Vertical forest: evolving nature's role in the urban environment

29 May 2013



A high-rise development nearing completion in Milan represents a major milestone in the integration of nature and the urban environment. Phin Foster looks at the potential impact of Boeri Studio’s Bosco Verticale and asks whether it represents a step change in high-density living.


Architects, planners and citizenry have been reacting to urban sprawl and the cannibalisation of green space since long before sustainability and environmentalism became touchstones of the debate surrounding built environments. The UK's garden city movement, driven by Ebenezer Howard from the late 19th century, was perhaps the first large-scale interventionist response to an increasingly urgent issue.

"It is well-nigh universally agreed by men of all parties, not only in England, but all over Europe and America and our colonies, that it is deeply to be deplored that the people should continue to stream into the already over-crowded cities," Howard wrote in 1898's To-morrow: a Peaceful Path to Real Reform.

His answer was a cluster of several green settlements, satellites of a much larger urban area linked by road and rail; the first of these garden cities to be fully realised was Letchworth, a little over 30 miles north of London.

But Howard's response to mass-urbanisation not only suffered through a lack of government support and financing, it also amounted to an outright rejection of the mega city - a trend that, even by the early 20th century, was becoming something of an inevitability. By most metrics, Howard's abhorred London was the largest metropolis on Earth until the 1920s, but it was the city that inherited the mantle that was to establish a prototype for much of the urbanism witnessed in the second half of the century.

Ideal marriage

In New York, architects were building upwards rather than outwards. Advancements in high-rise building techniques allowed for a level of population density unprecedented in the city since the clearance of the extensive slums that accompanied mass European immigration.

Howard had attempted to combine the town and country to forge a harmonised marriage that acknowledged the power of the city while enabling its workforce to remain connected to a pastoral, some might say idealised, heritage. Instead, a consensus began to emerge that for cities to be sustainable they must be compact and highly dense.

"An increasing number of architects are seeking to blur the lines between nature and architecture within a fully urban context."

Population trends in the developed and developing worlds have only solidified this stance. In 2007, the UN reported that the majority of the world's population had, for the first time, tipped from rural to urban. Having people living in higher densities is no longer merely beneficial within the context of megascale; it's essential.

But density comes at a cost. Critics have lamented an absence of community engendered by high-density living, as well as a notable absence of green space. Architects have countered this though pioneering twists on the traditional tower block. Moshe Safdie, creator of one of the earlier pioneering works in this field, Montreal's Habitat '67, has been one of the leading proponents of 'the humanisation of mega scale' for almost four decades.

"People claim today's social arrangements, the polarisation of rich and poor, and the development of electronic communications all work against this notion of community," he explains. "But you can't tell me that such polarisation did not exist in 19th-century Paris."

Milanese heights

But can pastoralists and pragmatists find common ground? An increasing number of architects are seeking to blur the lines between nature and architecture within a fully urban context. Pioneers such as Edouard François, godfather of the increasingly prevalent green façade, and Ken Yeang have demonstrated the possibilities for the densification of nature within the city. Now, a project nearing completion in the Garibaldi Repubblica district of Milan promises to incorporate
the demands of both camps like never before.

"The project could potentially serve as a blueprint for the survival of European cities."

Dubbed "the most exciting new tower in the world" by the Financial Times, Bosco Verticale - or vertical forest - is two residential towers designed by the Boeri Studio. The project aims to contribute towards metropolitan reforestation and urban diversity, using vertical urban densification to save land and promote sustainable living. The cost of construction is said to be just 5% more than that of a traditional skyscraper.

Bosco Verticale seeks to create a biological habitat and increase biodiversity, developing an ecosystem linking urban life and nature. Lead architect Stefano Boeri has claimed that the project could potentially serve as a blueprint for the survival of European cities such as Milan, faced with the ever-increasing danger of pollution and diminishing vegetation; vertical forests could create a network of environmental corridors and increase green spaces in the city.

The two residential towers are 110m and 80m in height, spread over 27 storeys across a total built-up area of 40,000m². Apartments range from compact two-room dwellings to penthouses and duplexes.

So far so normal, but the balconies of these buildings are 28cm-thick and extend outwards for 3.35m in an irregular manner. They are made of reinforced concrete and will house 900 trees, including
oaks and amelanchiers, 5,000 shrubs and 11,000 floral plants.

"Vertical forests could create a network of environmental corridors and increase green spaces"

The heights of the plants will be in the range of 3-9m and overall plant life for each tower will equate to 10,000m² of forest. This is more than your traditional green façade; this is nature entering the built environment.

Vegetation will protect the area from the harsh Mediterranean sun during summer. During winter, the trees will allow sunlight to warm the interiors. The plants will also be home to various insects, birds and animals.

A large variety of fauna has been selected in order to render different shades on each building's façades. Furthermore, the vegetation creates a system that optimises, recuperates and produces energy, aiding in the creation of a microclimate and filtering dust particles. The diversity of the plants and their characteristics produce humidity, absorb CO2 and dust particles, emit oxygen, and protect from radiation and acoustic pollution. The plants will be irrigated using grey water produced in the buildings and photovoltaic systems are being installed to improve energy self-sufficiency.

Distant echoes

The development is part of the BioMilano and accounts for one of six projects aimed at increasing the number of green spaces in Milan, establishing "transitional states between the city, nature
and agriculture".

"Milan, like every city in the world, today, is at a crossroads," says Boeri. "It can continue growing by eating up agricultural land, woods, natural space, and thus reducing biodiversity and the space available to other species. Or it can choose to become a biodiverse metropolis, starting with a new agreement among the city, the natural world and agriculture."

His solution might appear somewhat different to that conceived by Ebenezer Howard, but one can still envisage the early urban reformer nodding sagely in agreement.

The two towers of the Bosco Verticale project in Milan, Italy.
Bosco Verticale uses vertical urban densification to save land and promote sustainable living.
The vegetation used in Bosco Verticale will create a microclimate.


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