Tree lessons from the world for sustainable cities

Trees are nature’s best protection mechanism against the impact of climate change. It is no longer a choice between the built environment in cities and tree-lined green spaces. The benefits of trees, amidst the brown and the concrete, are undeniable. They absorb carbon dioxide, offer shade besides fruits and flowers, hold water in the soil to improve groundwater levels, and thereby help mitigate the effects of changing climates, improve air quality, and mental health. 

Tree-rich cities are different from green cities; the latter takes many steps from greening construction and transport to building bike lanes, reducing emissions, and increasing open spaces to become carbon neutral and sustainable. Maintaining the tree cover and increasing its footprint are a part of the green city approach. Copenhagen, Amsterdam, Oslo, Frankfurt, Zurich, Vancouver, Portland (United States of America), and Curitiba are among the top green cities of the world. 

Of these, Amsterdam announced, in 2019, the removal of more than 11,000 parking lots to plant trees, Geneva has nurtured around 40,000 trees and 70 hectares of woodland including rare varieties of plants, and Frankfurt has an area called The Stadtwald or a city forest of around 5,000 hectares. Less known are Durban which has the KwaZulu-Natal, or the Garden Province, with almost 23.7 percent canopy of tree cover, Sydney has pledged to plant at least five million trees by 2030 to boost the canopy cover by 40 percent, and Singapore is expanding green space so that 85 percent of residents live within 400 metres of a park. 

China’s ‘Forest City’
Back in 2017, the Chinese government began building a new city in the mountainous region of Guangxi, southern China, where all the buildings including schools, offices, homes and hospitals were to be covered in over 40,000 trees and one million plants. Called the Forest City, the ambition as envisioned by well-known Italian ‘green’ architect Stefano Boeri Architetti, was for the trees-plants to absorb 10,000 tonnes of CO2 and 57 tonnes of pollutants per year besides producing 900 tons of oxygen every year.^[1] The Forest City was to house 30,000 inhabitants, have an electric rail line and electric cars, and geothermal energy for air conditioning. However, construction began only around 2020 and the Forest City is awaiting completion.^[2]

China builds Forest City in Malaysia, it’s now a ghost city
The idea of a city full of trees and sustainable practices was taken to Malaysia by China’s largest property developer under the Belt and Road Initiative in 2016. Also called the Forest City – then a $100billion project – the plan was to build an eco-friendly green city with a golf course, waterpark, offices, bars and restaurants with the urban space housing nearly one million people. 

This year, eight years later, Malaysia’s Forest City stands a forlorn swathe of construction with barely any takers. “Only 15 percent of the entire project has been built and, according to recent estimates, just over 1 percent of the total development is occupied… In reality, Forest City’s isolated location – built on reclaimed islands far from the nearest major city Johor Bahru – has put off potential tenants and earned it its local nickname ‘Ghost City’.” The property developer faces debts of nearly $200 billion. The question remains: Who will use it.^[3]

Milan’s Library of Trees or ‘Biblioteca degli Alberi’
The derelict uncultivated brownfield adjacent to Garibaldi Station was used to store or host temporary events. Conceived in 2003 but completed only in 2018 by a group of architects, the Library of Trees project has become a new kind of a public park with 23 different species of trees, a botanical garden, an urban connector, an open campus for cultural events and a sports ground with “a penetrable layer over important underground infrastructure nodes, all in one”. 

The tree species are grouped in circles spread out across the park with each tree’s name and description integrated as text along the path. These tree circles, when fully mature, will form ‘vegetal pavilions’ providing shade and shelter. “Straight paths are drawn across the park to connect points of interest and surrounding areas to one another, creating a polycentric, grid-like network. This ‘web of paths’ creates a patchwork of irregular fields, a series of very different garden typologies. The planting for the various fields is carefully selected to – together with the biological pond and the trees – generate a dynamic and biodiverse environment throughout the seasons,” writes ArchDaily. The regeneration and greening of the space has reportedly smoothened traffic flow, reduced traffic noise, and improved pedestrian connections.^[4]

Canada’s green roofs
What began as a mandatory requirement by local laws in 2009 in Toronto has since spread. From heat moderation to saving water and helping grow fresh vegetables on the roofs of buildings, the green roof policy in major cities of Canada have helped to absorb and clean stormwater and carbon dioxide. “A 10,000-square-metre green roof can turn a building from a ‘heat sink’ into a ‘life-generating force’. There are so many side benefits to it besides emitting wonderful, clean air into the atmosphere from plants’ oxygenation,” explained green roof artist Terence McGlade in his piece in The National Observer. 

Canada’s cities have shown that green roofs atop buildings stay “substantially cooler” than the roofs of black asphalt which immensely helps to cool down the building. These roofs can also retain two-thirds of the rainfall they receive as the water goes through plants down into ground-level storm systems. “In Vancouver, a 1,850-square-metre green roof over the public library’s central branch grows drought-resistant bunchgrass and kinnikinnick,” said officials.^[5]

Syracuse, United States of America
Syracuse became the 40th city in the US to join Tree Cities of the World, an international network of cities by the Arbor Foundation and Food and Agriculture Organisation (FAO) to encourage best urban forestry practices. The recognition for Syracuse this year came in its third year of concentrated efforts to increase the green cover forestry efforts. The city’s forestry division manages 35,000 street trees and 10,000 park trees across 1,000 acres of parkland and 400 miles of road.

