Giving nature free rein in cities could help to reduce the threat of floods and heatwaves, improve people’s well-being and conserve wildlife, according to a report from a British charity.
Rewilding could be used to tackle climate and nature crises in a “low-cost, hands-off way”, researchers at the Zoological Society of London (ZSL) said.
The policy could also improve people’s health, but it must be carried out carefully and with the support of communities, to reduce the risk of invasive species and avoid conflicts between people and wildlife.
The practice is usually associated with the countryside, where farmland is left to return to scrub, or woodland and grassland is grazed by livestock.
Beavers have been reintroduced to some cities in the UK to restore wildlife-rich wetlands through building dams and felling trees, and slowing, storing and filtering water, which attracts other wildlife to those habitats and reduces flooding downstream.
There are opportunities for giving nature freer rein across cities, the report said.
Examples could include less management and wilder areas in parks, cemeteries and along railway lines, and letting nature take over abandoned industrial sites.
Rivers could be taken out of the culverts they have been buried in or allowed to become lined with vegetation, while fish barriers could be removed.
Residents can leave part of their gardens wild and avoid laying artificial lawns and pesticides.
About two-thirds of the world's population are expected to live in cities by 2050.
Climate change is increasing the risk of heatwaves, which are made worse by the heat that becomes trapped by buildings and paved areas, and flash floods from more heavy rain.
More diverse greenery and space for water, which cools the air, absorbs rainfall, cuts air pollution and provides habitat for wildlife, should be encouraged, researchers said.
Greenery can reunite people with nature, improve health and well-being and strengthen local economies as they attract visitors to wildlife and enjoy the outdoors, the report said.
The study points to ZSL's work in its car park at London Zoo, where the mowing of the grass was stopped, trees were seeded or coppiced for zoo animal feed, and bramble thickets were managed to provide nesting sites for the hedgehogs that now thrive there.
It also raised the possibility of reintroducing species such as Eurasian beavers.
Beavers have started to return to urban areas in the UK, such as the northern edge of London, where the “ecosystem engineers” have been reintroduced by Enfield Council and Capel Manor College into a woodland enclosure.
It is hoped their building dams and creating localised wetlands will boost wildlife and reduce flooding in urban areas when climate change brings more heavy rain to the British capital.
“Wildfires, floods and heatwaves across the world have brought the climate crisis to the fore for many people this year,” said Dr Nathalie Pettorelli, lead report author and climate and biodiversity expert at ZSL's Institute of Zoology.
“The interconnection of the climate crisis with the loss of nature is thankfully now widely recognised, and rewilding is an approach being increasingly embraced.
“However, the large-scale rewilding of urban spaces, including creating nature corridors and wild spaces around city infrastructure, is something that has so far been relatively overlooked as part of the solution.”
Giving nature freer rein across cities could not only help to buffer them against extreme climatic events such as storms, floods and heatwaves by helping to cool them and create natural flood defences, but also help boost urban wildlife by habitat creation, she said.
Dr Pettorelli said expert guidance was needed as “well-meaning but misguided” attempts could harm wildlife and threaten public health through the introduction of invasive species.
Some people may see wilder areas in parks as unkept or attracting fly-tipping, while “green gentrification” — where improving the natural environment in a city area can increase investment and property prices could push disadvantaged people out, the report said.
