Are our urban trees in danger?

As a child growing up in the suburbs of London during the Sixties and Seventies I walked to school. All my classmates did the same. Today, 40 years on, if I close my eyes I can trace every step of that 20-minute journey in my mind as if it were yesterday. Apparently this is not unusual, according to the Living Streets campaign (livingstreets.org.uk), the walk to school is one of those childhood memories that stays with us until we die.

My route took me past red-brick Coronation Street terraces, pebble-dashed semis, high street shop fronts and the railings of the local park. For close on half of that journey I walked beneath a canopy of street trees. The rest of the time the house sparrows called from the boughs of neighbouring gardens and parks. At that time I knew very little of the countryside, nor that my future career would somehow involve plants, but I did know those trees, as did all my mates. As Britain celebrates National Tree Week, which starts today, it is a good moment to ask whether today’s schoolchildren will have the same leafy memories.

We knew it was the horse chestnut we thrashed at with sticks to release its shiny brown conkers, and we knew the winged seeds that spun through the air like helicopters came from sycamore. We knew it was lime that spread sticky black goo on the kerb stones and cars, we knew the best trees for climbing were the heavy-branched London planes, the bark of which flaked off beneath our Clark’s shoes and we knew it was elm, normally sulphur yellow in autumn, that was filling the gutters and drains with deformed twigs and blackened dead leaves.

I saw my first ever chainsaw in Elm Grove. We scooped up the sawdust, which the roaring machine spewed out across the pavement, and threw it around like confetti. We laughed and danced at the noise and the fumes – little did we know that this was the start of a series of events that would change our landscape forever.

By 1976 all the elm had gone and the bubbling tarmac stuck to my soles all summer long. That drought saw off whole avenues of limes and those that lived on, defiant but with shrivelled roots, finally toppled on October 16 1987, as did the plane trees all over London. On the night of the Great Storm more than 15 million trees blew down across southern England, three million of them in city streets and parks like mine.

_{Leaves aplenty: Ginkgo bilobaand Metasequoia glyptostroboides weren’t around in the Thirties (GETTY)}

With 19 people dead, three million houses damaged and the insurance industry having to pay out almost £2 billion, it was understandable that in some quarters there was a degree of wariness and reluctance to simply replace what had just blown down. Nevertheless, within days of the storm, the Government had asked the Countryside Commission (now Natural England) to set up a task force to “initiate appropriate action, create an awareness of the importance of trees in our towns and countryside and to set the pace for an ambitious restoration programme”. In April 1990 Margaret Thatcher planted the millionth tree of the restoration programme, a Himalayan birch, in Victoria Embankment Gardens, not far from 10 Downing Street, and said she was “looking forward to another million trees being planted”.

In fact, by the time of her death in April this year, it was estimated that in excess of 500 million trees had been planted in the UK since the Great Storm – not just through the task force, but collectively through government funding and private initiative – bringing Britain’s tree cover back up to around 12 per cent, roughly equal to what it was during the Victorian era.

However, any similarity with Victorian Britain ends there. While the Victorians populated our town and city streets with London plane, horse chestnut, sycamore, common lime and English elm (the trees I had walked beneath on my way to school), post-1987 city tree planting has been very different.

Margaret Thatcher’s Himalayan birch (Betula utilis var. jacquemontii) set the tone, for this is a tree of the modern age and one that was not even discovered and introduced into Britain until the Victorian era was nearing its close. Today’s urban environment is populated by a diverse and eclectic mix of trees from all around the world, not just that part painted pink on fading colonial maps. Take a walk, for example, along the streets from Westminster in the direction of Chelsea and you will find dawn redwood (Metasequoia glyptostroboides) from China, evergreen oak (Quercus ilex) from the Mediterranean, flowering ash (Fraxinus ornus) from south-west Asia, cherry trees from Japan, magnolias from the United States, maples from Canada and strawberry trees from Greece.

_{Mayor Boris Johnson helps replace London’s ageing plane trees (GETTY)}

In fact, in the London Borough of Kensington and Chelsea alone there are 162 different varieties of trees planted on the streets. While this level of diversity may not be repeated in every town across the UK, there is no doubt that the palette of species we can now choose from to plant in our streets, whether we live in Folkestone or Fife, is far wider than it has ever been.

