Deconstructing... vertical forests

"Vertical forests do work, but they need to be more than just window dressing"

Jock Gammon, Co-founder, Junglefy, Sydney

One of the main arguments against vertical forests is that they're greenwash, just there for marketing purposes. Our view is that all living infrastructure needs to have a function beyond just looking beautiful.

At One Central Park Sydney – our first big project – all the gardens are irrigated by recycled blackwater from an on-site treatment centre, and sewage is used to fertilise the gardens. Greenery can alsoreduce a building's heat output by 25-30%: that means huge long-term energy savings.

The main driver for what we do is to make our cities happier and healthier for people, by installing green walls using plants that can actually clean the air, for example. These walls may only remove the pollution produced by a small number of cars – but ask yourself what benefits are there in not having them in our cities?

I think we lost touch with nature somewhere along the way. Now, there's a huge groundswell of people realising that.

"Practical considerations might limit their widespread take-up"

Daniel Safarik, Editor, Council on Tall Buildings and Urban Habitat, Chicago

People tend to get very excited about a few examples of vertical forests, which tells you it's still fairly early days for them. Do we expect to see most buildings covered in vegetation in five years? Probably not.

I don't think you could argue these types of buildings are net positive in terms of removing carbon from the air – think about how much concrete is required for a facade to be able carry the weight of full-sized trees. And how do you control access to people's private property so that the facade can be maintained? Someone is going to have to either come through your apartment at some point, or rappel down the building to do some trimming.

But, if you have an obligation to densify population levels in cities, the aesthetic benefits of vertical forests might help persuade people resistant to the idea of high-rise living to give it a go. And adding vegetation to surfaces that aren't porous, reject water and reflect light can help to keep a lid on the urban heat island effect.

"In isolation, the environmental benefits are minimal, so we need to build more"

Todd Gartner, Director, Natural Infrastructure Initiative, World Resources Institute, Portland

Urban centres are a key component in our planet's biodiversity, not just for animals that live in cities, but also for migrating birds whose journeys have become increasingly difficult as urbanisation and sprawl chips away at their natural stopping points.
Vertical forests are by no means a silver bullet, but they do still offer great benefits, as you create more green spaces in cities green building is going to make that big a difference. But in aggregate, this approach could be critically important.

"Even if their impact is more symbolic than scientific, every little helps"

Rob Mackenzie, Professor of atmospheric science, University of Birmingham

Planting trees and bushes around a tall building can only ever have a small effect on air quality. There's very little time for pollutants to be deposited on to the branches and the leaves because air passes a building quite quickly. It'd be a very roundabout way of trying to fix air pollution.

That's not to say there aren't other benefits. In principle, one could get some quite strong microclimate effects from really radically greening a city, so the vertical forest could help a bit with that. And certainly the more surface area there is transpiring water out into the atmosphere rather than absorbing heat and releasing

it at night – the urban heat island effect – the better. There are also good arguments around biodiversity – although not everybody appreciates the birds, bugs and bats that are what biodiversity really means.

But by far their biggest impact will be made through hearts and minds, by being a beacon and providing a vision of what we can do in terms of marrying tech and nature.

• This article originally appeared in the March 2019 edition of Modus