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Trees Promote Health and Climate Mitigation

By Isabella Kaminski, The Developer

Governments love a good tree-planting scheme, because they’re popular and always hit the headlines. The latest source of funding, announced by former environment secretary Michael Gove in May, is a £10m pot available to councils, charities and individuals to plant 130,000 trees in towns and cities across England.

The money is certainly welcome. The UK has just 13% overall woodland cover – very low compared with most other European countries – and has made little progress in increasing it in recent years. The latest figures from Forest Research show only 1,420 hectares were planted in England in the year to March 2019, against the government’s 5,000-hectare target, with smaller areas in Wales and Northern Ireland. Only Scotland met its goal, planting about 11,200 hectares last year.

But critics point out that, while 130,000 trees might sound a lot, it is only a drop in the metaphorical ocean. According to a recent Committee on Climate Change report, which emphasises the crucial role trees play in tackling climate change by storing carbon, we should be planting 30,000 hectares of woodland each year – equivalent to around 1.5 billion trees by 2050.

Sharon Hosegood, chartered arboriculturist and consultant, says £10m is a good start “but it’s obviously not enough. [There] needs to be a collaborative approach by the government, local government, developers and private individuals to pull together because we desperately need more trees”.

Dan Raven-Ellison, who has campaigned to make London a National Park City, says the capital already has nearly as many trees as people, covering 21 percent of its area, but would like to see many more.

Trees have multiple benefits. Many of these can be quantified through a tool called a tool called i-Tree, which gives a detailed picture of the value of green infrastructure in cities such as London and Manchester.

trees and climate change solution

As well as storing carbon, trees help counter the ‘urban heat island’ effect, whereby cities are warmer than rural areas. Wide-canopied trees provide physical shade and cooling in summer and warming in winter, which reduces the amount of energy needed for heating and air conditioning. This effect is more pronounced during heatwaves as the climate warms.

They also demonstrably improve air quality; large-leaved species in particular help reduce fine particulate pollution (PM2.5). They boost biodiversity by providing homes for wildlife, reduce the risk of flooding by slowing down surface water runoff and improve soil health.

There is growing evidence that trees and other green spaces improve people’s physical and mental health; a recent study found that a two-hour ‘dose’ of nature once a week significantly boosts well-being. And while money doesn’t grow on trees they do have measurable economic benefits, boosting local house prices and encouraging trade by sprucing the area up.

“They calm us down, they clean the air, they make us money,” summarises Hosegood. And mature trees do all these things better.

Hosegood says developers and councils are increasingly recognising these benefits. “In my work for a London local authority housing department there’s a really good tree population and the landscaping has been greatly enhanced as part of privately funded development.”

While money doesn’t grow on trees they do have measurable economic benefits, boosting local house prices

Part of the battle to increase the number of city trees is not to cut existing ones down. There are already significant barriers in place to doing this, with many trees protected by Tree Preservation Orders or within wider conservation areas.

Developers are restricted in what they can fell. Part of Hosegood’s job involves assessing the state of existing trees on a development site, which is a statutory part of most planning applications. She looks at “how big they are, how healthy they are and what their role is in the landscape”, in line with British Standard (BS) 5837.

“It’s much better to get in early, preferably before the developer has bought the land, so we can work with the team – architects, landscape architects and engineers – to create a design that retains the best trees on site,” says Hosegood. “There’s always going to be some tree loss – that’s inevitable – but if we can have a design that tries to keep the best trees and can mitigate the tree loss, that’s really important.”

Greater Manchester’s City of Trees project has already planted half a million trees

Planting new trees is a whole different challenge and everyone agrees that there is no single correct way to do it. Greater Manchester’s City of Trees project, which aims to grow the local tree population by at least three million within the next generation, has already planted half a million trees in a variety of locations; from large plots of urban woodland on the city’s outskirts to pocket parks tucked between housing estates, to trees sprouting out of pavements.

Each type of planting has its own advantages and challenges. Parkland or woodland settings require considerably more land but once planted provide a more naturalistic landscape and may need less maintenance. Hard city landscapes also hugely benefit from greening, says Sarah Nurton, marketing and communications manager at City of Trees, but are particularly difficult to plant in.

Councils, highways organisations and nearby shopkeepers may need to be consulted about street trees, pavements must be wide enough to accommodate both the tree and passing foot traffic (including wheelchairs and buggies), and parking and entranceways cannot be obstructed. Meanwhile, some councils are concerned about insurance claims from subsidence caused by tree roots. “It is quite an expensive, time-consuming process and that’s before you even get to digging up pavements and getting a tree in,” says Nurton.

An important decision that developers and others must make is which species to plant. The Trees and Design Action Group (TDAG) produces a helpful free guide on this which is available online.

While there has been a move back towards native broadleaf trees such as oak in rural woodland, experts say these are not necessarily the best option in cities. Some woodland trees simply cannot be planted in urban locations. David Elliott, chief executive of tree planting charity Trees for Cities, says beech trees, for example, have very shallow roots that extend outwards, making them unsuitable for hard landscapes.

Meanwhile many native species are currently affected by serious pests and diseases, such as oak processionary moth and ash dieback disease. “The pool of our native species, which isn’t that big anyway, is drastically reduced,” says Elliott. “In order for trees to thrive and do well, to be healthy and resilient, the industry believes that you need to have a wide range of species.”

