Forward-thinking architects are coming around to the view that inner-city tower blocks and woodland can be combined and are incorporating both in their latest designs.
Plans for "vertical forests" – 25-floor buildings, flecked with balconies full of bushes and small trees – are sprouting up in several European countries.
Fittingly, Milan, the continent's design capital but also one of western Europe's most polluted cities, is leading the way with the construction of two green towers. The Bosco Verticale (vertical wood) project, due to be completed in 2015, consists of two residential blocks, 110 metres and 76 metres in height, set in the Isola neighbourhood just north of the city centre. The towers will house a total of 900 trees, ranging from 3m to 9m in height, plus thousands of shrubs and flowering plants.
Stefano Boeri, the architect responsible for the design, says that together the buildings will provide the city with the equivalent of a further 10,000 square metres of woodland. The layer of foliage around the apartments is supposed to produce humidity, absorb CO2 and dust particles, produce oxygen and shield the building from traffic noise. Energy recycling systems that generate power from sunlight and wind should produce "dramatic" energy savings. The designers say that the plants provide shade in the summer and allow more light through during the winter months after they have shed their leaves.
But all that environmental technology doesn't come cheap. Prices at the exclusive development will start at €750,000 for 100 square metres, near the ground, rising to €1.2m for flats with spectacular views across the city.
"The towers may well be beautiful, but they are not something everyone can afford," said Damiano di Simine, regional president of the environmental campaign group Legambiente. "The real answers to Milan's pollution problems lie with sorting out the traffic problems and improving public transport."
Michele Brunello, an architect working with Stefano Boeri, agreed that the apartments under construction were at the luxury end of the market. "In this area, being so central, they're bound to be expensive," he said. "But the fact that these apartments cost a lot doesn't mean this project is not a good thing in an environmental sense.
"By highlighting how the use of plants and trees can make the environment healthier and more beautiful maybe we can encourage similar developments elsewhere."
And Milan's residents certainly know that new ideas are needed: thick smog regularly envelops the city and its levels of toxic PM 10 soot frequently breach EU safety levels.
Architects in other populous, compact continental cities with chronic traffic and pollution problems are also turning to green skyscrapers to help the environment. In Valencia the planned Torre Huerta will feature balconies with trees and the use of solar cells. In Barcelona, the helical Stairscraper, in which the roof of each apartment will house the garden of the dwelling above it, is due for completion by the end of 2015.
But the problem of how to keep the foliage looking good – and doing its job– has yet to be resolved. Mr Brunello said plans for gardeners to descend, like window cleaners, on rigs outside the Bosco Verticale are being ditched in favour of "garden-freeclimbers" – think Spiderman armed with clippers and green-fly spray.