A few weeks ago, an SOS went out on the Islington Green Party email list - notices had appeared overnight on 14 trees in Drayton Park warning that they were to be cut down.
Nevertheless, the objectors won a temporary reprieve while the council mulled over the issue. That, in a nutshell, is the sorry plight of the urban tree, as highlighted in a recent London Assembly Environment Committee report into what it calls the “chainsaw massacre” of the capital’s seven million trees. It is a pattern of events repeated all over London. While councils are cutting down trees for fear of insurance claims; the public are unhappy with losing the greenery on its streets. To make matters worse, there is the difficulty of replacing the trees because of the tangled web of cables and pipes beneath roads and pavements competing for space with tree roots. The public is also too often guilty of being ready to claim compensation for subsidence by blaming trees and forcing timid local authorities to cut them down.
The cull of urban trees is a prime example of unjoined-up thinking at a time of increased awareness of their role in combating climate change. A recent study at Manchester University found that creating more parks and green spaces in urban areas could cool cities by up to four degrees Celsius – possibly enough to combat the warming from climate change. “If you look at infrared maps of cities, the woodland areas are 12 degrees cooler than city centres with no trees,” said Roland Ennos, quoted in New Scientist recently.
That is confirmed by Tony Kirkham, head of the arboretum at Kew: “Trees provide shade, putting a natural barrier between the sun and a human being. Not only do they absorb CO2, they also act like an air conditioner, cooling the atmosphere as the water they have absorbed is evaporated from their leaves.”
If you have a house with a large window facing south and a tree in front of it the room will be markedly cooler than if you took that tree out. Simple as that. Conversely, in winter it will provide extra warmth, its effect being that of a long, thick curtain. “The release of water vapour into the atmosphere also promotes cloud formation, and in addition, foliage, usually darker than the ground it grows in, absorbs heat from the sun.” Given that heat stress is likely to be the biggest health issue facing city dwellers in the UK as a result of climate change, preserving urban trees is vital. Researchers in Manchester found that the temperature in their city would rise by four degrees by 2080 if the amount of green space remained the same; but adding 10 per cent more green cover could cancel out that rise.
Tony Kirkham points to another very useful and lesser-known function performed by trees. “Their bark and leaves take in dust and grime and pollutants from the atmosphere and retain it. When London planes drop their bark, leaving a white surface, in that characteristic way, it is because this dirt and grime has built up so much they need to shed the bark in order to breathe. You will notice that the drier the summer, the more bark they will shed.”
Another effect of the councils’ capitulation in the face of insurance claims is a change of policy in the sort of trees planted. “The trees we want to see are what we call forest shade trees, such as oaks, planes and limes,” says Kirkham. “Unfortunately these are now being replaced by smaller ornamental trees, mainly of the rosaceae family: cherries, flowering crabs, rowans, birch, which have a life expectancy in cities of only 10-15 years. Small trees like this can’t hack the harshness of the urban environment, making them unsuitable as street trees. And because of their size they are less effective in the fight against global warming. But councils like them because they’re smaller and perceived as less of a threat.”
Kirkham also points to the psychological effect of trees, pointing out that the mere sight of greenery has a cooling effect. It has other benefits, too, as cited by the Tree Canada Foundation, whose researchers found that hospital patients with window views of trees recovered significantly faster and with fewer complications than comparable patients without access to such views.
Graham Simmonds, chief executive of Trees for Cities, says urban trees perform three important functions in the fight against climate change. They absorb CO2; they “moderate” the climate around a building, resulting in a 10 per cent saving on energy use; and thirdly they play an important role in diverting storm water. “As our climate changes, we are going to see more flash flooding,” he says, “which our drains just can’t cope with. Trees reduce the speed at which water is dissipated. It takes longer to reach the ground because leaves slow it down, rather like a big net. This is really quite significant. Instead of worrying about developing more sophisticated drainage engineering, the utility companies should be thinking about planting more trees.”
The London Assembly tree report clearly comes at just the right time, with urban trees under increasing threat but a burgeoning awareness of the necessity of saving them. It urges action from local authorities, landlords, developers and residents, not just to maintain but to increase the number of our city trees. As I write, I hear that the Drayton Park trees are to be felled after all. This report has come not a moment to soon.
Protect your local trees and woodland – if trees or woodland in your area are under threat you can join with others around the country in protecting them. The Woodland Trust, ‘Woods and Trees Under Threat’ website provides information on campaigning to protect your local trees and woods www.woodsunderthreat.info
