A home for trees and birds, and also humans': How high-rise forests can transform city life – and make us happier

In 2007, Italian architect Stefano Boeri witnessed the frantic construction of a city in the Dubai desert dominated by energy-wasting skyscrapers covered in glass, ceramic and metal. All these materials, he tells the BBC, "reflected sunlight, generating heat in the air and especially on the urban ground, where pedestrians walked". Three thousand miles away, he had just begun working on his own design for two very tall buildings in a neglected area of northern Milan. "Suddenly, it occurred to me to create two biological towers… covered not with glass, but with leaves," he says. The design would invite fauna and flora into this industrial wasteland and cool the air inside and out, offering a radical new architectural prototype that, he explains, "integrates living nature as a constitutive part of it". The startling result was the world's first "vertical forest".