions for fish, waterfowl, reptiles, amphibians, and other wildlife. Restoration activities include the placement of approximately 10,000 cubic yards of rock and soil to rebuild eroded shoals, installation of erosion matting, and re-establishment of native vegetation. Additional habitat features, including habitat logs, mudpuppy structures, and stone spawning beds, will provide crucial breeding and feeding areas for species such as walleye, northern pike, and lake whitefish.

The project also incorporates soft engineering solutions, such as fallen branched trees and strategically placed stones, to support pollinators, birds, and reptiles. Feasibility studies and design plans were completed by Environmental Consulting and Technology, with funding from NOAA, and construction was carried out by E.C. Korneffel Company beginning in 2021. The project reached completion in November 2022, successfully restoring the shoals and protecting the marsh from further degradation. These efforts have significantly enhanced habitat availability, ensuring the sustainability of the South Hennepin Marsh as a critical ecological site within the Detroit River system.
(Ref.1-4)

The project to revitalize the Huveaune River and its biodiversity is taking place in Aubagne, a city within the Marseille Metropolitan area. For a long time, the river received little attention, constrained by urbanization, and was even covered for several hundred meters. Urbanization and the construction of a road have made the floodplain more susceptible to flooding (Ref 2). The initiative aims not only to restore the Huveaune and its environment but also to strengthen the connection between residents and the river (Ref 1) while reducing flood risk as a critical objective (Ref 1).
The challenge is transforming the area into a higher-quality environmental space with resilient ecosystems. A diagnostic conducted during the project's design phase revealed the site's degraded state, including the presence of invasive species, steep banks unsuitable for riparian vegetation, poor waterway conservation, and disrupted ecological continuity (Ref 2).
Key actions include revitalizing the river and its biodiversity, removing artificial banks, and creating new meanders to give the river a more natural shape. Diversifying flow patterns will create habitats for aquatic and fish species by varying water heights and flow speeds. This involves increasing the river's sinuosity and varying the width of the minor riverbed (Ref 2). Additional steps include planting trees and shrubs adapted to the Mediterranean climate with low water needs (Ref 2). To bring residents closer to the river, plans include creating walking and cycling routes, sports equipment, educational panels, and useful visitor facilities such as benches, water points, and restrooms (Ref 3).

The Urban Oasis Playgrounds project focuses on creating a guide for green regeneration of playgrounds located all over Iasi by using natural climate solutions, with the potential for wider application beyond the city(1 to 6). The project's primary goal is to tackle pollution in playgrounds and address the overall lack of green spaces for children (1). This initiative is led by the NGO Civica in collaboration with the Municipality of Iași and the Architects Association in Iași (OAR) (1). The project secured €50,000 in funding after winning a competition organized by Raiffeisen Comunități, with support from the NGO "Asociația pentru Relații Comunitare" (2 & 3).
In addition to pollution, the project seeks to address other critical issues, such as the heat island effect and the proximity of playgrounds to risk-prone areas (1). The guide will be developed based on public consultations with Iași residents and a comprehensive study to tackle these concerns (1 to 7).
Currently, the first phase of the project is underway, involving assessments of various factors in playgrounds, including existing vegetation, shading, surface quality, infrastructure conditions, and pollution risks (4). These aspects are also reflected in a questionnaire distributed to the public, which gathers opinions on factors like cleanliness, noise exposure, thermal comfort, safety, and preferred natural green solutions (6).
The initiative aims to raise awareness about climate change, actively engaging the community in the process (4). Once completed, the guide will be presented to the municipality with the goal of being adopted as a standard for future playground developments (1, 3, 4, 6). The first phase of the project will regenerate a playground by planting trees and native vegetation (3).

The City of Seville has carried out four tree planting campaigns between 2020 and 2024, aiming to meet the goals of its Urban Tree Management Plan for Seville [Ref. 2-7]. The intervention as described here is based on the planting campaigns to date, but as the Management Plan spans from 2019 to 2039, more campaigns can expected in the future. The tree management plan aims to provide guidelines for the planning of trees in the city to maximise their value and minimize conflicts. As part of the process, the current state of the tree population in Seville has been evaluated. The management plan describes the ecosystem services of trees related to climate adaptation, biodiversity and public health. It also identifies challenges and conflicts that may arise due to urban trees and their management [Ref. 1]. The plan has a goal to increase the tree cover in Seville by 5 % over 20 years, which leads to the ambition of planting 5000 trees yearly and the tree planting campaigns over the last years. Between 2020 and 2024, about 1000-5000 trees have been planted each year [Ref. 1-5].

This initiative is a community-based urban greening effort targeting environmental and social co-benefits in Cartagena’s El Pozón neighbourhood. It involved the planting of 491 fruit and timber trees along a 1,500-meter linear stretch, covering nearly two hectares in the Terraplén sector of the neighbourhood. Led by the "Establecimiento Público Ambiental" (EPA), it was developed in collaboration with various stakeholders, including the Gerencia de Espacio Público, Guardia Ambiental, SENA students, the Police, and community members (ref 1, 2). The project's primary goal was to enhance the environmental quality and aesthetics of the El Pozón neighbourhood by planting trees that provide ecological benefits, such as improving air quality, reducing temperatures, and enhancing biodiversity. Additionally, the initiative aimed to foster community engagement in environmental conservation, particularly in raising awareness about the importance of protecting and maintaining nature. The community is also expected to take on the responsibility of maintaining the planted trees, promoting a sense of ownership and sustainable stewardship (ref 1).

The Recovery of Green Area on Avenida del Lago is a group of activities aimed at restoring and preserving the ecological integrity of green space within an urban setting. This project involves multiple stakeholders, including the "Establecimiento Público Ambiental" (EPA) Cartagena, "Fundación Verde Que Te Quiero Verde", Asopopa, and local businesses such as Crepes and Wafles and Centro Comercial Caribe Plaza. The primary focus is environmental restoration, sustainable urban mobility, and public space recovery (ref 1). The project aims to rehabilitate the degraded green spaces along Lago Avenue by enhancing urban greenery, restoring mangrove ecosystems, and improving public access and mobility. It also focuses on reducing pollution, preventing informal waste disposal, and raising environmental awareness among local communities and businesses. These activities align with broader efforts to promote ecological sustainability and enhance urban resilience (ref 1, 3). Since 2020, activities have included the planting of trees, mangroves, and other native vegetation in the green spaces of the avenue. Regular clean-up campaigns have been organized to remove solid waste, and community education programs have been conducted to promote environmental stewardship (ref 2). Previously, Lago Avenue was an area plagued by pollution and homelessness, and with the project, the intention is to gradually transform the area into a wooded area or productive park (ref 2).