How much is that tree in your street worth? Or the one in the park where you walk the dog? Probably a lot more than you think: it could be a five figure sum.

An article in last week’s New Scientist looks at the ways in which a value is beginning to be put on trees, especially urban trees. As the article is behind a paywall, here are some extracts to give you the flavour.

What the Victorians didn’t know [about London’s giant Plane trees] was how bloody big they get … Nor could they have appreciated the true value of the trees, beyond their hardiness and handsomeness
. . .
[Now] “treeconomists” have begun to put a fair price tag on trees, accounting for the services they provide, from keeping our buildings cool to preventing skin cancer.
. . .
[But] trees come at a cost … they must be constantly looked after … particularly … in cities, where ageing or diseased branches can fall on people and property, and roots can break up pavements … [which is why] Sheffield has generated protests … with its chainsaw massacre of 5500 trees, with another 12000 at risk .
. . .
What is important is the trees’ economic benefits … an existing method … which focused on a tree’s aesthetic contribution to a landscape. This typically generated value … in the hundreds of pounds.
. . .
[A] new method, which attempted to capture trees’ worth as an amenity, taking into account their attractiveness and how they accentuate or diminish a sense of place … called Capital Asset Value for Amenity Trees (CAVAT), it starts by multiplying the cross-sectional area of the tree’s trunk by a unit price … that relates closely to what the tree costs to buy, and which goes up with inflation … augmented … to take into account the tree’s species, visibility to the public, local population levels, the size and condition of the leaf canopy, the suitability of the species for its site and the tree’s life expectancy.
. . .
iTree attempts to price up the environmental services trees provide. It combines local weather and pollution data with tree metrics – including trunk girth, species type, canopy size and sunlight exposure – to calculate the value of the services the trees provide. These range from the pollution they remove from the air to the carbon they store, and the run-off into the sewage system they prevent by soaking up rain.
. . .
[There are] four core benefits trees provide: soaking up air pollution, storing carbon, saving money on energy by shading buildings in summer and cooling them in winter, and avoiding the emissions associated with the production of that energy.
. . .
Treeconomics has used iTree and CAVAT to calculate the worth of urban trees across the UK … [in] Hyde Park [they audited] the park’s 3174 trees, including 1188 planes … iTree estimates, their environmental services are worth £208,916 per year. The bulk of this … is the “social damage” cost of the pollution the trees prevent.
. . .
Because the park is in such a densely populated area, and because the trees are large, visible and highly suited to their setting, the amenity value of all the trees there is huge: £52,378 on average for each London plane.
. . .
The next step [is] a tool to help plan tomorrow’s forests … iTree Species, allows an urban forester to rank the environmental services desired in a new planting scheme, including reducing air pollution, wind and ultraviolet light. After plugging in these characteristics, alongside the hardiness required to cope with local geography and weather, and the predicted mature size of the tree, the software produces a ranked list of recommended species.
. . .
If a lamp post falls down or is damaged, people expect it to be replaced – it should be the same for a tree … trees get larger and provide more value as they get older, meaning they need to be preserved, not replaced.

And that makes almost no mention of the importance of the biodiversity supported by many trees – everything from aphids and pollinating moths to crows, all feeding, and feeding off, each other.

No, trees are not valueless. And they can’t be instantly replaced. Planning authorities and developers please note – removing trees for your convenience, even if they are replaced with saplings, is just not OK.