PARIS • From lettuces farmed on New York's skyline to corridors of trees occupying once desolate Colombian roadsides, green initiatives are running wild in cities around the world.
At a time when coronavirus lockdowns have amplified the need for nature in urban areas, images and footage reveal projects optimising precious city space.
Replanting initiatives have sprouted up since the start of the 21st century as urban development goals have shifted and alarm about global warming has grown.
In cities, thanks to planting schemes on walls and roofs, the temperature during the warmest month in street canyons - flanked by high-rise buildings on either side - can be reduced by 3.6 deg C to 11.3 deg C at the hottest time of day, according to the French Agency for Ecological Transition.
Green spaces have also been shown to improve health and well-being, including by reducing stress, anxiety and depression, improving attention and focus, promoting better physical health and help in managing post-traumatic stress disorder, said Dr Stephanie Merchant of Bath University's department for health. "However, it's about where they are created in relation to the needs of the local communities."
So are all urban replanting projects worthwhile?
For a scheme to be seen as "virtuous", it must fulfil as many functions as possible, said economist and urban planner Jean Haentjens.
In addition to lowering the temperature, he said it should also preserve biodiversity, improve well-being, raise awareness and be appealing to residents.
In Singapore, an imposing "forest" of giant man-made trees constructed from reinforced concrete and steel, luxuriantly covered in real flora and fauna, is a landmark.
Towering 25m to 50m over the city-state's business district, the 18 solar-powered supertrees light up the night sky, their canopies looking like flying saucers. Vast glass greenhouses showcase exotic plants from five continents, as well as plant life from tropical highlands up to 2,000m above sea level, complete with an artificial mountain and indoor waterfall.
The Gardens by the Bay project, awarded the World Building of the Year in 2012, says the idea was to create "a city in a garden".
But pointing to the construction and maintenance costs, Mr Philippe Simay, a philosopher on cities and architecture, called it a "disneyisation" of nature. "Why make trees from concrete when you can have real ones?" he asked.
It is a great public relations effort, said Professor Claire Doussard, a teacher in planning and development and a research fellow at the French National Centre for Scientific Research, highlighting its "technical know-how" and awareness-raising among the public about the threat of climate change.
In New York, with buildings all around, the Statue of Liberty in the distance and heavy traffic below, the Brooklyn Grange rooftop farm grows more than 45 tonnes of organic produce a year. It was launched about a decade ago by friends living in the city who wanted "a small sustainable farm that operated as a business", co-founder Gwen Schantz said.
In a built-up city, Mr Simay said, it has been found that such initiatives were "fighting effectively against heat islands" where heat-conducting concrete and asphalt make cities warmer than their surroundings. Now covering three rooftops, totalling more than 22,000 sq m, the farm cultivates a wide variety of vegetables.
Prof Doussard said the logistics of rooftop farming, where water and soil must be hauled up and produce brought down, means "these farms must be profitable because there are a lot of constraints".