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The Secrets of Vertical Forests

The interview with Laura Gatti, landscape curator of the greenery which will cover the futuristic skyscrapers

In a few months, in Milan, there will be two new buildings that change colour every day. And which will lose their leaves in autumn. Let’s take 700 large and small trees, 20 thousand plants ranging among drooping, ground cover and herbaceous perennials, plus another 4 thousand shrubs and flowering bushes. If spread over a flat surface, these numbers would be sufficient to cover one hectare of land.
In the Isola district, instead, just north of the centre of the capital of Lombardy, this same plant list will be distributed in height, along the external facades of two 26 and 18-floor residential towers, designed by Studio Boeri and grouped under the name of Bosco Verticale (Vertical Forest). While the works of the yard have entered their final phase, a few weeks ago we followed the first, spectacular plantings, dozens of metres above the ground.
Laura Gatti is the landscape agronomist who, together with Emanuela Borio, has taken care of the green area of the “most exciting new building in the world”, as it was defined a few months ago by an influential
British newspaper. In recent years, Gatti has selected plants suitable to withstand extreme environmental conditions and has solved exceedingly tangled technical and logistical issues, reconciling botanical and engineering requirements. We asked her to unveil the secrets of the Vertical Forest, which at the end of spring 2013 should welcome the first tenants (about 40% of the
more than 110 flats in the two towers is still available on the market, for sale at about 9 thousand euro per square metre).

Covering a building with greenery: why?

Because it has many advantages: both for those who will live inside the building, and for those who will go past or live
nearby. The environmental benefits of the Vertical Forest, which will be monitored over time, consist of sound insulation, filtration of fine dust and oxygen production, lowering temperatures during the hottest months, the call of birds to encourage biodiversity. As regards visual benefits, there are studies that show that nature observation produces positive psychological effects on humans: I think it will be so for the Vertical Forest, even more so given that it is located in a very highly-populated area of the city.
Which plants did you choose for the Vertical Forest?
Given the exceptional circumstances, before reaching an aesthetic choice, we were guided by the criterion of resistance: to wind, which at the top of buildings roughly 80 or 110 metres from the ground, is very strong, to pruning and to pests. We discarded allergenic plants, and preferred other ones, easier to maintain, capable of reducing dusts. Then, in order to produce the visual effect of a wood
we selected trees, including holm oaks, trees belonging to the Parrotia family, Turkish hazelnuts, beeches, plum trees. Which however will be a numerical minority, compared with the enormous quantity of smaller plants.

What will the two towers look like at different times of the year?

Of course, this changes according to which way the façade faces. In general, on the south side of the Vertical Forest towers, we have placed evergreen species, very colourful and showy. To the north and west there will be deciduous plants, with autumn hues, while in the east, soft, fresh, spring tones will prevail. The show and the visual effects will be different during each season.

How do you avoid branches or entire trees falling off? How were safety issues dealt with?

Each tree will be anchored to a safety rope, stretched vertically, so that even if the various branches or the trunk should break, they would remain suspended and not fall. In the preliminary phase, all plants were subjected to wind tunnel tests, in Miami, in conditions of extreme stress.
Naturally, we have also carried out checks on the flow and waterproofing of each of the containers holding the five cubic metres of soil which will house the plants, protruding 3 and a half metres from the facade of the towers. There will be greater tensions, in general, on the trees which are planted higher up. But safety is total.
The management of the greenery will be centralised: irrigation, pruning, periodic inspections.

What kind of contact will the people living inside have with the plants?

IThe greenery of the Bosco Verticale will be in communal tenure: this is why it will have to be managed in a centralised manner. It is true that many of the future tenants felt relieved when they learned that they would not have to look after their piece of “forest” personally, but it is also true that these same people, if they wish, can very well take care of small maintenance interventions. as long as they respect the harmony of the common good.

Let’s spare a thought for the consumption of resources and energy to provide water to thousands of plants, dozens of metres above the ground. Is the Forect actually sustainable?

During the project phase, this was one of our main worries. But we can say we have managed to reduce the use of resources to a minimum. Thanks to a system of heat pumps and sensors, the irrigation in the Vertical Forest will exploit non-potable underground water, already used once for air-conditioning systems. In addition, the roof will house solar panels and other geothermal energy systems.

What meaning does the whole project hold for a landscape expert?
It is a significant step towards improving living conditions in Milan. Integrating greenery with buildings is increasingly necessary, and not just as a luxury. Then again, just look around you when you move along the city streets: trees on terraces, luxuriant balconies… The next step will be to do what occurs in many foreign countries, where a green roof, an extraordinary benefit for the building and the urban climate, is not only allowed and looked upon favourably, but is actually mandatory.



di Daniele Belleri

Twitter @dajamog