Science: The assault course for urban trees: Landscapers will stump up pounds 10 each for saplings, when seedlings at 20p a time would have a better chance of survival, says Patrick Matthews

IT IS a sad example of inner-city vandalism, but someone in my north London suburb has been trying to kill off trees as fast as my local council can plant them. At the last count about 70 had been expertly attacked with a Stanley knife. Fortunately, he (if it is a he) has not been too successful, for most have survived.

At a nearby housing estate, which the council landscaped last winter, only a small proportion of the saplings are still alive. Almost certainly they died because of the handling they received from the nurserymen or the contractors. The young birches were victims of what a member of the Forestry Authority (since April 1992 the regulatory half of the Forestry Commission) sorrowfully termed 'municipal vandalism'.

Britain's trees are in poor health generally, but few are in as rotten shape as those scratching a living in the inner cities. A study by a team from the School of Landscape Architecture at Heriot-Watt University, Edinburgh, reported that 46 per cent of trees planted in Edinburgh and Glasgow in 1979 died within five years.

In the course of his job, Simon Hodge, the Forestry Authority's project leader on urban trees, has come to firm and sometimes unwelcome conclusions about the reasons. He blames not pollution nor vandalism, but wilful neglect: the necessary conditions for survival have simply not been met.

Mr Hodge has made a detailed survey throughout Britain. In towns, he found that most healthy trees were older trees, simply because so many recently planted young trees fail to survive their first few years.

So what exactly was it that caused the decline of the young birches in my neighbourhood? Mr Hodge claimed the odds had been stacked against them. 'It's one of the worst species to choose. Birch is fascinating: the seed will blow in and grow on unpromising sites, yet it's particularly difficult to establish as a young tree.'

Even so, he thought that casualties could have been kept to a minimum. The roots should have been protected from drying out at all costs. Afterwards the secret is plenty of watering. But the provision of maintenance funds for this kind of after-care is rare - even though local authorities often sweep any unused capital funds at the end of a financial year into 'environmental improvements'.

The saplings were also handicapped by being fully eight feet high when planted - smaller trees, said Mr Hodge, would have fared better. 'The important thing is that the bit above the ground gets supplied with what it needs from below the ground. When a big tree is lifted by the nursery, 90 per cent of its root system is left behind.' Instead of planting well-grown trees, at a cost of at least pounds 10 each, seedlings could be planted for just 20p each. These would have every chance of outgrowing their stricken seniors.

The researchers at Heriot-Watt agree that size offers no advantage. In a follow-up to their first Scottish survey they looked at 520 trees planted for the Glasgow Garden Festival in 1988. Expense had been no object: these semi-mature specimens had cost no less than pounds 200 apiece. Yet in 1990 only 53 per cent were in an acceptable condition and just 8 per cent classed as in good condition.

'We found that the soil had been very poor,' said Catherine Mitchem, a research assistant at Heriot-Watt. 'Losses were also due to the way the trees were treated at the time of planting - for instance, allowing the roots to dry out.'

Expense apart, a tiny plant has the advantage of offering little provocation to a vandal with a grudge - in contrast to the north London housing estate where dead birches cluster in newly made shrubberies as part of a big landscaping project. As Mr Hodge put it: 'A scheme like this one oozes a sense of 'the authorities'.'

No one knows exactly why people wreck trees. There would probably not be enough convicted vandals to interview for a systematic investigation. Talking to residents around the country, Mr Hodge's main finding is that people are ambivalent to new planting. They see a balance of advantages and disadvantages. On the debit side are the mess from leaves, berries and aphids, the casting of unwelcome shade, pavements cracking, and fears of damage to the house or the car in a gale. The answer is to plant only where it will cause the least inconvenience, and, where possible, to start from small beginnings.

'Big trees on high-impact schemes have a very high 'challenge value'. Vandals have the satisfaction of knowing they cost a lot of money. Smaller ones can get established without offering a challenge. In the Black Country I've established woodlands of several thousand trees and lost only half a dozen. People just don't bother.' But the battle can be lost even with the residents' goodwill and a wise choice of species. Much urban soil, Mr Hodge believes, is simply not good enough. His prescription is to test for nutrients and, where they are missing, dig out and replace at least two and a half cubic metres of soil, preferably over a wide and shallow area.

'If the rooting conditions aren't good, trees remain unstable. A lot of casualties from the 1987 storm were the result of a poor root system. The other big problem is that if you don't take care, they can grow very shallowly and begin heaving up the area around them. A good environment can direct the roots away from pipes and paving stones.'

This recommendation can be irksome to local authorities. 'I think he's talking out of the back of his neck,' snorted one council tree officer. 'We can't go digging up half the road and half the pavement.'

In that case, Mr Hodge retorted, concentrate your efforts elsewhere. In London, streets have been designed to include trees for only about the past hundred years. London plane trees originally belonged in Georgian squares, not on pavements. Older streets tend to have little room for spreading roots, and any topsoil that might have nourished at one time, has usually long vanished.

The new fashion started in the Seventies when cleaner air first made it possible to put in a wide range of species. Planting was now not just intended to look attractive, but aimed to soak up pollution and encourage wildlife. And despite the high rate of attrition, there have been many successes - even, as Mr Hodge and his fellow researchers would see it, against the odds.

'People are very used to handling bricks and fences,' says Ms Mitchem. 'It's difficult for them to remember that trees are living things. So much work has been done on how they establish; it just isn't being put into practice.'

According to Mr Hodge, the whole art of tree planting can be reduced to understanding three things: the needs of the site, the biology of the tree and the wishes of local people.

'There might be all sorts of good reasons why it seems necessary to compromise. Some money might suddenly come through in March so the tree officer has to take any stock left at the nursery, whatever condition it's in. There might be political reasons to for making a quick impact. But you can't explain that to the tree. The tree either lives or dies.'

(Photograph omitted)