The role of the urban tree canopy in combatting climate change - Vol 3 Sneak Peek
Green is good: Author, Sally Smurthwaite, delves deep into the vital role that trees in urban environments play in helping to restore our planet.
Article by: Sally Smurthwaite
Artwork by: Leoni Fretwell
Many of us instinctively recognise that places with trees are more enjoyable spaces to be. Streets filled with trees are more welcoming and relaxing places to visit and live in. Most of us have a fondness for our local trees, standing sentinel as we get on with everyday life.
Urban tree canopies (UTCs), or the urban forests, are made up of individual trees (young to ancient) such as street trees, riverine trees, hedgerows, copses and trees in urban parks and woods. All of which have a hugely important role in making our towns and cities more liveable.
We are increasingly being affected by the impacts of climate change and these effects are particularly potent in urban areas. With over 80% of the UK population living in urban areas, it’s vital that we consider all options for mitigating the impacts including the unique role urban trees have to play.
Carbon storage
Climate change is caused by greenhouse gas emissions released by human activities such as burning fossil fuels, the biggest culprit being carbon dioxide (CO2). Trees can help us tackle the high levels of CO2 in the atmosphere by absorbing it through photosynthesis.
When trees absorb CO2 they store it in their leaves, branches and trunks in a process known as carbon sequestration. This carbon is then locked up in the biomass of the tree, potentially for centuries, reducing the amount of carbon in the atmosphere long term. Most of the carbon is stored in the leaves which is transferred to soil when the leaves fall and rot.
It is estimated that all the woodlands in the UK store around 213 million tonnes of carbon. A 2018 study found that the urban forest can store as much carbon as tropical rainforests. For example, Hampstead Heath in London can store up to 178 tonnes of carbon per ha, in comparison to tropical rainforests being able to store around 190 tonnes of carbon per ha on average.
This emphasises how important it is that we increase the urban tree canopy to sequester more carbon. However, mature trees absorb and store far more carbon than saplings, so using trees to tackle climate change needs to be as much about protecting the trees that we already have as planting new ones.
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