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Benefits of Trees in the Urban Environment

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Gorgeous trees and beautiful shades

Gorgeous trees and beautiful shade - Flickr

Trees are all around us in the countryside but we are normally not far from a tree even when we are in a city. The benefits of trees are often ignored or simply not understood. Here are some of the many benefits that trees provide society.

Trees provide shade

Trees provide shade for us all. Yes, ok, we live in wet and cold Britain but the shade provided by trees helps to keep you and your car cool throughout the year. They also keep your house cool in the summer and warmer in the winter by trapping the heat under the canopy. On hot days the shade of a tree can be a welcome relief in the city which can be 5 degrees warmer than the neighbouring countryside. It is called the urban heat island effect but trees help more than just providing shade…

Trees cool the air

When light falls onto a black or dark surface, such as the roofs and tarmac roads in cities, the energy is absorbed and the surface is heated. This causes the surrounding air to be heated and we end up with hotter air in the city. This heating effect is the main cause of the urban heat island effect

When trees absorb light and use the energy in photosynthesis to produce oxygen and, as the energy is used, it does not turn to heat. Trees therefore intercept light which would otherwise fall on asphalt causing temperatures to rise. But it gets better, trees can actually cool the air.

Trees take water from the air and use it for photosynthesis (the hydrogen from water combines with the carbon dioxide, CO2, to form carbohydrates in the form of glucose, which the tree uses/stores for energy. As the water molecule, H2O, looses its hydrogen atoms it becomes a free oxygen molecule, O2) but trees take more water from the ground than they need, this water is lost through the leaves and evaporates. As the water evaporates and passes through the air it cools the air in a process known as evaporative cooling.

They absorb pollution

Some species of tress are chosen as street trees because they are very tolerant to the pollution in city air. They are also able to remove CO2, pollution and other particles from the air. They also produce oxygen giving us cleaner, more oxygenated air in the city making the air healthier for us all.

Carbon capture – carbon sink

As mentioned above, as the tree photosynthesises it captures carbon dioxide from the air and converts this into carbohydrates. This carbon is then used by the tree to grow and live. Although some of the carbon is released back into the air much of the carbon is ‘locked’ into the tree’s timber, branches and roots. Again this removes carbon directly from the air making the city air cleaner.

They provide a screen

Trees can be used to screen unsightly views but they can also be used to reduce noise and pollution, particularly evergreen species. The can also provide shelter from wind and rain and prying eyes.

Help to prevent flash floods

Trees slow rain as it falls through the air, the rain is held on leaves slowing its progress to the ground. This allows soil more time to absorb the water. More importantly for the urban environment trees slow the water from running down the road and down the drain. This reduces the surge of water entering our sewers and can prevent flash floods. On steeper ground the tree roots tie the ground together to prevent landslides and stops river banks from washing away.

Habitat

Trees provide homes and food for many animals from birds and squirrels to insects and bats. Trees also provide wildlife corridors allowing animals to move from one green area to another.

Happiness

Trees make people happy and give a can reduce stress. They can soften the harsh urban environment and provide a connection to natural habitat. Many people enjoy walking in our forests and parks, spending time amongst trees. This was particularly evident in early 2011 when over half a million people signed a petition to prevent the sell off of Forestry Commission woodland.

Increased property prices

As a result of all these benefits properties areas with a high number of trees can have a value upto 20% higher than equivalent properties in areas with fewer trees.

 

If you know of anymore benefits of trees please let us know by using the comment section below

References and further reading

Why are leaves green?

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It is an age old question. Ok, its not as often asked as ‘why is the sky blue?’ but it is a question worthy of a decent answer.

To find the answer we have to go back to school. Remember when, in science class, you were told light is made up of different colour light combined. If you have a prism to hand you can split white light in to red and yellow and pink and green. Orange and purple and blue. I can sing a rainbow… (sorry got side tracked there). The range of colours you can see (red through to blue) are referred to as the ‘visible spectrum’ or visible range of colours. There are other colours (such as infrared and ultraviolet) but i won’t cover these here.

Now we need to change subject to biology, don’t worry I will try and keep it simple. Many plants, trees and algae absorb the suns rays to produce their own food, it is a remarkable process and is called photosynthesis. The key ingredient for photosynthesis to work is a chemical called chlorophyll, a type of pigment. When a tree photosynthesises (the same applies to anything which photosynthesises) it absorbs carbon dioxide from the air which is combined with water in a chemical reaction which produces sugar for the tree. This chemical reaction requires energy to take place and it is chlorophyll that  provides the energy needed for the reaction.

Now, back to the subject of light. When light hits an object some of the light is absorbed and some light is reflected. Some items absorb some parts of the visible spectrum better than others. In other words an item, such as my red candle, is able to absorb green and blue light but unable to absorb red light which is reflected. Because the red light is reflected it appears red in colour.Leaves are good at absorbing red and blue light and not very good at absorbing green light which is reflected, making the leaf appear green in colour. You now know why they appear green but this is only part the story.

Leaves are green because of chlorophyll, a chemical essential for photosynthesis

Many objects are the colour they are by coincidence or by man. My candle is red because it was made in a factory. Dyes and colouring agents were used to make it red but why are leaves green? We know why they appear green but we also know trees and plants need energy from light to photosynthesise. Surely it would make sense to absorb all the light, including green light) and reflect nothing (and be black in colour)?

We are starting to get a bit more technical here but please bear with me.

Remember we briefly mentioned how the light spectrum extends past the visible colours into infrared and ultraviolet? Well, chlorophyll works best with red and blue light in addition to infrared and ultraviolet light. Chlorophyll is useless at using the energy within green light which is why it is reflected. Chlorophyll is not alone within a leaf, it is joined by other pigments called carotenoids. There are over 600 know carotenoids, such as lutein (appears yellow in colour), and each carotenoid absorbs a different colour(s) of light. The presence of Lutein, and other carotenoids, is not obvious because there is so much chlorophyll but the carotenoids do change the colour of a leaf which is why we see leaves in different shades of green.

So, leaves are green because they are stuffed full of chlorophyll, a chemical which is great at absorbing red a blue light but useless at absorbing green light. Plants do contain other chemicals which do absorb green but as there is so much chlorophyll most of the green light is reflected.