Network: Software that saves London's trees: David Nicholson-Lord finds there is more to urban forestry than lopping off branches

IT'S MORE exciting than you might think, being a council arboricultural manager. Scarcely have I begun to talk to Paul Akers in his cramped office in Westminster City Hall when the telephone rings with news of an emergency near Downing Street. Emergency] Downing Street] The line crackles urgently: police are being called, a roadblock is needed.

Crikey] Could it involve, you know, a person called John?

Indeed it could. John, one of Paul's assistant tree men, is off with his mobile phone, and within minutes rings in. A lorry has hit a plane tree in Whitehall, there's wood everywhere, a 'sodding great limb' is blocking the road and the police want action.

Paul rings Pete, of 'G and Ts' (Gristwood and Toms, tree contractors), and Pete says he will be there within the hour to rope off, trim and lop. Paul passes this on to John, on the mobile, and John tells the police. They don't teach you all that at forestry college.

'We're on 24-hour call here,' says Paul, grimly. 'Well, I am anyway.'

If the police had wanted it, John and Paul could have supplied them with a detailed biography of the tree covering 30 features, from height and girth to when it was planted and how far it is from buildings.

Westminster operates one of the first computerised inventories of the trees under its control - a 'multi-relational database' covering street, park and housing estate trees, which can tell you at the touch of a button whether a plane tree in, say, Mayfair has a history of insurance claims for subsidence, or how many trees in the borough may be banging into buses.

Actually, we know that particular figure - about 300.

Trees are often unfairly blamed, and destroyed, for causing subsidence. In fact, one of their chief aims in life is to escape buildings, in pursuit of light. In central London, this often means they grow over the street.

Several had to be chopped down in Charing Cross Road recently because they were leaning across the road.

The computer also helped to prevent an epidemic of brown-tail moth attacks on cherry and plum trees across London. When the council discovered evidence of the destruction wrought by the moths, they were able to pinpoint the hundreds of other trees around Westminster that would need to be sprayed with protective chemicals.

Perhaps surprisingly, since a desktop computer would easily have been able to store the data, the tree software runs from the council's main system. It was necessary to link the tree database with the software used to process planning applications to be able to alert the council if a new building would harm a tree subject to a preservation order.

The link means that other Westminster workers can look at the database from computers already installed.

Who needs a multi-relational database? Paul Akers gestures towards shelves groaning under a weight of as-yet uncomputerised contract files. But the computer is more than a space-saver, or even a management tool - enabling, for instance, a three-year pruning cycle to be established instead of the old 'fire-fighting' regime, which often involved leaving trees uncut until somebody complained. It also provides quick answers for an increasingly tree-conscious public.

He believes the storms of 1987 and 1990 helped to focus attitudes. 'They rang a lot of alarm bells - people woke up the following morning and could not adjust themselves to what had happened. The storms did a lot of harm, but they also did some good - trees are considered much more than they used to be. But because of the greater interest, our workload has increased. We have got to respond quickly.'

As if in illustration, an urgent message arrives from the council leader's office. A man has telephoned from Belgravia 'almost in tears' at the impending execution of a tree that was subject to a preservation order but said to be damaging a building. The leader is contemplating a stay of execution, but needs briefing. In this case, human memory assists the computer. 'The tree was about this far from the house,' recalls Mr Akers, holding his hands six inches apart.

The database owes its origins to a survey of Westminster's trees in the early Eighties funded by the Manpower Services Commission. It showed that there were fewer trees than planners had thought. Today, after several years of planting, there are about 6,700 street trees, compared with the pre- computer 'guesstimate' of 10,000 (there are another 2,660 in parks and 5,000 on housing estates). However, London planes were far more dominant than previously suspected.

Hence, in part, the decision to diversify towards smaller, less long-lived species. These do not disrupt buildings or need regular maintenance; but they supply the generalised sense of greenery that, according to Mr Akers, is all many people want from the urban tree. Hence the spread of the chanticleer pear along Oxford Street.

The computer tells him that Westminster's tree stock is increasing at the rate of 250 a year, that the survival rate of trees planted is a remarkable 95 per cent - but that the city is running out of space for more street trees.

Much of central London conceals, six inches below pavement level, old coal and log storage vaults. These are usually an obstacle to planting, but in leafless areas they can, if they are unused, be turned into 'tree pits'.

As for the 5 per cent of trees that don't survive, they are often the victims of traffic: the Downing Street emergency was typical. But since the pounds 425,000 spent on trees each year is financed from parking meter charges, perhaps we shouldn't be too quick to blame the motorist.

(Photograph omitted)