Vassili Papastavrou, BBC The Green Room 4 Mar 08;
Let's stop chopping of our urban trees and embark on a scheme to plant lots of fast-growing trees that soon leave us in the shade, argues Vassili Papastavrou. In this week's Green Room he tells us to take cover, because we need city canopies more than ever before.
While cycling to and from my home in Bristol, I have become aware of the large number of trees that are disappearing from surrounding streets.
A quick glance on Google Earth shows gaps like missing teeth along the once tree-lined avenues. It appears that a reason can be found to remove any urban tree.
Other neighbours shared my concern for the disappearing trees, so we looked in vain for an organisation that might help us; but there was none.
So, together we set up a local group called Bristol Street Trees. We also found out first-hand how nearly impossible it was to plant street trees in new locations, despite a huge willingness amongst the public to contribute money.
As we add to our collection of photographs of stumps, it seems that we are witnessing a dramatic loss of urban trees on public land, and street trees in particular.
Even if replacements are planted they are often species of tree that will not become large; the dramatic London planes are going, only to be replaced with rowans or flowering cherries, which will never provide the same benefits.
Though our interest is local, the problem is national. Scouring the press, we have found the most bizarre reasons for removing trees.
In Whitehall, street trees were removed as part of the "war on terror" and received global media coverage. In the London Borough of Islington, "killer pears" were given the chop.
In my local area, trees are removed for three main reasons: there are concerns about the hazards posed by "dangerous" trees, worries over often bogus subsidence claims, and road re-alignment projects which seem to require completely unimpeded sight lines, despite the slow crawl of urban traffic.
We live in a risk-averse society, but the danger from trees is tiny. Each year, about three people in the UK are killed by falling trees in public places, which works out as roughly a risk of one in 20 million.
The UK's Heath and Safety Executive considers a one-in-a-million risk as very low and the threshold for what is considered acceptable.
Contrast this with the risk of one-in-16,800 for an average Briton being killed in a car accident in any one year.
Take cover
The risks to our health and well-being from removing trees are far higher. The benefits that urban trees bring are only just being formally recognised.
We now know that they can reduce urban temperatures by 4C (7F); more urban canopy cover will be critical as temperatures climb as a result of global warming.
Trees also absorb floodwater and slow run-off and increase house prices. Studies in the US show they can even reduce crime rates.
Urban trees also absorb pollution of all kinds, particulate, chemical and noise; their ability to do this depends on their size.
The conflict between risk and benefit is a head-on clash between two major ideologies in a rapidly changing environment. Local councils are stuck in the middle, so no wonder their decisions are controversial.
In the case of an individual tree, only the problems it presents are considered; there is no mechanism to balance the benefits provided by the tree.
It is no coincidence that the biggest arguments happen over the biggest trees. Even ancient and veteran trees, some hundreds of years old, are under threat.
The very cavities and hollows that are seen as "problems" are important for woodpeckers, bats and other wildlife. Woodpeckers drum on dead wood, carefully choosing sounding boards that amplify the noise. But councils don't like dead wood - at least not outside their chambers.
Notable trees on private land are legally protected, as are all trees in conservation areas. In contrast, trees on public land have no protection.
Some councils do not even provide advance notice of tree removals, let alone consult residents. Days before one local tree was removed, a notice appeared on it saying: "Help, I need a solicitor".
Although there are many to make the case for the prosecution, it is Kafkaesque that no one can take up the defence.
The consequence is that the public is completely disenfranchised and watches powerlessly as trees are removed. We often hear of conflicts with tree officers, despite them sharing common values over the importance of trees.
Root of the problem
So what is the solution? Firstly, the discussion on risk that is already happening in the technical journals and industry conferences needs to be brought into the public domain.
Members of the public are quite capable of understanding risks - we do this every day when we decide whether or not to walk under a ladder or cross the road in a particular place.
We need to know just how unlikely it is to be killed by a tree.
The presumption should be one of retaining the tree, rather than reaching for the chainsaw at first sight of a "problem". There are ways of reducing risk other than felling.
In a park, it can sometimes be as simple as closing a path, or changing the mowing regime to make it less attractive for people to spend time under the tree.
Instead of reducing the risk by removing the tree, one could remove the bench under the tree. Having fewer people under the tree decreases the risk of injury. Or, one could give the canopy a trim.
"Fell and replace" is usually the wrong approach, as it will not provide us with the canopy we desperately need right now.
Then, we need councils to open up and consult before removing trees and also to develop strategies for increasing our urban canopies.
When trees are identified with problems, there should be consultation about the options, with all the facts disclosed.
But more than facts, we need to give some weight to ethical values, because people care about trees. We wouldn't ignore values in any decision on a historic building, so neither should we on trees.
Councils need to be up-front about the cost implications of different options. In Bristol, the tentative first steps towards consultation have just started with the first meeting this March of a Street Tree Forum.
Highways work should also retain trees rather than remove them.
Finally, it needs to become socially unacceptable for householders or insurance companies to petition for the removal of trees when the problem is the lack of proper foundations in our Victorian housing stock.
People who live in tree-lined streets should enjoy the benefits or move out.
Unless something changes fast, we will continue to lose our urban canopy at just the time that we need it most. Now that is a real risk.
Vassili Papastavrou is a biologist who works for the International Fund for Animal Welfare (Ifaw). He is particularly interested in large, long-lived organisms such as whales and trees
The Green Room is a series of opinion articles on environmental topics running weekly on the BBC News website
