Technology plays an important role in improving air quality but at the moment, all the evidence points to the enormous benefits of real trees on city streets. There is no question about which option is a favourite with city dwellers. A recent Cork City Council survey found that the vast majority (92%) of people want more parks and green spaces in the city while 89% want extra trees on city streets.

In the past three years, Cork City Council has planted 9,000 trees including oak, beech lime and rowan. Parks such as Fitzgerald Park, Sunvalley Drive and Ballinlough Park have been extensively planted and more trees are planned for the 70-acre Marina Park, while UCC has over 2,500 trees.

Planting urban trees is a vital investment in the sustainability of Cork City as it is increasingly threatened by climate. Here’s why.

While oppressive city heat is currently concentrated in southern and eastern countries in Europe, heatwaves are becoming increasingly common in northern countries and this trend is likely to accelerate in the coming years.

A study of 293 European cities (2021) found that planting trees can reduce land surface temperatures by up to 12C during hot summers and that temperatures in urban areas completely covered by urban trees compared to continuous urban infrastructure could vary by 25C or more depending on the latitude of the country.

Trees play a key role in filtering and purifying the air in cities, reducing pollution and improving the quality of the air we breathe. While robotrees provide inconclusive results in the open air, real trees are masters at removing pollutants and trapping dust and particulate matter. 

The evidence shows that they can remove more than half (60%) of particulate matter in the air, thereby reducing risk of respiratory illness and other health problems like cardiovascular disease that are sensitive to poor air quality.

A study by Nature Conservancy (2019) found that increasing tree canopies in cities by 10% can improve air quality by 8%, with even greater impact when planted in areas of high pollution. A good tree canopy also reduces city centre noise pollution.

Trees are a key element in addressing climate targets. A mature tree can sequester about 22 kg of carbon dioxide over a year. In 50 years, that amounts to one metric ton sequestered by one tree in its lifetime. 

Research from Nature (2019) estimated that global tree cover sequesters around 400 billion metric tons of carbon—about a third (30%) of the total carbon in the atmosphere—vastly more efficient than any carbon sequestration technology currently available.

Planting of trees in cities is a pivotal ingredient to the 15-minute city concept that has grown out of efforts to reduce car dependency while meeting climate targets and creating walkable, liveable neighbourhoods with access to nature. Paris has committed to planting 170,000 new trees by 2024 as part of its 15-minute city plan with co-benefits to both sustainability, air quality and community wellbeing.

Co-director of the Nature Based Solutions Institute and urban forestry researcher in Vancouver, Cecil Konijnendijk, launched the 3-30-300 rule for cities in 2021 to provide a rule of thumb for policy makers to promote green areas in cities. He suggests that every home should have access to:

• Three decent sized trees for every home; 
• 30% tree canopy cover in every neighbourhood;
• A public park or green space within 300 metres.

Professor Konijnendijk proposes that every citizen should be able to see at least three trees of a decent size from their window. Mounting evidence points to the importance of green areas that are nearby and visible for mental health and wellbeing. The covid pandemic further highlighted the real benefits of nature and the need for cities to strive for an abundant canopy.

The figure of 30% has repeatedly been found to be a reasonable threshold for tree canopy in cities—less leads to a predominance of cement and more would be impractical for city living. Creating greener neighbourhoods also encourages people to spend more time outdoors, socialising with neighbours in their own community. 

Many of the world’s most ambitious cities in terms of environmental sustainability including Barcelona, Bristol, Cambridge, Oslo, Sydney and Vancouver have set a goal of 30% or more canopy cover.

Barcelona has also encouraged citizen engagement in greening of the city with individuals and communities encouraged to plant greenery on walls and roofs. Citizen inclusion in achieving targets fosters collective belonging and solidarity within communities as well as allowing people to actively engage with achieving climate targets.

Glasgow proposed an ‘Every Person, Every Street, Every Community’ initiative aiming to plant at least two trees for every resident in the city. This further progressed to a more ambitious 10 trees for every person in the Glasgow City Region. Presented at COP 26 in Glasgow, the initiative was an opportunity for communities, schools, businesses and landowners to get involved and work collectively to improve their city whilst addressing climate and health targets.

A study published in the Journal of Physical Activity and Health (2015) found that neighbourhoods with higher levels of green space were more likely to engage in physical activity with green spaces providing opportunities for walking, jogging and other forms of exercise.

Mounting evidence points to the benefits of green spaces to mental health. People living in neighbourhoods with more trees and green spaces report higher levels of life satisfaction, less stress, higher levels of social cohesion and a greater sense of community. 

Children’s cognition and memory improve with exposure to green spaces, suggesting the impact of green spaces and trees on stress levels and improved opportunities for physical activity and play.

Urban green areas also provide a habitat for plants and animals, contributing to biodiversity and ecosystem sustainability.

In the introduction to the Master Plan for Barcelona’s Trees 2017-2037, the authors state that the city is facing major challenges in the 21st century in terms of improving its population’s health and comfort, emphasising the critical role that trees play in the life of a healthy city.

"Trees in the urban environment are living organisms that live with people and provide them with a physical and emotional connection to nature.

"For many people, trees are the fragment of nature that they have closest to hand, a living ‘neighbour’ who is present throughout their lives, contributing to a healthier and more habitable city. Among other things, they mark areas of community life and interaction, seasonal changes and the passage of time." 

Isn’t it time that Cork city valued our ‘neighbours’, the trees on our city streets and the multiple benefits that they convey to citizens, communities and climate?

• Dr Catherine Conlon is a public health doctor in Cork and former director of human health and nutrition, safefood