Cities, which already host half the world’s population, are predicted to absorb nearly all of the growth of population over the next three decades. The concentration of humanity in relatively small spaces brings with it enormous environmental challenges, particularly in the low-income and middle-income countries. Among many factors that influence the quality of the urban environment, biodiversity is arguably the least appreciated. It is welcome, therefore, that the key role played by biodiversity in providing a host of ecosystem services to people is being emphasised during 2010, declared as the International Year of Biodiversity by the United Nations General Assembly. In the cities, green areas reduce pollution and improve the quality of air; wetlands break down waste and recycle it; and parks and woodlands with their colourful flora and fauna help city-dwellers connect with nature in their backyard. City governments must reflect on the ways in which the negative impact of urbanisation on biodiversity can be minimised, and biodiversity enhanced. As conurbations and megacities grow, nature-provided commons such as air, water, and green areas need to be zealously protected. Cities occupy less than three per cent of the world’s land surface and their activities can be regulated. On the other hand, the number of cities with a population of over a million is increasing rapidly, leaving a disproportionately large ecological footprint on natural resources extracted from elsewhere.
It is interesting that several cities, including Curitiba, Nagoya, Brussels, and Paris, are testing a new framework to assess the health of their urban biodiversity. This tool, the Singapore Index on Cities’ Biodiversity created under the Convention on Biological Diversity of the United Nations Environment Programme, should be of great interest to India. The index, which has some core indicators such as birds, butterflies, and plants, and a broader range of optional indicators, including mammals, can lead to a good assessment of the stressors that are depleting cities of biodiversity (such as unregulated building, loss of green areas, and wetlands), and thus affecting ecosystem services. Many cities in developing countries, particularly those in the tropics, can benefit from an honest appraisal of the biodiversity they retain. Such data are vital, because research shows that compensatory efforts to replace lost ecology are inferior in biodiversity terms. Artificial wetlands, for instance, cannot maintain the same level of ecological function as natural ones as they lack the full range of life forms. Cities stand greatly to benefit from enhanced biodiversity, and mayors and governments must factor that into their development plans.