Are trees on houses and other vertical landscaping useful for cities?

    30 Oct 2021

    Vertical landscaping has emerged in response to climate challenges in densely populated cities, often lacking trees and parks.

    On the ground, trees perform many other functions, in addition to carbon sequestration: drainage and soil strengthening, shading for the street, and so on.

    Green facades and roofs have become increasingly popular – for example, in New York, more than 36 tons of organic vegetables are harvested from rooftop gardens every year. This method allows you to cool the thermal islands, create shade, improve air quality, absorb carbon emissions, increase biodiversity, and, ultimately, it’s just beautiful.

    However, vertical landscaping – especially the vertical woods on the facades of buildings – has another side of the coin, which draws the attention of ArchDaily.

    Commenting on the project of the green skyscraper Bosco Verticale in Milan, architect Lloyd Alter notes that the opportunities for tree growth on the facade are limited. Atmospheric conditions at altitude and lack of space for root growth can affect plant health. He admits that the house looks very impressive but reminds us that the reality often differs from the renderings.

    In particular, skepticism is caused by the fact that the placement of wood on the facade requires reinforced structures that will provide it with space for growth and withstand the weight of the soil and the tree itself. Therefore, the vertical forest on a skyscraper requires a larger amount of materials, especially concrete, and consequently, higher carbon emissions. It is unknown how many years the tree will be able to absorb this amount of CO2.

    “We have to take back the streets. It is a crime when a person occupies 18 square meters to park his car, when in this area you can grow food for 1400 dollars. Who gave it all to the machines? Maybe we wouldn’t need to invent vertical forests and gardens if we used the horizontal areas of streets and roofs properly?” he asks.

    Tim de Chant, the editor of the popular science publication NOVA, is even sharper in his skepticism about trees on skyscrapers. He suggests remembering that trees avoid growing on top of a mountain. A strong wind breaks the so-called boundary layer – a fragile layer of air between the leaf and the atmosphere, in which gas molecules begin to behave like a liquid.

    “There are many scientific reasons why trees do not grow – and will not grow – on skyscrapers, at least not at the height at which architects paint them. Because life there is lousy. It’s hot, cold, windy, rain and snow splashing in your face at high speed. Trees and the earth are not sweet. I can’t imagine how it is at the height of 150 meters, where every change of weather is more extreme than from below,” he wrote.

    On the ground, trees perform many other functions and carbon sequestration: drainage and soil strengthening, shading for the street, and so on. The publication concludes that vertical landscaping has many advantages but should not replace traditional green areas.

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