When we think of trees, we typically think of lush forests or rural areas - not of bustling cityscapes, towns, or tarmac. Trees are often synonymous with forests, peace and quiet, and not busy, polluting cities.

Cities are generally problematic for the environment. Even though they occupy just 2% of land on the planet, they account for more than 70% of greenhouse gas emissions and over 60% of global energy consumption.
Urban planting promises the introduction of trees into these areas, introducing them to city parks, streets and walkways so that cities and towns can reap the benefits that come along with greater canopy cover and more green spaces. So, what are the benefits?

Photosynthesis

During photosynthesis, trees convert carbon dioxide and water into oxygen and glucose (sugars). In one season, a mature broadleaf tree can produce enough oxygen to allow 10 people to breathe for a whole year.

That same mature tree can absorb carbon dioxide from the air at a rate of 21.6kg per year. It’s estimated that over 2.4 million tonnes of carbon is stored in the urban trees planted in London.

As well as providing the oxygen that we breathe, planting and maintaining trees in cities has been found to improve air quality by filtering emissions from cars and other pollutants from the air. Indeed, studies have found that particulate levels on city streets with urban trees can be up to 60% lower than on streets without trees. Tree planting has been described as one of the most cost-effective ways of controlling CO2 and other pollutants. With the amount of pollution that we see in cities growing across the globe, urban planting is an excellent way to fight back against rising pollutant levels in the air.

Temperature

In cities, the air, surface and soil temperatures are almost always warmer than in more rural areas. This phenomenon is known as the Urban Heat Island.

Cities are warmer due to concentrations of structures, darker buildings, more developed grounds and substrates (such as cement, brick and steel) and fewer green areas. These man-made structures thus create pockets for heat to gather in. Darker colours and materials also absorb heat from the sun, which dissipates during the day, causing the surroundings to feel warmer. Trying to cool down in these hotter city environments, which will only get warmer as climate change continues to worsen, also causes more problems. Typically, we turn to air conditioners to tackle the heat, but whilst these cause internal temperatures to fall, the hefty use of electricity actually causes outside temperatures to soar.

Trees are able to provide shade and help to cool the air in these urban areas - reducing the need for air conditioning. One mature tree has the same cooling effect as 10 room-sized air conditioners, without the negative heating impacts on the environment.

As well as reducing the need for air conditioning, sheltered streets are cooler, more protected from the wind and encourage people to interact with a common adoration for nature, who are now able to comfortably stop to chat under the sheltered tree canopies on warmer days.

Water

During photosynthesis, trees also take in water through their roots. One mature tree can absorb up to 450L of water through its roots every day, and even improve water quality by filtering rainwater.

Historically, cities and urban areas were built on or near floodplains, valleys and waterways, as this was useful for trade and transport, but now is less relevant due to our increased use of air travel. However, we continue to build in these areas that are prone to flooding, while pulling up trees to make room for more development. Fewer trees in these areas can increase the likelihood of disastrous floods, which can be counteracted by urban planting.

Wildlife

Urban landscapes are often not kind to wildlife - removing green spaces to make way for new developments. Providing new green spaces through urban planting can help to support the species that have previously been excluded. Oak trees, for example, provide habitats for more than 257 species of invertebrates - that’s not even accounting for the birds, mammals, fungi and lichens that they also support.

Providing these canopies can create habitats for a variety of species - increasing the biodiversity of our grey city landscapes.

Safety and Social Benefits

Spending more time in nature, specifically around green places, has been linked to lower blood pressure and reduced mental fatigue (as covered in this blog post). Cities and urban areas are associated with higher levels of stress and stress-related health problems, as they’re often the places that most of us travel for work, are more densely populated, and expensive to live in. Urban planting and providing more nature-rich areas here can only be beneficial for wellbeing and physical health. A 10% increase in urban green space can postpone the onset of health problems, such as asthma, skin cancer and stress-related conditions, by up to 5 years. Trees have also been linked to improved concentration in people with ADHD, and they can also help to enhance learning skills and social functioning in children. (You can read more about the mental health benefits of nature more broadly here).

Feeling more connected to nature through greater numbers of green spaces also has some more unexpected benefits. Tree cover has been linked to increased feelings of safety. Research conducted in the USA found that areas with higher tree cover were linked to lower crime rates. Trees along streets and roads also help to increase road safety, as streets and roads look narrower, encouraging slower driving and providing a buffer between roads and pedestrians.

And an obvious benefit to urban planting - it looks nice! When thinking of cityscapes, we often think of polluted man-made landscapes devoid of all things natural and green. Urban planting is helping to reverse this. A study conducted in Washington, USA, found that people visiting cities were prepared to pay more to park in car parks that were landscaped with trees and greenery. These green urban spaces have also been used well during the ongoing coronavirus pandemic - providing access to green spaces and helping the well-being of those living in busy cities when they could not travel to urban areas.

Inspirational Green Cities

From the studies and evidence above, it’s obvious that planting and maintaining trees in urban areas is extremely beneficial.

Copenhagen in Denmark is noted by some as the greenest city on the planet for its commitments to becoming carbon neutral and adoption of clean public transport solutions. In 2009, the City of Copenhagen published their plans to create ‘pocket parks’ in unused areas and street corners, ensuring that all people who live in and visit the city have safe and easy access to green spaces. In 2015, this was followed up by their 5 principle tree policy, ensuring that all existing trees are preserved and that 100,000 new trees will be planted before 2025. As a result of this, 96% of people in Copenhagen now live within a 15 minute walk of a green space, and the city has been voted as the world’s most liveable city twice in the last decade. Copenhagen has recently been ranked as the 5th happiest city in the world in 2020, where high citizen satisfaction has been attributed to the growing number of green spaces.

The city of Singapore has canopy cover of 29.3% - the most tree covered city in the world. Singapore has over 2,000,000 trees planted in parks and along streets, and are still planting more! Through the OneMilliontrees movement, the city hopes to engage volunteers and wildlife groups who will plant and maintain new trees, bonding with nature and others that want to continue to ‘paint the city green’. The scope of these efforts could even stretch pass the city borders, as increased studying and surveying as a result of planting could have beneficial effects for endangered native species, such as the Sunda pangolin.

What can you do to help?

Next time you are in a city, look out for the trees and see if there are any local projects you can get involved with to help with new planting or tree maintenance. If you don't see any urban trees, or there doesn’t seem to be any planting plans near you, why not contact your local MP and get something started? Your initiative and willingness to volunteer your time will help the cities of our future.

By Emily Gilford - Blog writer and conservation storyteller

Concrete jungle: Why our cities need more trees