Trees, design and cities

Let’s start with the facts.

Trees are among the largest living things on earth. There are about 3 trillion of them, covering around a third of the planet’s land surface, drawn from a staggering 58,493 species. Brazil has the most native tree species in the world at 8,715; Britain has 60 or more, the majority of which are broadleaves.  

The oldest-known living specimen of bristlecone pine – aptly named ‘Methuselah’ – is 4,853 years old, and lives in the White Mountains of California. This tree germinated from seed in 2832 BCE during the middle period of the Bronze Age, as empires first emerged in Mesopotamia.

Their antiquity and diversity signals how important trees are to human existence. In his nature-writing classic The Ash and the Beech: The Drama of Woodland Change Richard Mabey puts it this way: ‘To be without trees would, in the most literal way, to be without roots.’ And while we instinctively know that trees matter, it’s worth reiterating the benefits.

Trees clean the air we breathe, absorbing carbon dioxide and emitting oxygen. They provide shelter and food, together with an immense range of products of inestimable value to individual livelihoods, national economies and global trade.

They are crucial to the environment around us. Forests support at least half of the earth’s terrestrial plant and animal species. Oak trees alone, for example, support 2,300 species – 326 of which are entirely dependent on oak for their survival.

Trees also have a profound effect on our wellbeing. The psychologist Carl Jung identified the tree as an archetype, a symbol hard-wired into the human consciousness. They stand for growth, life, protection, solidity and nourishment. If you really need to put a price on that, research suggests that woodland walks alone save the British National Health Service £185m a year in mental health costs.

All this illustrates the obvious point that trees should be a central priority for cities and for the people who design them, above all in a climate emergency.

So how do we get this right?  Here are four examples from the last ten years to bring the debate alive.

Stefano Boeri’s Vertical Forest in Milan is ‘a home for trees that also houses humans and birds.’ It consists of two residential towers for 480 residents, with 800 trees and 30,000 square metres of woodland and vegetation nestling within its terraces. The choice of trees was based on three years’ extensive research, and the saplings were grown in nurseries with similar conditions to their planned final positions.

64 varieties of tree and 94 varieties of plant provide a home for over 20 different bird species, not to mention countless butterflies and other insects. Irrigation, managed by a digital control system, uses mostly filtered waste water from the blocks. Maintenance of the trees is rigorous: there were six checks in the first year after completion and now four annually, one of which is by ‘flying arborists’ who abseil down the outside of the towers.

While this was being built, A Thousand Trees, a project by Manal Rachdi and Sou Fujimoto in Paris, won a design competition as part of mayor Anne Hidalgo’s flagship campaign to ‘vegetalise the city’ ahead of the 2024 Paris Olympics.

Straddling the city’s Boulevard Périphérique, the plans for the giant hull-shaped project have been contested. The Parisian administrative court refused planning permission on the basis that the design would in fact funnel toxic air from the expressway towards nearby residential streets, despite the potential positive impact of the trees and planting on the site. Now, an appeal is being considered against the judges’ ruling.

Meanwhile, on a different scale, the site of Heatherwick Studio’s award-winning Maggie’s cancer treatment centre in Leeds is humble, but challenging: a steep grassy hill next to a hospital car park, the last remaining patch of green in an otherwise hard and functional landscape.

Aiming to create more green space than it takes away, the design features a native woodland garden oasis based around three timber pavilions, each on different levels, using prefabricated timber, breathable healthy materials and energy-saving techniques. The end result is a welcoming, healthy environment that has increased biodiversity on the site by 436%.

In the US, the non-profit Friends of Trees has supported communities in the Pacific Northwest area to plant over 870,000 native trees and shrubs since 1989. This is more than just landscape architecture: the organisation prioritises community engagement, using a design process that is participatory, educational and fun. 

In Portland’s Jade District, where one project has been running, there is a high percentage of Vietnamese, Cantonese and Mandarin speakers. Speaking to Yale Climate Connections, project organiser Haley Miller explains that imposing tree planting without community buy-in is simply not effective: ‘I think folks have been sceptical of … having someone come to their door, speaking in English and telling them “You need trees for these reasons.”’

Projects are set up and run by local people, which means the trees are more likely to live a long, healthy life: ‘It needs … some sort of sense of responsibility and excitement for the care of those trees and making sure they continue to thrive well into maturity.’

So how do we capture these lessons and insights? Philipp Nedomlel, a landscape architect at Heatherwick Studio, attempts it here:

‘Each project needs to build in a research and procurement period to find the right species. It’s about the right tree in the right place. Obviously, you should use varieties which are local or native – don’t ship in trees from far away. Think hard about maintenance, especially in the first three years: irrigation, drainage, and space – especially soil volume and width – for the roots to spread.

Above all, understand that trees take decades to mature. It’s about investing in other people’s futures.’