Hosegood stresses that large-canopied trees are still important to maximise shade. “There was a tendency until recently for landscaping schemes to use smaller species trees with a smaller canopy because it was deemed safer and wouldn’t give any trouble. There were fewer maintenance problems and it was cheaper. But there’s been a lot of lost opportunities. We need large trees where the space allows – things like London plane – but actually we need to be looking beyond our normal native trees because of climate change.”

Changing climatic conditions means cities are becoming wetter during some parts of the year and drier and hotter at others. Nurton says City of Trees is considering which trees will survive the next 50 years and notes that some species are already being planted that would not have survived several decades ago. Paulownia – also known as the foxglove tree – is native to central and western China and can be killed by harsh winters but has thrived on St Peter’s Square in Manchester city centre. “It’s about making our trees and woods more resilient for the future,” says Nurton.

Another important consideration is what to plant trees in, because cities are bursting with buried infrastructure such as telecommunications cables, gas and water pipes and old building foundations.

“Developers need to think not just about the above-ground space but invest money in the below-ground space,” says Hosegood. “What we’ve found in the past is that trees are sometimes just plonked in a hand-dug pit in the ground and left to get on with it. In a rural area that’s absolutely fine. But in cities we have such competition for space underneath the ground [that] specialist tree pits are incredibly important.”

A number of specialist suppliers sell modular systems that allow roots to flourish beneath hard surfaces and can maximise the water retention benefits of tree planting.

Julian Tollast, head of masterplanning and design at property development firm Quintain, which has won awards for its tree design at Wembley Park, says specialised technology is expensive but helps trees thrive, especially in the early years. Although Quintain generally favours watering trees manually with a hosepipe because “you know exactly what has been delivered”, it has installed automatic irrigation systems underground in some areas.

Hosegood adds that, where possible, developers could plant several trees in one big pit rather than individually.

“You have a bigger soil volume for all the trees to exploit together. It’s much better for surface water attenuation. It has a better visual impact and it’s better ecologically as well because it’s a more viable habitat for creepy crawlies etc. It seems like a cost… but I say it’s really important because it’ll make their development really shine when people go back.”

Then there is the matter of long-term care. Hosegood says it is helpful when planning permission includes maintenance conditions specifying how trees are to be looked after for a fixed period, often five years. This is usually done by a maintenance company, contracted by the council or the developer itself.

At Wembley Park, however, Quintain remains responsible for the site. “We took a long-term stewardship of the landscape we’re creating,” says Tollast, “which really helps because I can chat to my colleague, learn from the last area of landscape we did on the challenges or otherwise we’ve had of maintaining that and make sure we put those lessons learned back into the next phase of the project.”

The new requirement for developers in England to show that projects have a ‘net gain’ for biodiversity will encourage more tree planting.

Trees for Cities looks after its new street trees for three years after they are handed over to the landowner – usually the local authority. Elliott says most trees aged between three and 20 years do not require a lot of work. “Then when they’re bigger you start to need to do pruning or pollarding or take them down if they’re starting to die off,” he says.

Progressive developers are even involving the public in the installation and long-term care of their trees. Elliott of Trees for Cities, which relies on a mostly voluntary workforce to create its urban woodlands, community orchards, leafy parks and street greenery, says local communities that plant trees “will take more ownership and care for them”.

Hosegood says getting communities involved is also “an opportunity for developers to show they’re different from their competitors and to show their green credentials”. Having children plant trees on a construction site is “tremendous education and it’s great for PR”, while making community groups responsible for longer-term management of nearby woodland is “a mechanism for the new people who are moving in to get to know each other.”

It is also important because trees can be an emotive subject. Protests erupted in Sheffield in 2016 when contractor Amey started felling street trees as part of a 25-year private finance initiative contract with the city council.

For Elliott, a good tree-planting project is one that maximizes its benefits, so he welcomes the fact that the Urban Tree Challenge Fund prioritises social factors as well as environmental ones.

Nurton, who often works with social housing providers, says they are particularly enthusiastic about the idea of greening patches of land that might have attracted anti-social behaviour. “If we can bring that woodland back into use for the community, we might twin it with a local school. They use it as an outdoor classroom so it’s much less likely to get fly-tipped and people see it as an asset rather than an eyesore. They really see the value of that.”

Elliott thinks there is still a lack of consistency in how green infrastructure is approached in different areas and says it is not completely embedded in the wider planning and development sector. “But there is a rapidly increasing [realisation] of the value of green in urban development. It is being taken much more seriously.”

He hopes that a new requirement for developers in England to show that projects have a positive impact or ‘net gain’ for biodiversity will improve things further.

Nurton agrees. “When it comes to costs… it can be hard to prioritise green space and trees within developments, which we completely understand. But I think it’s becoming more and more integral now for developers to ensure that it’s one of the strands.

“It’s not just about building flats; it’s about creating environments people want to be in.”

Greener Cities and climate action

Greener Cities is a division of Crossbow Communications. Greener Cities is a resource for sustainable and resilient cities and communities around the world.

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Author: Gary Chandler

Gary Chandler is a sustainability strategist, author and advocate. Follow him on Twitter @Gary_Chandler