The walled cities of the ancient and medieval worlds had little public space with plants, because the land protected by their walls was so valuable. From the sixteenth century to the twentieth century European cities became progressively more vegetated. This process can and should accelerate in the 21st century. We have the technology to vegetate most roofs and walls; we need more plants to absorb CO2; we need more biodiversity; we love greenery in cities. Cities are habitats for plants and animals – as well as humans.
London is famous for using a higher percentage of its land for parks and gardens than other cities of its size. Part of the reason is historical. Protection by surrounding seas let London dispense with walls at an earlier date than other European capitals. Another reason may be Britain’s climate. It is rarely too cold and rarely too hot for the enjoyment of outdoor leisure activities.