Urban ecosystems are of growing importance. Until quite recently the world population
was mainly non-urban; now, after rapid urbanisation since the 1800s, over 50 per
cent of people live in cities, and the percentage is increasing. Many of the largest, fastest
growing cities are in poor countries and pose severe environmental problems. Urban
ecosystems have far-reaching ‘roots’ drawing inputs from a huge catchment; cities also
influence decision making that affects rural areas, discharge polluted effluent, contaminate
the air flowing past, and generate huge amounts of refuse. Even in developed
countries urban environments are a challenge for environmental management (see
Chapter 15). In recent years there has been a shift in interest from just coping with city problems to seeking strategies for ‘sustainable cities’ – however, there is a long way to
go before there are practical solutions. Engineering and institutional developments alone
will not provide solutions for urban transport, water supply, sanitation, control of crime,
or improving social cohesion. For effective environmental management there must be
a better understanding of urban and peri-urban environments, societies and economies,
and how they interact with rural surroundings.