Nature in an Urban World

Looking at the skyline, it is hard for me to imagine that just a few decades ago this was a sleepy town by the Fustian River. The skyscrapers of Shenzhen now stretch out to the horizon. Some of the newer towers have a glass façade and fashionable design, but many of the other buildings appear as more or less identical grey concrete blocks, lined up in long rows that shrink toward the horizon. And then everywhere, ubiquitous, are the cranes. The cranes of Shenzhen are always moving, flitting from one building site to another, frantically assembling steel beams into the frames for new skyscrapers. In a few short decades, they have built a city where once there was a small village, and they keep on building. Farmers' fields have disappeared under a forest of skyscrapers, in just one generation. How did this dramatic urban growth happen?

Every city's story, like every individual's life, is unique and full of happenstance. For many decades, the Chinese government under Mao Zedong actively tried to keep cities from growing and in some cases forced urban youth to move to the countryside. With Mao's death and new political leadership, this anti-urban attitude eased a little bit. Shenzhen, then a small town of just 60,000 people (UNPD 2011), was designated one of China's four Special Economic Zones (SEZs), where free market policies and urban development were allowed. All of the suppressed economic development of China began to concentrate in these SEZs.

Shenzhen's location, just across the river from the bustling city of Hong Kong, was perfect. It had a large, deepwater port and, compared with Hong Kong, cheap wages. Manufacturers rapidly set up factories, and during the 1980s the industrial output of the city grew by 60 percent a year (Montgomery et al. 2003). The total population surpassed 10 million in 2010 (UNPD 2011), an astonishing 175-fold increase in its population since becoming an SEZ.

But the dark side of such rapid growth is severe environmental challenges that affect residents' quality of life. Shenzhen's water supply system has struggled to keep pace with its burgeoning population, and providing water of sufficient quality has required significant new infrastructure. Shenzhen's air quality has declined, as industrial production and millions of cars on the road have led to high levels of smog and particulate matter (Che et al. 2011). The rain is so acidic, due to sulfur dioxide and nitrogen oxide from coal-burning power plants, that it sometimes damages the paint on cars. Shenzhen has the distinction of having one of the fastest urban growth rates in the world (UNPD 2011). But while extreme, its story contains themes that are present in many urban areas. Many other cities in both the developing and developed world are experiencing growth (fig. 1.1), and are struggling to accommodate that growth while protecting the environment. All this growth will require new infrastructure, as will the challenge of adapting cities to climate change.

The twenty-first century will be the fastest period of urban growth in human history. In a few decades, more homes will be built than have accumulated over centuries of urban development in Europe. Rapidly urbanizing regions like Asia and Africa will add billions of people to their cities (fig. 1.1). In a sense, Asia and Africa are catching up with Europe and the United States, which already have substantial proportions of their total populations living in cities. Even in developed countries, however, urban population often continues to expand in some urban areas, driven by overall population growth or shifts in population among cities. Older infrastructure in growing cities needs to be refurbished or replaced. Globally, the twenty-first century will require massive urban infrastructure development, in roads and pipes and power lines and schools.

Ecologists, urban planners, economists, and landscape architects are increasingly asked to consider the role that natural infrastructure — the natural habitat or constructed natural spaces that supply crucial benefits to urban residents — can play in meeting these challenges. Whether it is the role of upstream forests in maintaining water quality in reservoirs, how shade trees keep cities cool during heat waves, or the way parks can contribute to the quality of life and financial success of a city, natural infrastructure is all the rage.

Even in Shenzhen, the concept of natural infrastructure has caught on. By 2000, the city's rapid urban growth had made the Fustian River an open sewer. The river had been channelized, with concrete embankments boxing in the its foul waters for most of its length as it passed through the city. In 2009, the Shenzhen Fustian River project began. At a cost of 300 million yuan (US$49 million), the project first created new pipes to carry stormwater and sewage water to a treatment facility, to limit the release of untreated sewage into the Fustian. But this grey infrastructure investment — concrete and pipes and other engineered structures — was complemented by an investment in green infrastructure. The concrete embankments were torn down, replaced by sand and mud and pebbles. Eventually, artificial wetlands were created in low-lying areas of the floodplain, to further filter stormwater as it reached the Fustian, as well as to provide a beautiful park along the river (Lide 2013).

Yet for all the excitement about natural infrastructure, guidance on how to plan and implement projects is often hard to come by. How can a city like Shenzhen tell which of nature's benefits — the ecosystem services provided by natural habitat — are most important? How can they map which patches of natural habitat are most important, and quantify the economic benefits they provide? How could planners in the Shenzhen Water Planning and Design Institute, which ran the Shenzhen Fustian River project, find the optimal mix of natural infrastructure and traditional grey infrastructure to solve problems facing a city? Perhaps most important, what are the regulatory and policy tools that a city like Shenzhen can use to help fund and implement natural infrastructure projects?

Conservation for an Urban World

Cities need nature to survive and thrive. And yet the traditional viewpoint of environmentalists concerned with "nature" has been that cities are the enemy. It is true that as cities have expanded, they have affected a lot of biodiversity. One-third of all imperiled species in the United States are in metropolitan regions (NWF, Smart Growth America, and NatureServe 2005), and globally at least one in ten vertebrates is impacted by urbanization (McDonald, Kareiva, and Forman 2008). Conservation planners, wildlife managers, and other practitioners who focus...