Thankfully, there is a really exciting paper in the journal Ecological Modelling titled ‘Implementing and managing urban forests: A much needed conservation strategy to increase ecosystem services and urban wellbeing’ that contained a lot of those answers. It looked at a number of major cities, places like London, Beijing, Tokyo, Los Angeles, and a few others, and tried to assess the value that the humble tree provides.

The biggest benefit is air quality. In this paper, London gained £375m of value thanks to trees filtering the air of pollution from things such as diesel cars and buses. This would increase if more trees were planted, especially if they were placed next to busy main roads. Trees are living things and as such they grow. To grow they suck carbon dioxide out of the air and convert it into bigger trunks, stronger branches, and more leaves.

 

The trees in London sequester CO₂, which has a benefit of £11.9m per annum. But trees grow year on year, so the value of those trees, just from the value of the CO₂ that has been stored, is now £364m.

Trees provide additional shade, and therefore the amount of energy used to cool buildings in the summer is reduced if there are trees, a benefit of £0.7m. Trees also drink plenty of water, helping to prevent localised flooding especially if it rains a lot over a few days. This was assessed to have a value of £8.4m a year.

All these values are for the whole of London, and last time I checked London is quite big. In this paper they estimated London having 2906 square kilometres of land area. This means that the total value that trees bring to London is £184,000 per square kilometer, or about £37 per person.

But we could also plant more trees. London is estimated to have only 20 per cent tree canopy area in the city today, but that could be increased to 36 per cent. But that would probably mean removing the odd car parking space, or even building safer places for people to walk and cycle.

 

I’m sure some people are thinking that trees are expensive. However, for each £1 you spend on a tree you gain £2.25 return on that investment every year. A tree costs about £400, planted, staked and watered.

If we planted say a thousand trees, that would require a budget of £400,000 but after 30 years it would result in benefits of £27m. I think that is worth it. Perhaps we should surround Cambridge with a forest. Plant a few tens of thousands of trees.

In the last few weeks, I’d have been happy to cycle home under the shade of a full tree canopy rather than the blazing sunshine we’ve been exposed to.

Perhaps it is time for the Forest of Cambridge to surround the city. With cycleways through the forest of course.