A study published in Nature estimates that there are 3.04 trillion trees worldwide. That means there are about 422 trees for every person on earth. The study also shows that the total number of trees has decreased by about 46 percent since the dawn of human civilization. This decline is particularly evident in urban settings, where we have positioned ourselves as homo urbanus, seemingly above and beyond nature. However, this trend has started to shift as urban ecologists, planners, residents and city councilors are adopting ecosystem-based approaches to enhancing local biodiversity, ranging from planting trees to creating urban gardens.
For example, the Unesco headquarters in Paris recently transformed its historic garden, steeped in works by Henri Moore, Takis Vassilakis and others, into a “jardin potager” – an edible landscape with over 140 species of aromatic and medicinal herbs, vegetables and fruit trees. The aim is to bring culture back to farming, provide seasonal inspiration to in-house chefs and provide a space for international officials to nourish body and mind.
When it comes to the question of how many trees there should be for each person in urban areas, I like the thesis proposed by Dutch ecologist Cecil Konijnendijk, enshrined in the “3-30-300 rule”. This stipulates that everyone can see at least three trees from their house; each neighborhood should have 30 percent canopy cover; and 300 meters should be the maximum distance to the nearest quality public green space.
In New York, forest cover has increased an estimated 20 percent since 2016, offering New Yorkers an escape from the concrete jungle and helping cool the city. A new initiative, following Million Trees NYC, aims to plant an additional million trees in five boroughs. For years I supported a similarly ambitious urban greening project to transform Vila Brasilândia, believed to be South America’s largest slum, into a 20-minute neighborhood. Her campaign, The Forest Invades the City, aimed to reverse the trend of predatory human occupation of São Paulo’s green belt by planting native trees, installing green roofs and growing edible plants in abandoned public spaces.
Another recent example can be found in Madrid, where a green wall is to be erected around the city in the form of a 75-kilometer urban forest, where almost 500,000 new trees will be planted to improve air quality and lower temperatures. When planted and matured, it is expected to absorb 175,000 tons of greenhouse gas emissions each year and combine with the surrounding forests.
In recent walking interviews I conducted in Edinburgh, women in Portobello closer to me told me of their desire to help design natural corridors, combining parks and playfulness with forests, orchards and fires with the larger landscape of sea and hills . Brunstane Burn has been proposed as a route running from Arthur’s Seat to the sea, with one woman describing it as “a broken corridor, but if ecologically and socially connected it could be brilliant”. In fact, Brunstane Burn is “a huge asset that the other parks could decouple from.”
From a leafy neighborhood in Edinburgh to a slum in São Paulo, from UNESCO to Manhattan, many are beginning to awaken to the biocentric fact that we are one of the many species in the co-evolving web of life. By restoring the existing connections between individual trees, urban forests, green spaces, fires, allotments, and the soil beneath vegetation, we can help our cities reduce greenhouse gas emissions, contain extreme heat, bring back biodiversity, and enrich our urban lives.
May East, UN House of Representatives Urban Program Coordinator for Scotland