Scientists have discovered that trees could play a critical part in limiting global heating to 1.5°C. An ambitious worldwide programme of tree planting could potentially absorb up to two thirds of man-made emissions of carbon dioxide.

The report’s authors have mapped out globally where that planting could take place. Here in the UK, Manchester-based charity City of Trees has carried out a parallel activity to understand what part trees could play in helping the city region tackle climate breakdown and air quality and become more resilient to extreme weather.

The City of Trees team has carried out the most comprehensive i-Tree Eco survey so far undertaken in the UK, using specialist software, with results informing where there is potential to plant millions more trees. 

Tree economics

Data has been collected from more than 6,000 trees across Greater Manchester to help calculate the economic and environmental benefits trees provide, as well as highlighting that one million trees in the region are at risk from pests and diseases such as Ash Dieback and Horse Chestnut Bleeding Canker.

The results show that there are an estimated 11,321,386 trees with 15.7 per cent of Greater Manchester beneath tree canopy.

Greater Manchester’s trees act as a filtration system for harmful air pollutants – removing 847 tonnes of pollutants each year. They assist with excessive storm water, intercepting 1,644,415 cubic metres of storm water run-off per year. 

Added to this they sequester 56,530 tonnes of carbon each year and the current carbon of all the trees in the region is 1,573,015 tonnes.

The total annual economic value of air pollution filtration, storm water attenuation and carbon sequestration in Greater Manchester’s trees is £33,298,891.

Insightful results

The surveyors collected data such as tree species and the width, height and diameter and condition of the trees. The data is fed into i-Tree Eco software, which processes the information and provides insightful results about the economic value of trees, trees under threat and where there is potential to plant more. 

The i-tree software was developed by the US Forestry Service and adapted for use in the UK by Forest Research. Data from an i-tree survey can be used for making effective resource management decisions, developing policy and safeguarding towns and cities trees and green spaces.

They found that it would cost over £4.7 billion to replace all Greater Manchester’s trees; these trees produce 122,450 tonnes of oxygen each year; the most common species of trees in Greater Manchester are Hawthorn, Sycamore and English Oak

Laurence Adams is one of 57 tree surveyors, specially trained by City of Trees. Laurence worked in a small team with other surveyors, who were trained ecologists.

The teams were given allocated plots each day, in one geographical area and they would travel to the GPS points on the map and then survey all the trees in an 11.3metre radius around that point. 

Fascinating creatures

Laurence said:“Sometimes you would be in a suburban area and you would find street trees or you would need to access people’s back gardens to survey the trees there. 

“Other times the location might be on the edge of the motorway and you would have to find a way of surveying those trees – at one point as we were right on the edge of the M62.

“We took measurements such as tree height, the size and condition of the tree crown, the thickness of the trunks, the estimated age of the tree and species as well as, whether there was any other space around the tree to plant more.

“Sometimes the trees would be on their own but there were instances where teams would find a group of trees together which may take up to two days to survey.

 “Putting aside their environmental benefits, being around trees is also one of our best ways to re-connect with nature in the city and, speaking as a relative beginner, the more you learn about them, the more you realise what fascinating creatures they are. It’s really important that we share our streets and green spaces with them.”

City of Trees

City of Trees is a movement set to reinvigorate Greater Manchester’s landscape by restoring underused, unloved woodland and planting 3 million trees – one for every person that lives in the city region, within a generation. 

The charity delivers a range of projects working with schools and communities to plant trees, manage woodlands and create urban orchards.They carried out the survey to influence policy, protect existing trees and woodlands as well as identifying land where more trees can be planted and informing plans for the Northern Forest.

The Northern Forest is a government-backed plan to plant 50 million trees across the North of England, stretching from Liverpool to Hull, within 25 years. The Woodland Trust is working with City of Trees and other community forests to deliver the vision.

Tree strategy

The findings from the survey are informing the Tree and Woodland Strategy All Our Treesthat City of Trees is producing for Greater Manchester, which outlines the need for more trees in and around our towns and cities, making sure that trees are prioritised where they are needed most. The right tree in the right place will help to combat key environmental issues such as flooding and air quality.

All Our Treeswill make recommendations for managing woodlands to ensure they remain healthy, delivering benefits for generations to come, and enhance wildlife and provide habitats and refuges for wildlife particularly those species that are under threat

The strategy will also support Greater Manchester’s five-year environment plan and the city region’s spatial framework – the plan for homes, jobs and the environment.

Director of City of Trees, Jess Thompson, said: “Trees are essential to our towns and cities and provide a necessary carbon capture system. They are vital for our future health and resilience. With reports such as the IPCC clearly stating we need to plant more trees as part of a multilateral approach to climate breakdown, we need to act now and this survey has provided us with the information we need to do that.”

This Author

Bryan Cosgrove is the resilience coordinator at City of Trees. Bryan’s current focus is on modeling provision and the need for ecosystem services in the urban environment.