Gardening: Don't be afraid to go out on a limb: Does your hazel need a haircut? Anna Pavord recommends a trimming technique that can add great character to your trees

TREES are much on my mind at the moment, engaged as I am in fisticuffs with the local electricity board. 'It is a requirement of the Electricity Act (1989),' they write, 'that safe distances are maintained between overhead electric lines and trees to avoid unauthorised access and prevent accidents.' That, of course, is entirely reasonable.

The battle concerns their interpretation of a safe distance. 'Minimum clearances to be maintained are 3.0 metres to any branch capable of supporting a ladder or climber.' Their tree maintenance is carried out on a four-year rota. That 12 feet, they reckon, is the minimum necessary to protect the lines until 1997.

But the trees in question are a yew and a bay. The bay (Laurus nobilis) is an ancient tree with a trunk 3ft round. It moves more slowly than a teetotaller towards a gin bottle. At 24ft, it must be near its maximum height, as it has not shifted in the 18 years we have been in the house. Nor is the yew known as a sprinter.

Three metres may be a safe margin where you are dealing with elder and hazel, field maple and hawthorn. But it is sacrilege where a bay or yew is concerned. And unnecessary. Round three will be fought any day now, but I am not sure that my own fighting weight matches that of my opponent. The electricity board is confident that its demands override the tree preservation orders which the wise local council attached to all the best trees in the garden before we ever arrived.

One of the orders concerns an ancient pollarded ash (fortunately, far away from anything that affects the electricity board). The trunk measures about 7ft round and the pollarding started about 5ft from the ground.

Pollarding was used as a way of harvesting timber regularly from a tree without Chopping it down. Instead of allowing the tree to grow unchecked, you cut out branches in rotation from the crown. As the tree ages, it acquires great character, the trunk swelling and the regrowth from the pollarded branches all sprouting together from the same point.

Our tree was probably pollarded for firewood, since ash provides some of the best logs for burning. In old woodlands, such as Hatfield Forest in Hertfordshire, trees were also pollarded to provide summer forage, especially for deer.

Now pollarding has come back into fashion, as it fits well into the philosophy of 'sustainable resources'. You milk the tree rather than slaughter it. The technique is also useful for reducing the size of a tree or regenerating new growth in one that is beginning to look moribund.

Our ash had probably not been pollarded for 100 years, judging by the size of the top growth. Each upright branch was itself a sizeable tree. Over the last 10 years, we have gradually been reducing this top hamper, taking out one large upright each year. The job was finished this winter. The tree quickly furnishes itself with a fuzz of new shoots, one or two of which will grow into proper branches. This gradual nibbling is less of a shock to the tree than wholesale decapitation, though not as convenient if you have to hire in tree surgeons to do the job.

Pollarding was reintroduced in the Hatfield Forest in the late Seventies, and experience there has shown that the little by little approach is by far the most successful. At the beginning of the programme, six old oaks were given total pollard haircuts and only one survived. Since then the foresters have changed their technique. Eight kinds of tree seem to have been pollarded at Hatfield in the past: oak, hornbeam, ash, field maple, beech, elm, hawthorn and crab apple.

The best time to cut seems to be in February and early March. This is possibly because the new buds that form to replace the lost branches are at risk for the shortest possible time to frost damage. It may be that water tables are generally at their highest at this time and the tree has no problem gathering resources for a more than usually demanding spurt of growth.

Judging from our ash, new shoots tend to break a little way below the place where the branch has been cut off. To give the tree the maximum room for manoeuvre, it is probably best to leave about a foot of stump and encourage as much new growth as possible.

Not all trees respond to the pollarding treatment. Holly would not. Nor, of course, would trees such as Leyland cypress, which do not have much in the way of proper branches. Willows, on the other hand, make classic pollards.

The technique could be used more on street trees, where size needed to be restricted. Too often they suffer ugly half- amputations, which have a very different effect. But the kinds of trees that are planted are not often the kind which would lend themselves to pollarding.

A little while ago the Forestry Commission carried out a survey of 3,600 street trees. Just five kinds, acer, sorbus, cherry, birch and lime accounted for 70 per cent of all the trees they saw. That is surprising and rather depressing. We would all benefit from a richer, more varied diet. The trees would gain, too, as epidemics, which tend to focus on particular kinds of tree, would spread less quickly.

Vandals are commonly supposed to be the biggest hazard to street trees. The survey found otherwise. Deliberately inflicted damage affected 1.5 per cent of them. Accidental damage was far more of a problem, affecting 15 per cent of all plantings. Some trees had been sabotaged by strimmers and mowers used by contractors who must have been working with their eyes shut. Some had been poisoned by overdoses of herbicide. Some had been strangled by stakes and ties that nobody thought to loosen as the tree increased in size. Take some time off from worrying about the rainforest to worry about the tree outside your front gate.

So far, it has been a relatively good winter for trees. There has been plenty of rain to replenish the sinking supply. Although there have been gales, in most parts of the country they have not been as ferocious as those of 1987 and 1990. Temperatures have generally been mild, which means less salt on the roads.

Trees hate salt, and roadside trees can suffer badly from its effects as it sinks down through the soil to their roots. Buds fail to open or die back as soon as they have. Leaves turn brown and drop. Large sections of the tree may die back.

The problem with salt is that it is too easy to overdose. An extra shovelful for luck is anything but lucky for the tree on whose patch it lands. There are alternatives to salt. They are expensive, though not so expensive as replacing a dead tree.

There is still time to plant bare root trees, which I favour over container-grown specimens. Roots are too often cramped in containers and cannot provide sufficient anchors for the tree when it is planted out. If it must be container grown, pull the tree out of its container to check the roots before you buy. Reject any with roots coiled like snakes in a basket. Trees that have been grown in a loam-based compost will transplant to the open ground more easily than those grown in looser peat composts. Resist the temptation to go for instant effect; small trees settle much more easily than big ones.

Some are much more tolerant of air pollution than others. If this is your problem, look for alder, hornbeam, the Indian bean tree (Catalpa bignonioides), the Turkish hazel (Corylus colurna), hawthorn, the maidenhair tree (Ginkgo biloba), holly, crab apple, pear and robinia.

For details of fully qualified tree surgeons, contact the Arboricultural Association (0794 68717). For information about the Tree Warden Scheme, a national initiative to encourage people to look after their local trees, contact the Tree Council, 35 Belgrave Square, London SW1X 8QN (071-235 8854).

(Photograph omitted)