Boeri and the trees

In an act of pre-adolescent rebellion, 12-year-old Baron Cosimo Piovasco di Rondó – the protagonist in Italo Calvino’s The Baron in the Trees – abandons his oppressive family by climbing a tree and vowing to spend the rest of his life among the branches. Today, in an effort to combat climate change, Italian architect Stefano Boeri is doing just the opposite – he’s bringing the trees to the people.

With a twinkle in his eye and a pair of eyeglasses propped on his forehead – his personal trademark – Stefano Boeri proclaims: “I’ve always been obsessed with trees.” This fascination dates back to his childhood, when his mother, also an architect, built a house in the woods near Milan. Designed “to embrace the trees,” as Boeri puts it, the construction avoided the felling of trees, resulting in the home’s meandering layout.

At roughly the same time, Boeri read Italo Calvino’s novel The Baron in the Trees. Set near his father’s ancestral hometown of Badalucco, the novel’s rich descriptions of olive trees and lush orchards captured a young Boeri’s imagination. Of course, he may have also been drawn to Cosimo’s rebellious streak and penchant for radical, irreversible decisions. Years later, Italian singer Adriano Celentano’s Un Albero di Trenta Piani decried the skies blackened by factories but ended on a hopeful note with visions of a thirty-storey tree.

A desert epiphany

All of these memories must have been at the back of Boeri’s mind when, during a trip to Dubai he was struck by the dozens of skyscrapers rising from the desert, completely covered with glass that reflected the sun’s heat onto the pedestrians below. “It seemed like a paradox to me,” he says. It was 2007 and Boeri was in the early stages of designing a pair of residential towers in Milan when the idea occurred to him quite naturally: “Why don’t we create a biological ecosystem in a high rise building instead of covering it with glass?” and the Vertical Forest was born.

Completed in 2014 and standing 110 and 76 metres tall respectively, the two towers are now home to over 20 000 plants including trees and shrubs, and over 20 species of birds. During the summer, shade from the trees keeps the apartments approximately three degrees cooler than the outdoors, eliminating the need for air conditioning. Boeri describes his Vertical Forest as “a prototype of a new generation of buildings that will help cities clean their air, absorb CO2 and other pollutants, and reduce energy consumption. So there’s a social utility in what we have done, which is very important for us.”

Convincing the sceptics

But building the first Vertical Forest did not come without challenges. Boeri was surrounded by sceptics along the way who questioned the feasibility of his seemingly crazy idea. How would the trees survive in windy conditions? How could the balconies support the weight of the trees? How would the plants be watered? Would the roots damage the buildings’ structure?

To convince the detractors, Boeri set out to work with a multidisciplinary team of botanists, engineers and architects, and he believes they came up with good solutions for each of the technical challenges. Careful thought and research determined the selection and placement of each plant. The balconies that host the greenery were specifically designed and positioned to give the trees enough room to grow and give plants the ideal amount of sunlight according to each species’ needs. For each new iteration of the Vertical Forest being built elsewhere, this research process begins anew to take into account the climatic conditions and species native to each location: “I like to say that I’m designing a house for the trees. But humans happen to live there, too.”

When it comes to maintenance, “we have worked so hard to make sure the plants are well cared for,” he explains. The trees are watered using a sophisticated Israeli irrigation system, which also recycles the buildings’ greywater. A central monitoring system tracks moisture levels and the plants’ overall condition. To avoid the use of pesticides, ladybirds were introduced to control pests. And, he adds proudly, “we have invented a new profession – the flying gardeners.” Three times a year, a team of flying gardeners dangle from the top of the buildings to inspect and prune the plants.

The culprit and the solution to climate change

Boeri wasn’t always driven by purely environmental motives, “but at a certain moment in my life, these two things – trees and architecture – came together, and I could see how this vertical forest approach could help me and my firm to improve the quality of our architecture, transforming the relationship between humans and trees within an urban centre.”

Speaking at lectures around the world, he frequently points out that cities cover less than 3 per cent of the Earth’s surface, but produce 75 per cent of the planet’s CO2 emissions. Cities are primarily responsible for climate change, but are also the first to feel its effects through coastal flooding and the migratory influx of climate refugees. Therefore, cities must play a role in combatting climate change. How? The easy answer, of course, would be to plant more trees and expand parkland in our cities. But this isn’t easy in densely packed urban centres with a lack of open spaces. Enter the Vertical Forest, which Boeri argues helps prevent urban sprawl by allowing people to live close to trees and plants in a crowded city – something that normally is only feasible in suburban environments.

The concept of rooftop gardens is not entirely new, however. After all, Austrian artist and architect Friedensreich Hundertwasser – another one of Boeri’s early inspirations – was ahead of his time when he sketched out plans for apartment blocks that featured a grass-covered roof and trees growing from inside the rooms back in the 1970s. But what is truly revolutionary about Stefano Boeri’s Vertical Forest, is the density of a complex ecosystem on a relatively small footprint—the equivalent of 2 hectares of woodland. “If you really want cities to be part of the solution to global warming,” he explains, “it’s not enough to work only with horizontal surfaces. You need to work with vertical surfaces as well.”

Green housing for all

Boeri concedes that an apartment in Milan’s Vertical Forest might be out of reach for most people, but the towers needed to compensate the developers who took on the risk of investing in his architectural experiment. So he has now set his sights on affordable housing for lower-income urban dwellers. Boeri and his team have found ways to reduce the construction costs of his Vertical Forests, and the first of these green social housing projects is currently underway in Eindhoven. “This means that we can combine our capacity to deal with climate change with our capacity to deal with poverty,” he says.   

But Boeri’s most ambitious project is in China, which is notorious for its poor air quality. Consisting of over 70 plant-covered buildings connected by parks and gardens covering 175 hectares along the Liujian River, the Forest City in China will be home to 30 000 residents. In addition to absorbing 10 000 tonnes of CO2 per year, the Forest City will rely on geothermal and solar energy, making it energy self-sufficient. Ultimately, Boeri hopes to see more Vertical Forests replicated throughout the world. “We have not copyrighted the solution because we hope that there will be other architects who can do better than us.”

Beyond the environmental benefits, is the sense of well-being that residents get from living in the Vertical Forest. “The feedback we hear from people living there is extremely positive.” Residents can look out of the window and see the world filtered through the leaves and observe the changing colours of the seasons. “When you live on say, the twenty-third floor of the building,” Boeri continues, “you feel as though you are in the forest.” Would Cosimo consider living in the Vertical Forest? “Ah, that is a very good question. I don’t know about Cosimo,” he ponders. “But I think Italo Calvino would live there.”

Video production: Scott McNamara, Fabio Kobel

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