Urban trees clean the air, provide shade, provide habitats for wildlife and keep us grounded as we go about our day-to-day business, so they should be incorporated into urban plans and architectural designs. Street trees, specifically, have even more functions because they provide aerial corridors for wildlife and protect pedestrians. Councils in the UK have a legal responsibility to reduce or remove tree-related risks, but, often, too many trees are deemed to be cumbersome and felled before alternative courses of action have been explored.
Trees trap harmful particulate matter (PM) on their leaves and also disperse PM. Particulate matter consists of microscopic solids or liquids that are in the air. These particles originate from motor vehicles, factories, construction sites, and so on. When it rains PM is washed off leaves enabling them to trap a fresh load of particles. If left airborne, PM can be inhaled into the human body where it can potentially cause serious lung and cardiovascular diseases. Research has shown that evergreen trees are particularly good at capturing PM because they are in leaf all year round, so they can trap PM throughout the year, but they aren’t suitable for every townscape. Deciduous trees that are excellent at capturing PM include silver birch, elder and field maple. Furthermore, trees absorb the following common dangerous air pollutants through their leaves, bark and roots: carbon monoxide, nitrogen oxides, sulphur dioxide and lead. Thus, urban trees act as giant air filters by cleaning the air which enables us to inhale fresher air, hence, live healthier lives.
Mature trees provide shading which is particularly beneficial in the summer when the weather can be unpleasantly hot. In towns and cities hard surfaces, such as tarmac and concrete, collect a lot of heat when exposed to the sun, before releasing it gradually, so shade is particularly important in urban areas. Trees also help to cool the environment because moisture evaporates from within leaves, via transpiration, or from the surface of leaves which makes it so solar energy is being put towards converting water into water vapour, rather than warming the environment in general. In the winter, urban trees slow the wind so that houses and other buildings retain their heat. In this way, trees help to moderate the climate, which is good for our health and wellbeing.
Urban trees also beautify townscapes and capture carbon. Deciduous trees display colourful leaves in the growing season and exhibit majestic shapes in the winter months, while evergreen trees provide interest throughout the year. Another major benefit of urban trees is that they provide a significant barrier between the sky and the earth during storms, hence, reducing storm water runoff and mitigating – or even preventing – flooding. As a result, less pressure is put on drainage infrastructure. When drainage systems are overwhelmed water companies in the UK pump sewage into rivers to prevent damage to equipment and properties, so trees, and other green spaces, indirectly, help rivers to stay cleaner.
Lines of street trees provide a partial barrier between the road and the pavement, so they help pedestrians to stay safe. In addition, they provide a calming atmosphere, therefore reducing reckless driving. Trees also shield homes from noise, lessening noise pollution. Studies have shown that being able to see trees from the window tends to help us see through periods of convalescence and reduces blood pressure. All in all, they help to bring about peaceful neighbourhoods.
Trees are also good for biodiversity. Native species of urban trees, such as the English oak, are particularly valuable to wildlife, but non-native urban trees also tend to attract lots of creatures. For example, horse chestnut trees, which are originally from South Eastern Europe, provide lots of pollen for moths, butterflies and bees. Street trees that commonly line roads in the UK include sycamores, oaks, silver birches and London planes. These trees can provide aerial wildlife corridors to urban gardens, parks, and other communal areas, making journeys into urban landscapes more attractive.
Urban trees that are in the vicinity of homes may have special importance to local residents because they may link other habitats to their garden, add a bit of much-liked foliage to the backdrop of their garden or just look, smell or sound pleasant in themselves. Those who aren’t able to get around easily and contribute to the goings on in their communities, such as those who are getting older, often deeply treasure their gardens, and the surrounding foliage, so we must make sure quieter voices are heard by councils before urban trees are felled. It goes without saying, but it is an underappreciated fact that a large tree cannot just be put back into place once cut down, so rash decisions that are insensitive to the concerns of locals should never be made. At present, too often, the people who will be most impacted, and the gravity of their concerns, are ignored.
Of course, dead, or otherwise dangerous, trees should be cut down for public safety. However, healthy urban trees are often cut down unnecessarily, which can lead to entirely understandable objections from locals. Street trees sometimes crack pavements, lift kerbstones or cause other minor inconveniences. When this happens alternatives to felling, such as pollarding and root pruning, should be considered. Pollarding involves cutting back the upper branches of trees so that growth is kept in check, shading is reduced and fewer leaves are produced during the autumn. A recognition of the importance of preserving urban trees, wherever possible, should reach across political divides because they deliver considerable benefits to society.
More trees should be incorporated into our townscapes, because of the multiple benefits they provide. Innovative architects are incorporating trees into their designs. For example, The Bosco Verticale are two residential towers, in Milan, which provide extended balconies for a whole array of trees, including oak, beech, larch, olive, and cherry. The buildings were inaugurated in 2014, and they also incorporate numerous climbers, perennials, climbers and ferns, which help to create rich tapestries of foliage on the sides.
The mature trees that we see about today were often planted by those who knew they would never benefit from them themselves because the true benefits of trees only kick in after many years of growth. This intergenerationalism reminds us that we should be grateful to the environmental stewards who came before us and, in the same way, aim to pass on a pleasant world to those who follow in our footsteps. Areas that are devoid of foliage make us forget about the vital importance stable ecosystems play in our lives. In this way, urban trees keep us grounded.