In 1972, the streets of Milan, Italy, were a hotbed of politics and protests, and 16-year-old Stefano Boeri was at the center of the action. But as Boeri marched for economic justice, an eccentric street artist named Friedensreich Hundertwasser was preaching a different ideal, one that would inspire the future architect’s vision of sustainable design.
“I remember him holding up a small oak tree in one hand, and he was talking about the trees being considered as houses for tenants,” says Boeri, now 60. “I wasn’t especially interested in ecology, but Hundertwasser was one of the first to observe the relationship between humans and trees from a different perspective, and that was very, very influential.”
Hundertwasser eventually helped design one of Vienna’s most popular tourist attractions, the Hundertwasserhaus, a mixed-use complex with 250 trees and bushes growing inside residences and across the building’s facade.
Boeri went on to study architecture in Milan and earned his PhD from the Istituto Universitario di Architettura in Venice. Today, his Milan-based company, Stefano Boeri Architetti, is one of Italy’s most renowned sustainable design firms. It’s also a pioneer in “Vertical Forests”—buildings that feature hundreds of trees that sprout from balconies, creating an ecosystem of flora and fauna that stretch across the structures’ exteriors. The architect’s leaf-covered creations can be seen in cities across the world, from Switzerland to the Netherlands to China.
Boeri’s flagship Vertical Forest is a $60 million, geothermally heated, Leadership in Energy and Environmental Design (LEED) Gold building in Milan completed in 2014. The solar-paneled residential towers—27 and 19 stories tall—feature 900 trees, each 10 to 30 feet in height. On flat land, that’s equivalent to nearly five acres, or 215,000 square feet of forest. Along with 20,000 shrubs and flowering plants, the greenery creates what Boeri and his team call a microclimate, producing humidity, filtering dust and pollution particulates, absorbing carbon dioxide, and producing oxygen.
In summer months, the Vertical Forest can reduce the building’s surface temperature by 54 degrees Fahrenheit, cooling the inside by as much as 5.4 degrees. And rainwater that would otherwise flow unused to the sewers is recaptured by the building’s vegetation and an advanced irrigation system.
Individually, Boeri’s Vertical Forests make measurable impacts on energy use and the buildings’ immediate surrounds. The Milan towers remove 11 tons of carbon dioxide from the air each year, according to Boeri’s firm.
But the designer’s next project will do much more than build a Vertical Forest on a city block. It will transform Shijiazhuang, China, one of the most polluted urban centers in the world, into a “Forest City.”
“Lung Busting” Pollution
On December 19, 2016, a thick, noxious smog hung over Shijiazhuang, China, shutting down schools and businesses for the city’s 10.7 million residents. The South China Morning Post described the air as “lung busting.” Even inside their homes, citizens could not escape the choking smog from burning coal and car emissions. And it was not an unusual day in Hebei province.
The World Health Organization ranks Shijiazhuang’s air quality 14th among the world’s most polluted cities. On that chilly winter afternoon, the level of PM2.5 and PM10, two of the most toxic airborne particulates for human health, were reportedly more than 1,000 micrograms per cubic meter. The WHO recommends exposure be kept under 25 and 50 micrograms, respectively.
Which is why Stefano Boeri’s plan for Shijiazhuang seems both brilliant and, well, crazy. The Italian architect plans to turn a 556-acre section of the metropolis into a “Forest City,” with dozens of Vertical Forests stretching across five multi-use districts. The idea is to create a borough-sized air purification system for 100,000 city residents. Based on the data from Boeri’s one-off Vertical Forests in Milan and elsewhere, the Forest City could have a massive impact, removing tons of carbon dioxide from Shijiazhuang’s air and reducing the levels of toxic particulates to safe, habitable levels.
“Every year in China, 14 million people abandon the countryside for the city,” says Boeri, “and Shijiazhuang is the result. It’s one of many megalopolises where public policies are creating a nightmare in terms of environmental impact and quality of life, and [the Chinese government is] now seriously considering the consequences of their planning.”
Boeri’s team is currently exploring locations but has not announced a construction date or budget for the project, branded ForestCityShijiazhuang. He says it will likely strive for LEED certification.
The development will be built on just under one square mile of Shijiazhuang and focus on vertical density. Shijiazhuang proper spans 825 square miles and is the largest city in northern China’s Hebei province—almost three times the size of New York City. That urban sprawl has multiplied the impact of development and pollution across the landscape.
The master plan calls for five petal-shaped districts, each housing 20,000 residents in mid- and high-rise buildings. The petals surround a central park with a hospital, school, and cultural activities, but each multi-use district will provide nearly every amenity to residents: commercial, retail, public spaces, and gardens. The result is a reduction in both urban sprawl and the pollution that comes from transportation.
The centerpieces in Boeri’s master plan, though—and what distinguishes it from other multi-use urban developments—are the Vertical Forests themselves. Based on each Vertical Forest’s green cover and the design’s scale, the project could create millions of square feet of forest, all within one square mile of city space. Boeri’s hope is to use ForestCityShijiazhuang as a prototype and replicate the design in polluted cities around the world.