'Vertical forest' to help clear air

Architect Stefano Boeri stands in front of the world's first "vertical forest" in Milan in August. FOTOGRAMMA?

Asia's first "vertical forest", which helps reduce air pollution and save energy, will be built in Nanjing, Jiangsu province, next year.

The project, the world's third, will consist of two tower blocks in Jiangbei New District whose facades will be covered with 1,100 trees and 2,500 cascading plants and shrubs.

Those plants will produce about 60 kilograms of oxygen a day and absorb 25 metric tons of carbon dioxide a year, according to Nanjing Yangzi State-Owned Investment Group, an investor in the project.

A 200-meter-tall tower will mainly hold offices, and a 100-meter tower will include a hotel with 247 rooms.

Cai Long, president of Yangzi Group, said the towers' design has been adjusted to allow the balconies to support the weight of trees that can grow to 9 meters high.

"Each tree planted on the balconies will be tested in a wind tunnel to prove it can remain vertical in storms," Cai said.

He said the vertical forest has many advantages, including regulating microclimate environment, isolating noise and reducing the heat flows between buildings and the outside environment.

Zhou Qi, a professor at Southeast University's Architecture School, said the high cost of construction and maintenance will prevent vertical forests from developing rapidly.

"Growing trees will greatly raise the cost of construction materials and labor," he said. "Generally, five to six protective layers are needed to stand up to water and the strength of plant roots."

The nutrition of the trees, the conservation of soil and water will also be expensive after the towers are put into use, he added.

Cai said: "The vertical forest is a method to cope with the massive environmental crisis.

"Instead of horizontal expansion, it allows the cities to grow vertically and reduce pollution as well as energy consumption with multiple trees and other kinds of plants."

According to the website of Italian architect Stefano Boeri, the designer of the vertical forest, some other Chinese cities have shown interest in the idea.

The world's first vertical forest was built in Milan, Italy, in 2014.

Luis Pimentel, public relation manager of Stefano Boeri Architects, said "the most important function of the vertical forest is to battle climate change in the place where it is produced, that is, cities."