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Adventures in vertical forests

A worker tends to the vertical gardens

A new movement is gathering pace in the world of landscape architecture and design – the planting of vertical forests and the greening of buildings. A once radical and experimental idea which started in the centre of Milan is now gaining commissions around the world.

Unique projects such as these need the best agronomists to breath life into them. Laura Gatti, the highly respected Italian agronomist, worked alongside Stefano Boeri on the first vertical forest of its kind the Bosco Verticale brought to life by the Boeri Studio in Milan.

Gatti was involved from the beginning in the plant science and planting plans for the Bosco Verticale and is currently working on Studio Boeri’s other vertical woodland projects in China, Switzerland and Holland. As we move towards 2050 and the frightening statistic that 70% of the world’s population will dwell in urban areas and cities there’s no greater need to address the lungs of our cities be they horizontal or vertical.

The Bosco Verticale in the Porta Nuova Isola area of Milan consists of two towers of 80 and 112 metres, hosting 480 large and medium trees, 300 small trees, 15,000 perennial and covering plants and 5,000 shrubs. The equivalent – over an urban surface of 1,700 m2 – of 20,000 m2 of forest and undergrowth.

The Bosco Verticale was designed to increase biodiversity by creating an attractive space for birds and insects, to help build a microclimate (which would enable residents to enjoy the cool shade of the trees on their balconies) and create a diverse palate of plants that would help to absorb CO2 and particles and produce oxygen while simultaneously providing protection from the sun and noise pollution.

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Gatti is passionate about her work and the science that underpins it and says: “I have made a personal commitment to green every surface – because it’s down to us as urban dwellers to solve the problems we create in the cities.”

The process is complicated and there are endless check-lists and answers to be found to multiple client questions too, but plants and trees are at the heart and the very start of the process. “We were there from the very beginning of the design process and the beginning started with the tree – it was at the centre of everything. We had lots of issues that we had to solve and consider. We undertook a two-year feasibility study and mocked up the design, all the time sharing our concerns with people experienced enough to identify the best solutions. We then had to take into consideration the needs of the client and to make sure we were doing all they asked of us.”

Choosing the right plant for the right place was central to the design process. Gatti says: “We were looking for species that had the ability to withstand conditions such as wind pressure on crowns, had a low sensitivity to pests and diseases, plants that would enjoy container cultivation and also required low maintenance. We had to consider using plants that would not be allergenic or poisonous to inhabitants and would have the capability to mitigate air pollution and provide relief from audio pollution too.”

One of the questions that has arisen over and over in response to the Bosco Verticale project is: ‘How will you deal with the problem of tree roots and what kind of maintenance will be required on the project going forward?’

Gatti is at pains to underline how important the choice of species is to the success of the design: “If a tree is OK, if it has no problems then it will have no reason to destroy anything – a tree will become destructive if it is looking for water, oxygen or nutrients, so if we provide the trees with the air, soil and water it needs then the roots will not cause a problem. We also obviously chose specimens who don’t have aggressive root systems.”

This meant that Gatti did not shy away from big trees and selected Mediterranean Ash, Green oaks Quercus ilex, and lots of flowering cherries to go alongside small magnolias and olive trees. The design team worked on a detailed maintenance brief at the start of the project which ran for five years. Gatti and her associates continue to monitor the towers and advise on maintenance, which is carried out by a team of expert gardeners.

The monitoring of the towers has also generated preliminary studies on the mitigating effects of the design and build on air and noise pollution. Gatti and her colleagues at the Univeristy of Milan undertook many preliminary studies during and following the build and are now about to embark on a more detailed study into the effects of the design on biodiverstiy and pollution. And while the Bosco Verticale was designed with biodiversity and climate change at its heart, the project has delivered so much more for the community who live in the vicinity.

Gatti says: “We have been monitoring the Bosco for the last five years and one of the most remarkable findings is the way that the towers of trees have helped connect not only the residents, but also Milano’s citizens, with the cycle of natures. The residents have a living picture of nature before them as they see the changing season happen in front and around them; they see the birds come to nest, the trees flowering, the trees changing colour and the the leaves falling. Most city dwellers become disconnected from nature but the residents of the Bosco feel as though they own the trees, they have a relationships with them and respond to them. A sense of community has been created through this shared relationship with nature as it’s displayed through the life cycle of the trees and plants as they grow and flower on the Bosco.”

In the next couple of years, it is hoped that the city of Najing in China will be ablaze with verdant colour and lots of it as the balconies and vertical surfaces of office blocks, hotels and homes are planted with shrubbery and trees in an attempt to mitigate the toxic pollution faced by its inhabitants. Laura Gatti is working again with the Boeri Studio to make this vision a reality. The Boeri team estimates that the the buildings will suck 25 tons of carbon dioxide from Nanjing’s air each year and produce about 60 kg of oxygen every day.

Ninety-four different species of trees and plants were used in Milan and there are plans to utilise 25,000 plants across two towers in Najing in China, and Gatti sources her plants as locally as possible. This has produced its own trials and tribulations in China where the market is described by Gatti as “very different’ to Europe. The quality of the trees and plants is crucial. Gatti says: “For the new project in China I spent weeks sourcing the right material. The quality is paramount and after three or four attempts I have now found a good nursery in China that I’m working with – and we have learned a lot from each other in the process far.”

The topic of social housing and how best we can serve the community has taken on added gravitas and urgency in the wake of the Grenfell Tower disaster in London. The media has called into question how we build our communities, the materials we use and how we value our residents. The projects in Milan, China and Switzerland are standard bearers for quality and put the residents experience at the centre of the design. With a new commission for a social housing project in Holland this vision of providing a green system capable of cleaning the city air is becoming a reality.

Nick Coslett, marketing manager at Palmstead Nurseries in Kent has invited Laura Gatti to speak at Palmstead’s 10th Soft Landscape Workshop in January next year. Nick Coslett said: “Laura’s work with The Boeri Studios in Milan, China and Switzerland is very thought provoking and timely for the landscape industry. The Bosco Verticale is a very clever horticultural project which uses plants in an interesting way to make life better for the population. It’s an excellent example of good design and practice and I’m sure our delegates will be very interested in Laura’s research and the secrets to long term survival of such a project.”

About Vikki Rimmer

Michael is the editor of Landscape Insight magazine. He draws from experience at a wide range of B2B magazines, including Management Today, Legal Business, Retail Week, Hotel Owner and Jewellery Focus. Feel free to drop him a line with any stories or feature ideas.

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