Why we should plant more urban trees

'In towns and cities, every big tree counts,” says the landscape architect Brita von Schoenaich. “But land is now so valuable, especially in London, that it has become very hard to get them into any new development. At one planning meeting I attended, the tree officer from the local council asked if the size of the building could be reduced to accommodate one, and the room just exploded in laughter.”

The start of National Tree Week, is a good moment to consider the trees of our urban landscape. And the fact that it is the larger trees that we need most. All city trees add beauty and connect you to the natural world, but it is only the monsters that can soften the lines of big buildings and expanses of paving, and significantly improve air quality, soak up rainwater and combat heat.

Size comes with age, and it is mainly thanks to the Victorians that the streets and squares in our towns and cities are endowed with the hefty specimens we see today.

Therein lies another problem, says von Schoenaich. “Many of these trees are now so old that they are approaching the end of their healthy lifespan.” Central London is looking particularly vulnerable, since most of its mature leaf canopy comes from a single type of tree, the hybrid London plane, a tree that may soon be confronted with the lethal fungal disease stain canker, which is now on the march from southern Europe.

Finding a site for any new tree in an urban landscape is seldom easy. It is not just the space required overhead, but also underground. Our streets are now a maze of service pipes and cables which often puts the engineers and tree people in mortal combat – “trench warfare” von Schoenaich calls it.

Much of this ground is also compacted and airless. Once planted, with the ground improved, the tree roots directed and services protected, there is the matter of keeping the tree alive. About 50 per cent of urban trees don’t make it to 10 years old, whether through poor planting, aftercare, damage or change in land use.

Insurance companies also hover over trees like a spectre, though the danger tree roots pose to buildings is usually more imagined than real. Happily, insurance companies have now agreed a protocol with local authorities, accepting that cities do need trees and that even when trees are implicated in subsidence, remedial pruning rather than complete removal can be an option.

But sites can be found for trees, even in well-established tarmac land.

One inspiring example is in north London where, in an initiative by Barnet’s tree officer, Andy Tipping, an avenue of no less than 90 dawn redwood trees has recently been installed along a previously bleak stretch of the busy Edgware Road. It is one of 40 potential tree-planting sites Tipping identified. Setting himself up in the local library with display boards, he engaged with scores of residents and local business people, who responded to the idea of money being spent to beautify their part of the borough in this way.

This is the greatest asset trees have: most people like them. As he says: “You don’t invite the mayor to a tree-felling ceremony.” Getting the public involved from the start, including through schools, and keeping people engaged by caring for the trees well and promoting them as part of the town or city’s heritage also give the trees the best hope of reaching a ripe old age.

In an imaginative programme run by the London Borough of Hackney, residents themselves are invited to take the initiative, become Tree Champions and instigate tree planting in their own streets by canvassing their neighbours and asking who does or doesn’t want a tree outside their house. “We involve people in the selection of species too, and after planting, volunteers are appointed as tree carers and given a watering can,” tree officer Tom Campbell tells me.

In recent years, Hackney’s streets have become quite an arboretum – I like the fact that members of the Turkish community voted to plant almonds, a tree with a long cultural and emotional connection with Turkey – with very few trees dying or damaged. “It is remarkable how much better tree growth is on those adopted streets,” says Campbell.

Sadly, the money for such tree planting schemes in London, which became available via the Mayor’s Street Tree Initiative, has now dried up. And, of course, in an era of belt-tightening by local authorities up and down the country, finding the funds for serious tree planting (and aftercare) is going to be a challenge.

When it comes to trees in new developments, Brita von Schoenaich thinks there should be much clearer direction from local authorities.

“Cambridge is a good example of a city that gives firm design guidance on the inclusion of trees at the start of every project,” she says. “But in most other cities, trees are usually an afterthought in my experience. The local tree officer is involved only at a very late stage, by which time the design is decided and the space allocated. And without strong political backing, no one has enough power to get anything changed. So, instead of big trees, you end up with small or narrowly fastigiate varieties with little lasting impact on the landscape.”

The best chance of getting more big trees into the city, says Anne Jaluzot, a planning consultant with the advisory Tree and Design Action Group, is to put them to work as part of the urban infrastructure. “There is very little money allocated to the environment, but huge money allocated to services, so the key is to make trees part of how the city functions,” she says.

As an example she cites Lyon in her native France. “Trees are fantastic evaporation machines, and in Lyon they have been used to create a giant air-conditioning system.” In the formerly grim rue Garibaldi, a traffic underpass has been converted into a huge storage tank to capture rainwater, which is then used to give summer water to the avenues of trees above. “The trees don’t need watering to survive, but giving them this water keeps them evaporating, and so cooling the city through the hottest months.” The environment has become healthier and more attractive, with the trees also enticing more people to get on their bicycles and use the cycle lanes that run between them.

It was spending time in Chicago on an internship that alerted Jaluzot to the potential of using natural systems to deliver a better city environment. Chicago is a flagship of green, sustainable planning with an impressive tree-planting programme that has produced an “urban forest” of some 3.5 million trees. “These are put to work not only capturing air pollutants (the city’s website estimates that every year the trees remove some 888 tons of pollution and absorb 25,200 tons of carbon dioxide) but also its rain and stormwater.”

Now, instead of being channelled into the sewer system and being expensively treated, or running off to create a flood danger, much of this water is used where it falls by trees and in green spaces (including on the city’s 350 green roof gardens which capture 70 million gallons of stormwater annually), or else is stored for summer use or simply allowed to filter away and replenish the water table through permeable pavements.

In Scandinavia, Jaluzot tells me, the recycling process sometimes begins even before the trees are planted, with the ground prepared not with topsoil but stony waste from construction sites and harvested green waste (notably biochar, a charcoal produced from the oxygen-free burning of organic material, which both absorbs and purifies run-off water).

Recently, there has been a great step forward in encouraging towns and cities to think of their trees more than as decorative green icing. This is the i‑Tree software, developed by the United States Forest Service. After conducting a survey of the trees in their locality – how many, what species, how big – a local authority can use this software to calculate the economic value they bring in terms of services such as pollution removal, carbon storage and water absorption. Chicago, for instance, values its trees’ pollution removal service at $6.4 million (£4.23 million) annually and the overall structural value of its urban forest at $2.3 billion (£1.5 billion).

I was flabbergasted to learn from Anne Jaluzot that one of the first towns to use this software in the UK is none other than my local Welsh border town of Wrexham. Flabbergasted because greenery has never seemed high on the agenda as successive councils have remodelled the town. Nor indeed has visual beauty of any kind – remembering Wrexham’s lost green spaces and quirky market-town character sometimes brings real tears to my eyes.

“Trees have moved up the agenda!” Elton Watson, the town’s senior tree officer, assures me. “There is a lot of enthusiasm for them among our elected members now, and from the public.” Earlier this year, Wrexham won a gold award from the Royal Forestry Society for its creation of a three-hectare urban woodland and it is hoped that the council will soon approve a new tree strategy.

“i-Tree has shown us that we currently have 17 per cent tree canopy cover, producing environmental benefits equivalent to £1.2 million a year,” says Watson. “The goal is to go to 20 per cent, with our tree strategy informing planning guidelines for all new development.”

I hope homes will be found for trees in the town’s older developments too – a big tree can hide a multitude of architectural sins. But I am excited, and if Wrexham is getting fired up by trees, maybe nationwide we are at last starting to embark on a legacy to match that of the Victorians.