Looking at a photograph of downtown Milan, Italy, one's eye is caught by what looks like a couple of highrise apartment towers. Heavily forested towers.
The towers opened just three years ago and the trees that adorn every horizontal surface of the buildings' exteriors have grown enough sprouted new branches that the buildings themselves have begun to disappear from view.
It's appropriate, therefore, that the two-tower project was dubbed the Bosco Verticale — Vertical Forest — by its architect, Stefano Boeri.
This forest uses more than 20,000 trees and plants. Cherry, apple and olive trees spill over balconies alongside beeches and larches, selected and positioned according to their resistance to wind and preference for sunlight or humidity.
And now Boeri's idea is being exported to about a dozen cities around the world, from Lausanne in Switzerland to Sao Paolo in Brazil to Tirana in Albania.
Boeri says the idea of the vertical forest came from his obsession with trees and a determination to make them "an essential component of architecture," particularly as a weapon to combat climate change.
"I was in Dubai in 2007 and I watched the city growing in the middle of the desert, with more than 200 glass towers multiplying the effect of heat," he recalls.
As a result, he decided to create something that "as well as welcoming life, can contribute to reducing pollution because trees absorb microparticles and carbon dioxide."
It wasn't simple.
Boeri and his team had to figure out how the balcony should be structured to carry the weight of the plants, how to secure the tree roots and what kind of mix needed to go into the soil. He also worked closely with botanists to create a nursery of a thousand trees that had been trained to grow under specific conditions.
"Now," he says, "for every human being living in the building, there are about two trees, 10 shrubs and 40 other plants."
On top of that, there are a lot of nesting birds.
The apartments in the towers could, I guess, be called luxurious, selling for around $16,000 per square metre.
But the Dutch city of Eindhoven is considering building a Vertical Forest for social housing — a project Boeri says he's especially keen on.
He's also got a lot of work underway and planned in China. There are two towers under construction in Nanjing and a hotel is in the works for Shanghai. And China has plans for a "Forest City" of some 200 buildings in Liuzhou.
All of this is happening because of the realization, especially in China, that air pollution has become a dramatic problem and that uncontrolled urbanization as people move to cities is something that needs to be addressed.
All this fits in nicely with the research report from the Nature Conservancy that I wrote about recently.
The report, Funding Trees for Health, has attracted little attention in the mass media but sparked a fair bit of discussion in professional circles. It was featured on the website of the American Society of Landscape Architects.
That group was especially taken with the idea that for just $8 per person, the United States could maintain and then significantly expand the tree canopy of American cities, an idea that would be "an incredibly cost-effective investment in public health."
Louisville, Ky. is one city that is trying to use trees as a health measure.
There, a wall of mature trees and shrubbery has been planted in the front lawn of a school, forming a wall between the school and a busy nearby street.
The project, called Green For Good, will evaluate the notion that a wall of greenery can improve air quality, and thus student health. It's a small first step, but one that could help establish the concept of urban trees as part of urban infrastructure.
Korky Koroluk is an Ottawa-based freelance writer. Send comments to firstname.lastname@example.org.