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How green are city trees? Not as green as you think

Game Changers: The average tree newly arrived in a city takes 16 years to absorb its own carbon footprint

How green are city trees? It depends. A Swedish study recently found the average tree newly arrived in a city takes 16 years to absorb its own carbon footprint. Grown for years in nurseries, regularly root-pruned with fossil-fuelled machinery and transported by heavy machinery, the newly planted semi-mature city tree is, in carbon and biodiversity terms, a ghost replacement for a mature tree.

Worse still, in a privately landscaped area beside a new Dublin hotel, the labels on root-balled trees showed they had been grown in and transported from the Netherlands. Shipping in overseas trees makes no environmental sense. Long-lived trees in parks and leafy suburbs perform crucial work. They clean the air, cool streets in hot weather and help downpours permeate the soil with their deeply embedded roots.

It’s why the maintenance of mature city trees is vital. Technology can help with that. Dr Nadine Galle hosts the Internet of Nature podcast which highlights how sensors, 3-D mapping or smart inventories of street trees can help put a value on what trees do, and ensure they continue to do it for a long time. In a recent webinar, she interviewed a US arborist and a tech developer about how the two professions will collaborate in the future.

We need to look after urban trees and plant more. Doing all of it with semi-mature trees in cities is expensive and rapidly becoming unsustainable in volatile climate conditions. Root-pruned trees need staking for support so they don’t blow over. They need watering in drought conditions. Diesel vans carrying water tanks around in summer add to the carbon footprint.


So it’s great to see Dublin City Council trying something new. The council is part of a partnership for the Darndale Donut, which will see 3,000 much younger trees (bare-root whips) planted by the local community on December 1st. It’s part of a European urban forestry project called UForest, and brings together academics from Trinity College Dublin with a local north Dublin community.

“The goal is to provide the community with a green space to spend time together, enjoying nature and learning more about it,” the project organisers say. “The new forest will provide shelter from the wind to the adjacent fishing pond. To fully embrace this sense of inclusion and unity, the forest will be planted in the shape of a donut, where the trees will represent the outer ring.”

You can get involved by gifting or sponsoring a tree in the Darndale Donut for just €12, at The funding will help get the forest planted and pay for its upkeep. It promises to be a resilient model for reforesting in urban areas: native trees that start long healthy lives in urban areas and grow to be the pride of their local communities.

Catherine Cleary

Catherine Cleary

Catherine Cleary, a contributor to The Irish Times, is a founder of Pocket Forests