Box 9.1: Green cities – four short stories

Detroit's imposing Art Nouveau railway station, closed since 1988, may become a 16 storey, stacked market garden, growing vegetables and salad for the local farmers’ market. In an urban food desert, food growing makes sense. All the hype about Detroit's decline overlooks the promise and potential of a green and liveable city. Around 300 green, open spaces replace what were once well laid-out, built-up streets. Many have become urban farms. Urban agriculture and tree planting are one of Detroit's new enterprises. So is land reclamation for environmental and ecological reasons.

Industrial cities remind us not of woodland, but of smoke stacks and ‘satanic mills’. Yet Sheffield, the archetypal industrial city in England's northern manufacturing heartland, a pioneer in the industrial revolution, sometimes called England’s ugliest city, has 2 million urban trees, more per citizen than any other city in Europe. Sheffield borders the Peak District National Park, where, before its creation in the 1930s, workers from Sheffield, Manchester and other industrial cities invaded the protected moorland in a mass trespass to open up the grouse shooter's private land to city dwellers, and changing for posterity the way a shrinking natural environment is shared.

The city has 170 woodlands within its borders, 80 of them ancient, dating from long before Sheffield's urban-industrial explosion. Its early 19th century botanical gardens and its 21st century, glass-covered Winter Garden, with 2500 trees, shrubs and flowers from around the world, show the value of green, shared spaces within cities. They make cities cleaner, quieter, cooler and they absorb CO2, helping to combat climate change. Seven public parks are packed within this dense city, built on seven hills. Today, Sheffield's residents are fighting in the terraced and semi-detached city streets to stop private contractors chopping down mature trees, which lock up thousands of tonnes of carbon, on the basis that mature trees are more expensive to maintain.