Vertical forests

Johannesburg lays claim to being the largest artificially cultivated urban forest in the world, which is great, even if it’s not entirely true. It’s great because it instils a sense of pride in the trees of the city, encouraging citizens and authorities alike to nurture them, and to plant more.

And the Soweto Greening Project is extending that tree-planting spirit with – so far – more than 200,000 trees having been planted in Soweto. Not surprisingly, cities worldwide are becoming more and more creative in their greening efforts, with possibly the most spectacular of these being the innovation of vertical forests. Would this be a good idea here too?

Vertical gardening

Space is becoming a premium everywhere, with houses, apartments and gardens all getting smaller, making vertical gardening almost a no-brainer. Walk into any nursery, and you will find a range of vertical gardening solutions – hanging baskets, wall-mounted planters, decorative planted screens, balancing towers, and more. But these are all on a small scale, and vertical gardening is going big.

Classical precedent

The Seven Wonders of the Ancient World list some of the most spectacular architectural and engineering feats of ancient times, including the Pyramid of Giza (the only one of the wonders that still exists), the Colossus of Rhodes, the Lighthouse of Alexandria, the Mausoleum at Halicarnassus (in what is now Turkey), the Statue of Zeus at Olympia, and the Temple of Artemis at Ephesus. And, even though its actual existence has never been proven, the Hanging Gardens of Babylon. If it existed in fact, rather than only in myth, it was the first known constructed urban vertical forest. It’s tricky – there is no archaeological evidence of its having existed but, if it hadn’t, you’d have to wonder how it got on the list, and who thought up such a thing without ever having seen it. Anyhow, whether it’s true or not, it’s served as an inspiration for innovative architects more than 2,000 years later.

Bosco Verticale – the contemporary pioneer

The first vertical forest skyscraper to be built was Bosco Verticale in Milan, Italy. Designed by Stefano Boeri Architetti, the two towers are characterised by strong, waterproof external terraces that serve as planter boxes for more than 900 trees, and many, many shrubs and flowers, totalling about 20,000 plants altogether. The towers, which are 111 metres and 76 metres high, are mostly residential, with about 400 apartments, but they also house an 11-storey office building.

Why are plants so important?

The plants serve a number of purposes, including just being beautiful and improving quality of life for apartment dwellers, who have a close-up view of trees, flowers, birds and butterflies, but their most important purpose is that they decrease the need for heating and cooling, hence using less energy, and also absorb CO_2. The plants on Bosco Verticale, for example, absorb approximately 20 tons of CO₂ a year.

Sky-high vertical forests around the world

Bosco Verticale was just the first, and – as such – it gave the name to the whole concept, but it’s such a great idea that it’s spawned a slew of similar designs.

Vincent Callebaut Architectures has a number of vertical forests in the planning phase, of which the most likely to be built is the 115-meter-high Rainbow Tree, planned for Cebu in the Philippines. It will be the first timber-frame vertical forest to be built, and also the tallest all-timber building in the world. Naturally, the project will incorporate the latest sustainable design elements such as rainwater harvesting, solar heating, and electricity generation, passive solar heating, and also wind turbines. A rooftop veggie garden will contribute to significantly decreasing food miles.

Also by Vincent Callebaut Architectures, Arboricole was a finalist in the 2018 Imagine Angers competition to reimagine an urban space for the city of Angers. Arboricole features external plantings on its 50-apartment building with a concert hall, hotel, brewery, and restaurants.

Stefano Boeri plans to build Africa’s first vertical forest in Cairo – Jungle City. Consisting of three separate 50-metre-high mostly residential buildings, it’s not as much of a skyscraper as the original Bosco Verticale. The buildings will be enhanced by more than 350 trees and 14,000 shrubs, plants and flowers, most of which will be indigenous to North Africa. It’s estimated that the plants will absorb about seven tons of CO₂ per year, and produce about eight tons of oxygen, thereby contributing positively to addressing global climate change.

Vertical forests in South Africa

There are, as yet, no plans afoot to build vertical forests in South Africa, but an innovative study at the University of Cape Town suggests that the exterior walls of existing and new buildings can be planted up to resemble the ecosystems usually found on natural cliffs. This would provide for less plant matter than the designs so far used for vertical forests, but they would have the advantage of being self-sustaining once they have been established.

And, while there are no actual plans yet, there are dreams of a vertical fynbos building that would have all the advantages of the existing and planned vertical forests plus the added benefit of being water-wise and exquisitely fragrant. Also, imagine regularly spotting iridescent sunbirds flitting about outside your apartment windows – something only residents of the leafier suburbs enjoy at the moment.

If you want to take the fantasy a bit further, imagine these plantings on a building in the shape of Table Mountain – an interesting tying in of one of the ancient Seven Wonders with one of the contemporary natural Seven Wonders.

Wonderful indeed!