AFP: Milan's vertical forests are spreading to the Netherlands and China

photo: Irene Grassi

Milan - More than 20,000 plants and trees, equivalent to two hectares of forest on two buildings: two residential buildings called Bosco Verticale (vertical forest) in Milan have their rivals, and their concept is spreading around the world, from the Netherlands to China. In the Milan district of Porta Nuova, everyone's eyes are on these two green skyscrapers, where several celebrities live, including Croatian footballer Ivan Perišić from Inter Milan.

Larches, cherries, apple trees, olive trees, beeches... Dozens of plants or trees grow on each balcony, arranged according to their resistance to wind and whether they prefer light or moisture. "The project was born from my obsession with trees and thoughts on how they could become an integral part of architecture," architect Stefano Boeri told AFP.

The vertical forest also has its ecological aspect. "In 2007, I was in Dubai and saw a city rising in the middle of the desert, with more than 200 glass towers that amplified the effects of heat," explains the architect. Thus, the idea for a building that would grow and help reduce air pollution in the city was born, as trees absorb particulate matter and carbon dioxide.

"Cities today produce about 75 percent of the carbon dioxide present in the atmosphere. When we add more trees to a city, we are fighting the enemy right at the source," noted Boeri.

The Bosco Verticale project, consisting of two towers standing 110 and 76 meters tall, was born in the autumn of 2014. Other buildings, more or less covered with greenery, exist elsewhere in the world, especially in Singapore or Paris, where Tower Flower stands. However, the originality of Milan's Bosco Verticale with its 20,000 plants and trees earned Boeri the prestigious International Highrise Award in 2014, and in 2015, the Chicago Council on Tall Buildings and Urban Habitat named the Bosco Verticale the most beautiful and innovative building in the world.

"It's amazing to live here; we are in direct contact with the plants, all in the city center and in a super-modern skyscraper," says Simona Pizzi, who can see the mountains from her apartment on the 14th floor. "The plants have developed a lot over the past three years, changing with the seasons," she adds with a smile.

Boeri worked for three years with botanists to create a "nursery" for a thousand trees, which were adapted to grow under specific conditions. Only then were they planted.

Numerous challenges had to be overcome: from the dimensions and structure of balconies and parapets designed to hold the vegetation, to ways of "anchoring" the roots of the trees, to the weight and composition of the soil. Resilience tests were even conducted at a hurricane-specialized center in Miami.

"For every person living in the building, there are about two trees, ten shrubs, and 40 plants," states Boeri. "Something extraordinary has also happened that we did not expect: an incredible number of birds have nested here. We have small falcons and swifts on the roofs that had previously disappeared from Milan," he says.

Boeri and his team are now working on a dozen similar projects around the world: in Lausanne, Switzerland; Utrecht, Netherlands; São Paulo, Brazil; Tirana, Albania; and elsewhere.

In China, two towers are being built in Nanjing, a hotel is planned in Shanghai, and a whole "forest city" with about 200 buildings is expected to rise in Liuzhou. "China is aware of the problem of drastic air pollution. When 15 million rural residents move to cities every year, we need to think about new solutions, new green cities," says Boeri.

Therefore, the architect decided not to patent his vertical forest and even wrote a book describing all the techniques used. "I will be happy if it becomes a way to develop cities," he emphasizes.