Horticultural commerce has driven not only the search for new species from abroad but also the cultivation of new varieties from those species. It is big business and if you are the nurseryman who finds or cultivates a new variety of tree which produces scented flowers as big as a water-lily and it blooms for 200 days each year, you could become a multimillionaire almost overnight.

However, just because there are more trees to choose from does not necessarily mean that town and city councils are going to adopt them into their plans. Availability is only part of the criteria, just as important to local government officials is a tree’s suitability for urban use in the 21st century and it is here that we must return to our chronological list of disasters. For outside influences on what lives, grows and dies in our streets did not end with the 1987 storm, in fact they began to increase with a rapidity never seen before. By the Nineties we were being bombarded with information about the detrimental effects on trees from pollution, acid rain, excess carbon dioxide and holes in the ozone layer. In a matter of just a few years the term global warming was the new hot potato.

Computer models from climatologists suggested that native trees such as beech — itself a widely planted tree in urban parks and gardens — could die out by 2050 in south-east England, if predictions for a two to three degree increase in mean temperatures were correct.

Other urban trees, such as horse chestnut, would also become liable to branch-drop and root dieback in years of drought. Suggestions such as these had a profound effect on local government and other organisations responsible for tree planting in urban environments, for they indicated a ratcheting up of risks to both human health and safety and property and of course the litigation claims that would inevitably follow.

Not only that, with budgets being squeezed ever tighter and few councils awash with manpower, it became evident that trees which require a high degree of regular maintenance, such as pruning, limb removal and pollarding, simply could not be sustained. Included within that category were London plane, common lime and horse chestnut, all urban stalwarts from the Victorian era.

While there was a growing awareness that some of the urban trees we had relied on for the past century or more were no longer fit for purpose, there was also an understanding that planting more trees, both in urban and rural locations, was a key way to help offset the problems caused by global warming. However, deciding which trees should be planted was not easy and it was about to get even harder.

By the Millennium the phrase “global warming” was losing ground to “climate change,” as scientists began to understand that an increase in global temperature would affect our climate both on a global and a local scale – and this did not necessarily mean that UK summers would become uniformly hotter and drier. More likely would be the occurrence of extreme or freak weather conditions, which could just as easily flip from a run of wet summers, such as experienced from 2007 to 2012, to periods of drought. High winds, storms, flash floods, long periods of sub-zero temperatures, heavy falls of snow and shifts in the seasons were also more likely.

If that was not enough to make tree-planters scratch their heads, then the 2007 Forestry Commission report Trees and Climate Change most certainly was.

In this report it became clear that the kinds of trees we would need to rely on in the future would not only have to contend with freak weather conditions. They would also have to be able to fight off prolonged and successive assaults from a host of alien pests and diseases that would potentially be able to gain a foothold in Britain as our climate changed and global trade increased. The report went on to detail some of the likely threats. These included Phytophthora ramorum (known as sudden oak death), Cameraria ohridella (horse chestnut leaf minor) and Dothistroma (red band needle blight).

Six years on, all of these pests and diseases are now causing serious problems and have already resulted in the felling and death of thousands of British-grown trees. They have also been joined by a number of other tree killers, including Pseudomonas syringae pv. aesculi (horse chestnut bleeding canker) Cryphonectria parasitica (sweet chestnut blight) and Chalara fraxinea (ash dieback).

Over the past year it has been ash dieback that has captured the headlines and it took centre stage at this year’s RHS Chelsea Flower Show when it featured in the “Stop the Spread” garden, designed by Jo Thompson and sponsored by FERA (Food & Environmental Research Agency). From the garden (which included an avenue of dead trees), Owen Paterson, the Secretary of State for Environment, announced a series of recommendations from the Plant Health Task Force in an attempt to counter severe criticism that earlier government intervention could have prevented ash dieback from entering the country. Quite what kind of impact this disease will have on our landscape remains to be seen.

There is now an understanding that trees are useful, in fact essential, to our town and city streets, for a host of reasons: shade and shelter, pollution and flood control. But which trees should we be planting to ensure that future generations have at least a chance of walking to school beneath a leafy canopy? As the changes over the past half-century suggest, this is something of a moving target.

We are lucky to live in a country that loves its trees. So, to mark National Tree Week, take a moment to look at the trees on your route to work and ask yourself if you could do more to appreciate them – or be more vigilant about protecting them.

For more information about National Tree Week, and details of how to contact a tree warden in your area, call 020 7407 9992 or visit Tree Council