Not so supertrees after all

Cities may never provide havens for the natural world

In the final episode of David Attenborough’s Planet Earth II, after a depressing presentation of the disasters which befall living organisms on account of our cities, the focus shifted to a bright hope of a green future for urban environments. We were presented with the world’s first ‘vertical forests’ in Milan, two residential towers housing trees on their balconies. Next we saw the green infrastructure of the city of Singapore, with ‘supertrees’—artificial solar-powered structures—packed with plants, providing niches for thousands of animals and allowing life to return to the city.

The reversal these changes represented initially filled me with a warm glow of hope, and began to dissolve my despair over our species’ destructive effect.  However, I have come to believe that these great plans for a green urban future are no substitute for traditional methods of saving and sustaining the natural world.

The first issue with growing trees on skycrapers is the large amount of concrete that must be produced to support the weight of a tree. Producing this concrete is likely to release more carbon dioxide into the atmosphere than the tree will ever absorb. This doesn’t sound very green. Equally damning is the fact that the biology of a tree is far from conducive to living on a skyscraper. Where will roots grow on top of a building? Also, the exposure to the elements several hundred feet in the air is orders of magnitude greater than it is on the ground. The oxygen concentration is lower, the wind speeds are greater, and the sun is dazzling. The only organisms able to live at such heights are birds of prey. While it is true that the trees are being selected for their hardiness and receive botanical care, I predict they will neither grow very much, nor survive long. This is not the way to increase green spaces in cities.

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The ‘supertrees’ of Singapore do not suffer as many of the flaws as the vertical forests of Milan, although they too struggle to counterbalance the carbon dioxide released into the atmosphere in producing their giant concrete trunks. With their great swathes of solar panels, they are more likely to have a net positive effect in terms of atmospheric levels of greenhouse gases. They also collect rainwater and act as air venting ducts for nearby conservatories. Yet, costing millions to construct and taking up valuable space within the city, they are not a realistic solution to the problems of modern cities. Admittedly they are a great tourist attraction and spectacle, increasing awareness of environmental problems, but the solutions to these problems lie elsewhere.

These two projects have the right intention but the wrong execution. The large-scale return of life to our cities by creating alternative environments and niches is an unrealistic goal.  Instead we should reduce the environmental impact of cities. Reducing waste or exploiting it for other uses, reducing the air, noise, and light pollution of our cities, and preventing further expansion are better and more achievable goals, helping to protect the wildlife which still exists outside our cities. Rather than attempting to improve what has already been destroyed, we should strive to preserve what nature we have left.