Torbay analysis sets out economic case for investing more in existing tree stock

By Hannah Jordan Friday, 27 January 2012

First UK i-Tree Eco survey shows that larger trees provide greater quantifiable cost benefits in terms of pollution removal.

A mature oak was shown to return a cost benefit ratio of 1:4.7 whereas a smaller tree returned just 1:0.01 - image: Treeconomics

Protecting mature trees and planting larger species in the UK's towns and cities should be prioritised over planting small varieties, according to a report published this week.

See a copy of the Torbay Urban Forest report and Horticulture Week's in-depth analysis - The Value of Trees

The analysis of the first i-Tree Eco survey undertaken in the UK suggests that a greater proportion of larger trees in a city provides more benefits to the ecosystem in terms of pollution removal and carbon sequestration and storage, so greater resources should be provided to maintain existing trees.

Torbay's Urban Forest, published by partnership environmental group Treeconomics, stresses the value of not only increasing canopy cover through planting new trees but points out that the most effective strategy for increasing average tree size is to focus on preserving and managing existing tree stock so that they remain healthy into maturity.

The document urges policy-makers to take greater account of urban tree stock in their decision-making while the use of education, community engagement, planning policy and tree preservation orders are encouraged to address the reasons for potential loss of urban trees.

The i-Tree Eco survey, developed by the US Forest Service to assess the structural value and environmental benefits of urban trees, was carried out in Torbay last summer.

With a total of 818,000, the area has more trees per hectare than many US and European cities, the report says. But its trees are smaller, meaning that they provide less canopy cover and therefore less environmental impact than other comparable cities.

i-Tree's figures show Torbay's tree population has a combined structural value of £280m and an annual carbon storage value of £1.4m. Carbon sequestration and pollution removal are valued in the study at £172,000 and £1.3m respectively.

But this would be improved through better management, maintenance and planning of urban tree stock, the report suggests.

Treeconomics co-founder Kenton Rogers said more resources must be provided to help maintain the country's urban tree population: "All too often the tree officers just haven't got the resources to reinforce anything that is written in their arboricultural management plan.

"Planting trees can't just be about meeting numbers because it's no good if you go back three years later and few of them have survived. The real issue is in their ongoing maintenance and making sure that the trees make a proper contribution to the public and environmental benefit."

Torbay Council principal natural environment officer Neil Coish, who headed the survey, said the findings had not only secured an extra £25,000 in his budget but had affected the council's tree maintenance strategy.

"We're going back to the principle of putting the right tree in the right place. Rather than putting in more smaller trees, we are planting larger trees that will only grow to maturity in that space."

Coish said the reintroduction of pollarding on many of Torbay's old street trees would also help to prolong their lives and therefore their environmental benefits.

"This analysis has helped us secure extra budget and got us sitting at the right tables at the right discussions."

Torbay's Urban Forest is available at www.itreetools.org.