Shifting from grass to trees would reduce emissions and increase biodiversity, experts say.
Dig up your “imperial” lawn and replant it with trees to combat the climate crisis, researchers have urged, after the latest study to lay bare the emissions cost of maintaining that pleasant, green patch.
If a third of the world’s city lawns were planted with trees, more than a gigatonne of carbon could be removed from the atmosphere over two decades, researchers from Auckland University of Technology found. The problem is not the grass itself, but the mowing, fertilisation and irrigation required.
The researchers reviewed 65 studies of emissions and sequestration of carbon by turf or lawn compared with trees. They concluded that, globally, the equivalent of 157 tonnes of carbon dioxide emissions per hectare could be avoided, and up to 1,630m tonnes of carbon absorbed from the atmosphere over 20 years if a third of mown grass in cities were planted with trees.
The traditional lawn – a uniform, trimmed carpet of ryegrass – has been under fire for years because of its lack of biodiversity and voracious appetite for fertiliser, herbicides and mowing.
As climate breakdown drives more extreme weather, droughts have highlighted the irrigation demands of velvety turf. In response, anti-lawn and “rewilding” movements have seeded across the UK, with advocates pushing to replace the lawn with trees, shrubs or a more diverse mixture of unmown wildflowers and native grasses. In 2021, 30 UK councils adopted “No mow May” to encourage wildflower growth and natural pollinators.
The research’s lead author, Prof Len Gillman, said that while abandoning the mower and letting a lawn go wild “might cut down on the emissions due to maintenance, it’s not going far enough”.
“In terms of climate change we need to absorb as much carbon as we possibly can from the atmosphere …. The biggest difference is that shrubs and trees will store vastly more carbon than a lawn.”
In countries such as Australia, New Zealand and the US, the lawn represented a throwback to the colonial era, Gillman said, when lawns were strongly associated with affluence and nostalgia for English landscapes. Now, “a lot of lawns almost happen by mistake, as a default setting”, he said.
Expanding urban forests and tree numbers had other benefits too, Gillman said. Trees could cool the atmosphere in increasingly overheated cities, and were associated with benefits to health and wellbeing.
Previous studies have found that lawns occupy 50-70% of the green open spaces in the world’s cities, and almost 2% of the total area of the US.
The research was published in the January 2023 journal of Global Sustainability by Cambridge University Press.
