Trees can help save cities

Green Transition

Mayors who have recognised their responsibility to transform their cities into sustainable and inclusive environments often like to focus on new technologies and innovative solutions in their pursuit of carbon neutrality and green transition efforts. Sustainable energy sources, micromobility solutions, smart city infrastructure… these are all laudable high technology solutions that deliver results, help make cities greener, create new jobs and draw private investments. However, there is also a cheap and efficient solution for making cities greener in every sense of the word, and it’s literally millions of years old – around 385 million, to be precise.


We are, of course, talking about trees. In the case of cities, we are talking about the concept of urban tree cover, the number of trees influencing the city’s environment, its ecosystem, and even its microclimate. Long-term benefits of urban tree cover cannot be overstated – they improve nearly every facet of a city, and experts note urban trees can help cities achieve as many as 15 out of the 17 United Nations’ Sustainable Development Goals.


For most of the recent past, cities have readily sacrificed tree cover to expand physical urban infrastructure – buildings, roads, bridges, flyovers, car parks… modern developments regularly seen as key to cities’ prosperity. Since the beginning of the industrial era, urban tree cover has been steadily decreasing, with average tree cover decreasing by nearly 40,000 hectares per year on average during the past five years.


But with the cities facing rising temperatures, decreasing air quality, lack of communal areas and collapsing biodiversity, an increasing number of cities and their mayors are waking up to the fact that tree cover is cheap and highly effective solution to many of these problems, leading to introduction of projects aiming to preserve a minimum of existing tree cover, or even to expand it by planting new trees and designing new and reconstructed neighbourhoods to include more trees, parks and green and blue areas overall.


In the face of growing climate challenges, trees are an impressive natural cooler, alleviating heat-island effect by providing shade. This effect helps protect the citizens from extreme heat waves, but also has an economic benefit as well, reducing the overall energy consumption needed to cool down homes and offices.


According to Australian government-funded research, every 10 percent increase in urban tree cover can reduce land surface temperatures in cities by 1.13 degrees Celsius. Data from Lawrence Berkeley National Laboratory showed that late afternoon temperatures in cities can differ by as much as 3 degrees between downtown areas and the city’s parks.


Trees increase areas under shade, total moisture in the environment, induce cooling of air by evapotranspiration, and increase the percentage of sun radiation deflected. During summers, shaded surfaces can be cooler by as much as 25 degrees Celsius than unshaded surfaces, while evapotranspiration can lower peak temperatures by up to 10 degrees Celsius.


A single tree, within five years of its planting, can bring about 3% energy savings for one household in reduced cooling demands. Within 15 years, this figure grows to as much as 12% savings.


Trees are also carbon dioxide vacuums, storing CO2 from the environment to fuel their growth. Depending on its species, a single tree can help capture between one and 22 tonnes of carbon dioxide during its lifetime. Trees contribute to negative emissions and can help cities reach carbon neutrality goals faster.


Urban tree cover also makes cities healthier overall. Trees reduce, block or at least buffer air, noise and water pollution – all of which are increased in cities compared to rural areas. The World Health Organization warns that the majority of the global population currently breathes air exceeding WHO guidelines. The Organisation for Economic Cooperation and Development stresses that air pollution incurs costs on the economy, through sick days and medical expenses, which could amount to 1 percent of global GDP output.


A less tangible but nevertheless real benefit of urban tree cover is its role in addressing social equality and inclusion – citizens with easier access to green spaces or nature report better mood and higher motivation to exercise outdoors, as well as socialise within their communities. These factors contribute not only to the quality of life in cities, but can also help attract greater business opportunities. The World Economic Forum even cites research showing that increased street cover can increase property values by up to 15 percent throughout a city’s neighbourhoods.


Finally, a diverse and well-maintained tree cover helps protect overall biodiversity by providing habitats for animals, insects and other forms of natural vegetation, which further supports urban tree health. Trees can minimise soil erosion during heavy rainfall, and can also provide essential resources to people living in cities, from food to medicines.


According to the latest data provided by the European Environment Agency, green infrastructure in cities – which includes allotments, private gardens, parks, street trees, water and wetlands – currently covers an average of 42 percent of cities within the 38 European Economic Area countries. According to the Copernicus Land Monitoring Services, urban tree cover makes up for 30 percent of the cities within the EEA countries on the average.


Some capitals stand out more than others. Oslo tops the list in both urban tree coverage with 72 percent, and the overall green infrastructure with 77 percent. Ljubljana, Zagreb and Vilnius also made it to the top five on both lists.


The importance of tree cover is becoming increasingly recognised by mayors all over Europe, with ever more cities introducing reforestation and tree planting projects. In recent months, Warsaw announced plans to plant 500 new trees as part of an infrastructure project, after already planting more than half a million new trees since Mayor of Warsaw Rafał Trzaskowski took office.


In Madrid, Mayor José Luis Martínez-Almeida enlisted the help of citizens and businesses to plant 1.575 new trees, after already planting more than 130.000 plants as part of its 12-year Metropolitan Forest project.


Mayor of Seville Antonio Muñoz recently oversaw creation of the city’s first inventory of trees enjoying special conservation protection, aiming to preserve the city’s urban tree cover and put the city’s woodland heritage to the forefront.


The City of Toulouse recently also unveiled plans to plant 100,000 new trees by the end of this decade, after already planting more than 25,000 trees since the start of 2020. The Mayor of Toulouse Jean-Luc Moudenc also oversaw transformation of schools’ courtyards into urban oases by replacing asphalt with urban green areas, with plans to further expand them in the future.


According to the World Economic Forum, increasing urban tree cover is one of the best tools to help cities achieve Sustainable Development Goals, contributing to as many as 15 out of 17 UN goals. But maintaining the cover – ensuring urban trees reach their maturity and live a full life requires continuous efforts. WEF suggests that cities amend its laws to increase minimum urban tree cover area, avoid excessive use of concrete in public spaces, and to invest effort into relocating mature trees to open spaces, instead of bringing them down. Cities should also take greater care in urban planning not to destroy or displace its tree cover without sufficiently compensating for the losses.


Despite its age, urban tree cover is the solution of the future, and cities that wish to be both sustainable and inclusive will have to plan well, and tend and protect their islands of green in their urban areas.

(Photo credit: upklyak / Freepik)