China’s urban vertical forest
Nanjing’s vertical forest will make it easier to breathe in the polluted city – and the towers look pretty too!
AMID the urban sprawl they rise like a breath of fresh air: two soaring towers bedecked in trees and shrubs. These are the forests of the future – and the future has arrived in Nanjing, China. But the leafy tower blocks are not just there to look pretty. They’re China’s answer to a choked metropolis of more than eight million people, a city that has run out of land to plant new trees and where city planners face a growing battle to improve air quality and fight pollution.
The city’s first two vertical forests are under construction and will be completed by next year. They were designed by Italian architect Stefano Boeri and will introduce thousands of trees and shrubs into the bustling city’s densely populated Pukou District, absorbing tons of carbon dioxide and producing oxygen at the same time.
The project serves as a prototype for Boeri’s designs in other smog-filled Chinese cities, including Shanghai, Guizhou, Shijiazhuang, Liuzhou and Chongqing. The country’s cities have such bad air quality that only one percent of China’s 560 million city dwellers breathe air considered safe by European Union standards, a World Bank study has found.
The main causes of pollution are heavy industry, metal smelters and coal-fired power plants, all critical to keeping China’s rapidly growing economy going.
The greenery-laden towers – one 200 m and the other 107 m tall – will help Nanjing residents to breathe a little bit easier. Preliminary estimates suggest the buildings will absorb 25 tons of carbon dioxide each year and generate 60 kg of oxygen a day.
This is all thanks to 1 100 trees – all from 23 local species – and 2 500 shrubs and plants sprouting from the outer walls of the buildings.
The towers, the first of their kind in Asia, will have an array of functions.
The smaller of the two has already been designed as a Hyatt hotel with 250 rooms and complete with rooftop pool, while the larger block will house a museum and a rooftop club, as well as a school of ecological architecture dedicated to sustainable design.
NANJING’S city forest isn’t the first of its kind. Bosco Verticale (Italian for “vertical forest”) is a pair of residential towers in the Porta Nuova district of Milan, Italy. Also the brainchild of Boeri, the buildings are 111 m and 76 m tall respectively and home to more than 900 trees (about 550 in the first and 350 in the second) growing on 8 900 m² of terraces.
Boeri, concerned about climate change and the rapid pace of urbanisation, says his inspiration for the towers came from a tree-laden 14th century tower in Lucca, Italy.
“Hundreds of new skyscrapers were simultaneously sprouting up in cities such as Dubai or Abu Dhabi, and all were covered by glass panels. Knowing about climate change, and many other things, I was not exactly in favour of this choice,” the architect explains.
“Glass reflects sunlight onto the ground, heating up cities. It’s an amazing material, but glass isn’t the best when you have to deal with air-conditioning and internal energy consumption.
“A city should grow within itself, by substituting obsolete buildings, by creating buildings that develop upwards with the inclusion of natural features, just as we’ve done with the vertical forest.”
Given their unusual surroundings, the choice of trees to be planted is important. The species used in the Milan project were carefully chosen by a team of botanists to fit with their positioning on the façades in terms of height.
Plants earmarked for the towers were pre-cultivated and grown specifically for this purpose – in conditions similar to those on the towers – then replanted in the terraces.
Construction for the towers, which have since won architectural awards, began in 2009 and was completed in 2014.
“Day by day, hour by hour, we have a system that checks at any moment the growth of the trees, the irrigation, the condition of the soil,” explains Boeri, adding that the team expected the trees to die out more quickly, but have been pleasantly surprised.
“We also have gardeners and climbers who come out twice a year to cut and maintain the trees.”
Each of the Italian towers would be equivalent to a forest area of 7 000 m² on the ground – roughly the same size as a soccer field.
But more than combating climate change, the towers – which also feature in BBC’s documentary series Planet Earth II – are doing their bit for the animal kingdom.
“We not only have 100 different species of plants, we also have 22 species of birds that nest on the two towers,” Boeri says.
“It’s important to see birds coming back to Milan.”
As well as their health and conservation benefits, the towers add eye candy to the stark city skyline. The living façade means the buildings will constantly evolve and colours will change with the seasons.
One thing’s for sure, urban gardeners of the future had better have a head for heights.
‘Gardeners and climbers cut and maintain the trees’