The initiatives throughout 2023 that helped it receive the recognition include “introducing a large-scale private property tree planting program in which, in 2022 and 2023, Syracuse distributed 800 trees to property owners; launching the first-ever block pruning program to maintain 3,000 trees annually on a seven-year rotation; hiring personnel dedicated to design, review and safeguard the integrity of the tree canopy; concluding a successful two-year vacant land management pilot program at 701 Tully Street with students; awarding a contract to modernise the city of Syracuse’s tree ordinance for the first time in 43 years.” The Arbor Day Foundation is the world’s largest nonprofit membership organization dedicated to planting trees.^[6]

Barcelona’s Master Plan for trees
Barcelona has placed its Master Plan for Trees 2017-2037 at the centre of local policies.^[7] The plan aims to conserve Barcelona’s tree heritage, increase tree cover in the city and improve the lives of its residents. By increasing the canopy of tree cover from 5 percent in 2017 to 30 percent, the Plan aims to address the urban heat island effect by increasing shade and humidity to cool the atmosphere and lower temperature during summers. It also guarantees that 40 percent of the tree species can adapt to climate change. Groundwater as a resource is also a focus point of this plan; it states that tree pits will be enlarged to improve the rainwater retention in the soil which increases the permeable surface area of the city. 

This plan targets the environmental, social, economic and health benefits of trees. The city aspires to also increase the animal biodiversity by increasing the number of trees. It highlights the positive effect that green infrastructure has on life expectancy and also in reducing health inequality. Trees can reduce sound pollution and eliminate atmospheric pollutants to improve air quality. In 2017, it was found that the city’s trees and bushes eliminated more than 305 metric tonnes of polluting compounds. The shade and improved microclimate because of trees reduced the need for air conditioning, slashing utility bills by $10 million annually.^[8] 

The Green Challenge in Mexico City
Mexico City’s Green Challenge called Reto Verde was initiated by the Ministry of Environment’s Green Infrastructure Directorate to increase natural public spaces and reduce the impact of climate change. The challenge focuses on nature-based solutions through conservation, rehabilitation and creation of new green areas around the city. It looks at the city’s rivers, forests and other natural spaces. Improving soil quality, creating gardens for pollinators, and seed management are also taken care of. Under this Challenge, the city monitors and collects data on trees, shrubs and herbs, and the people involved in these activities.

With over 30,000 participants, in over 170 interventions spanning all 16 city districts, Mexico City successfully planted more than 30 million trees, shrubs and herbs by 2020. The Challenge includes peri-urban areas too. This resulted in the opening up of new open spaces for leisure, and new forest areas. The Green Challenge has made green spaces more accessible to the citizens. It has brought people together to care about a cause, improving social ties. This has improved awareness about the environment and the importance of green spaces in cities. The Green Challenge has shown how different stakeholders like district governments, civil society groups and private companies are important to pull off changes of this scale.^[9]

Tbilisi’s reviving urban forest
The city initiated The Tbilisi Urban Forest project in 2020 with an aim to revive the almost-dead pine forest on Mtatsminda Mountain, a 700-hectare area characterised by steep terrain and rocky soil.^[10] The plan was to replant about 40 native and climate-adapted species. Along with this, the project aimed to improve campsites, hiking trails and protect the area from private development. 

Using indigenous trees consolidated the city’s connection to its surrounding ecosystem. This approach, unlike the other urban projects that use imported trees, also helped to reduce the project’s carbon footprint. In May 2021, it was reported that 10,765 saplings were planted as a part of this initiative.^[11] The project is still underway.

Seoul’s wind path forests
In 2020, Seoul Metropolitan Government along with the Korea forest service announced plans to create its first “wind path forests” to combat its air pollution crisis and help to circulate clean air, absorb particulate matter, and minimise the Urban Heat Island effect. The plan was to expand the forested area by planting trees close together along rivers and roads. This would create the wind paths for that clean cool air generated at night from Gwanaksan Mountain and Bukhansan Mountain can flow into Seoul.^[12]  

Plantings of pine and maple trees, wild cherry trees and oak trees will be planted to take advantage of their air-purifying qualities and ability to absorb particulate matter.^[13] The project which can become a landmark for green infrastructure – it is said to reduce the average temperature by 7 degrees in downtown Seoul.^[14] The Government found the need to expand sustainable efforts and climate sensitive infrastructure. 

Copenhagen’s urban sustainability
Copenhagen, Denmark, can easily be considered a leading model of urban sustainability through its excellent urban design models, one of them being the mandatory incorporation of green roofs in all newly constructed buildings since 2010.^[15]

In 2016, the Copenhagen City Hall agreed to allocate 3.7 million kroner^[16] of their budget to planting 23,700 new trees. The city has also been successful in reducing its vehicular emissions with around 62 percent of the city’s residents commuting to work or school by bike and almost one third of all journeys across the city are done with this mode of transport, as per a 2021 article,^[17] that called it the ‘green capital of the world’. 

Copenhagen is an example of how public institutions and spaces play an important role in making green spaces. Around a quarter of the city’s urban area is made up of green spaces like parks, lakes, coast or natural areas. While the city itself is located on the coastal islands, architects proposed a new take on public spaces with their project ‘Floating Islands’ which introduces a new archetype of urban space –  a “parkipelago” of floating islands, open and free to be used by an increasing number of boaters, fishermen, kayakers, stargazers and swimmers.’ The first floating island was installed in 2018.

Cover photo: A park in the middle of an avenue in Condesa, Mexico City./Wikimedia Commons