Good Idea: Urban jungles

Who doesn't like trees? Nobody. Everybody likes trees. But some people really, really like trees. The staff of the Woodland Trust, for example.
“We need more native trees and woods in urban areas," insists the trust's report Greening the Concrete Jungle. "Stature and beauty" aside, trees have a positive effect on physical and mental health, they bring financial benefits to the cities where they grow and they are good for urban wildlife. They can even save lives, possibly.

The heatwave that hit Europe in 2003 killed 2,000 people in Britain alone, the argument goes, and cities get hotter than rural areas, because buildings retain warmth. But trees have the opposite effect: while shade from their branches cools people under them, evaporation from their leaves cools the air around them.

Researchers at Manchester University estimate that increasing the city's green spaces by 10 per cent could bring the city's temperature down by several degrees. Which might not have Mancunians cheering now, but once global warming kicks in, they might be a bit more grateful.

Before that happens, however, they might be pleased to know that the city's rainfall is being quietly managed by its plant life, which reduces water run-off: research indicates that tree cover in cities reduces the cost of drainage and other water management.

And, the Woodland Trust argues, albeit in a tone more hopeful than forceful, "there is strong evidence" that green spaces "promote inward investment by creating a more attractive environment for businesses and their staff". True or not, greenery is certainly good for city birds and animals.

Infrastructure covered, the report turns back to death. Poor air quality shortens 24,000 lives a year; trees absorb the filth. Without green spaces to walk in, city people get fat, lazy and stressed; trees help with that, too. There are reports that link greenery with reducing blood pressure, raising self-esteem and even controlling attention deficit hyperactivity disorder.

“It is vital that the government sets targets for new woodland," the trust concludes. Really, though? It seems unlikely to become a government Budget priority in these straitened times, whatever the long-term financial benefits. Besides, some of the report's claims are a bit shaky. All but 284 of those who died in the heatwave were over 75; trees would not have saved most of them for long. And with press accounts of bloodthirsty foxes attacking people in London, maybe being kind to urban wildlife isn't as valued as it might be.

All the same, just reading about sitting in the cool shade under a leafy tree seems to be having a positive effect on my mental health. Stature and beauty alone can be enough to do it.