Green Space in Cities: What’s a Tree Really Worth?

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By Alex Johnson at Green Futures

The Leyland Cypress is the ultimate privacy tree, spreading its evergreen leaves so thickly and quickly that neighbours end up in arms over restricted views. But what’s it really worth? The South Devon Borough of Torbay, where 14.5% of all trees are Leylandii, is determined to find out. Using open source software developed by the US Forest Service, the local council is calculating the value of its urban forest – not just the notorious suburban cypress, but grander trees, too.

It’s not an idle endeavour. Beyond their aesthetic value, trees provide vital ecosystem services: cleaning the air, managing rainfall, storing carbon, reducing noise pollution and stabilising temperatures. Take out a tree, and you lose a free service. But until now, little assessment of the financial burden caused by the damage or destruction of local trees has been undertaken in the UK.

Torbay Council’s Arboricultural Services team is using i-Tree Eco software to measure the environmental services and corresponding financial values of local trees. The project, a collaboration involving Forest Research and Natural England, collects data on the way trees:

• save energy: their shade cools buildings in summer, and offers some shelter from winter winds
• store and sequester carbon (and at what rate)
• reduce pollution through filtration.

It will also assess the ‘structural value’ of the trees, including the cost of replacement. The findings will be used to establish a UK-wide benchmark for valuing trees.

Initial findings have thrown up some big numbers. They suggest that Torbay’s 818,000 trees have a combined structural value of about £218 million. They store carbon at a rate of 4,200 tonnes a year, a sequestration service worth nearly £1.5 million in total.

According to Kenton Rogers, the lead consultant in the consortium, “the trees with the largest canopies deliver the most benefits, but here in Torbay – with its views of the sea – these are the trees especially vulnerable to developers”.

In the US, i-Tree Eco has already made its mark. A study valuing the ecosystem services of New York’s trees at $122 million a year prompted Mayor Bloomberg to back the planting of one million trees over a ten-year period.

Putting a price on natural resources may go against the grain for naturalists and aesthetes, but as Pavan Sukhdev demonstrated with The Economics of Ecosystems and Biodiversity study [see ‘Don’t know what you got till it’s gone’], financial costs represent a ‘bottom line’ which holds sway for communities, businesses and policymakers alike.

Read this article’s companion piece: The Decline of London’s Gardens

This article originally appeared in Green Futures, the magazine of independent sustainability experts Forum for the Future.

Image courtesy of King_Of_Clone on flickr