Urban ecology , simply put, is the study of life in the city. In the late nineteenth century, biologists and zoologists created the field of ecology, seeking to understand the complex relationships between organisms and their environment . The term ecosystem started to be used to refer to a community of organisms and its associated environment when functioning as an ecological unit. Since then, the study of ecosystems has largely been associated with scientific descriptions of pristine locales, typically in remote regions where human presence was minimal to non-existent. In contrast, urban ecology is the study of urban ecosystems. In general, urban biodiversity is heavily dominated by alien species . There are exceptions, for instance suburban communities that retain parts of the pre-existing natural habitat , but overall, urban ecosystems are fundamentally anthropogenic , meaning that they are man-made.
Evidence of human action on the environment goes back thousands of years. Human hunters in North America played a role in the extinction of large mammals as far back as 12,000–5,000 years ago. The development of agricultural societies led to side effects including soil erosion , disease, and deforestation before modern times. In some ancient cities, ecological degradation was severe, and ruined cities and cultures have left behind ample evidence for modern day researchers. Over thousands of years, humanity has played a major role in changing the ecosystems in which they have lived, and in modern times this process has become prolific and widespread.
In the new millenium, ecologists have little doubt that humanity's collective will is the dominant force in the welfare and outcome of the global environment. With nearly half of the world's population living in urban areas, and almost 80% of people in developed nations living in cities, mankind consumes a vast amount of resources, most of which comes from ecosystems outside the city. Large amounts of renewable and non-renewable resources are being transported from outlying ecosystems into urban ecosystems, while huge quantities of human produced pollutants are being created by urban ecosystems and spread across the spectrum of ecosystems. For this reason, urban ecologists stress the importance of understanding, in ecological terms, how the activities of people affect the total ecological spectrum from pristine wilderness to urban areas.
Ecologists define an urban ecosystem as a dependent ecosystem, meaning that it depends on other ecosystems and outside energy and resources to function. On the other hand, a natural ecosystem generally has an even balance between its energetic inputs and outputs. William Rees, a researcher at the University of British Columbia, created an analytical tool to measure just how dependent the urban ecosystem is. Called the "ecological footprint," it roughly measures how much land is required to maintain a city's activities. Rees found that Vancouver, British Columbia, for instance, had a footprint 180 times its own size in 1996, meaning that much more land, in terms of extractable resources, is required to support its inhabitants.
Another aspect of the urban process being studied is the urban fringe. The fringe is the expansion point where human activity, building, and structure meet and alter other existing ecological or natural settings. Also known as urban sprawl , this process, according to Bioscience magazine, chewed up an estimated 13 million acres (5.3 million ha) of land in the United States between 1970 and 1980, and another 9 million acres (3.6 million ha) in the 1980's. Additionally, development of farmland and forest during the economically booming 1990's reached a record pace in America, accelerating to a rate of 3.2 million acres (1.3 million ha) per year by some estimates.
This rapid development has profoundly changed the ecosystems involved and a thriving branch of urban ecology studies how patterns of urban development alter the ecological composition and organization of species. For example, the change in predator and prey relationships caused by human activity has altered the wildlife population in several habitats. Some animals have become more familiar and comfortable with the urban environment, and human-to-animal encounters have increased. Deer have been seen walking casually through suburban neighborhoods across the United States, feeding on saplings and freshly planted gardens, and traffic incidents involving them have increased. In Washington, D.C. deer have been seen a short distance from the White House. A coyote was found in an elevator in a Seattle federal building. Many coyote, whose numbers have doubled since 1850, have been frequently sighted looking for food in suburbs and urban areas. Another result of human interference with natural habitats is the changing predation habits among certain animals. For example, in California, foxes have begun killing rare bird species. Concern among environmentalists and ecologists continues to grow as the phenomenon of urban growth and development increases. Other fields of study include the mechanisms of carbon storage in the urban forest and cooling of the atmosphere by urban evapotranspiration .
Scientists understand that traditional ecological theory, developed without humans in mind, is not sufficient for properly understanding urban systems. Instead of considering humans as being outside or separate from the natural world, ecologists include humans as a factor affecting the natural world's evolution . Together with an existent natural landscape, the forces of human policies and economics have the greatest impact in how an urban ecosystem is created and maintained, as well as how plant and wildlife fare. When looking at cities, ecologists might include data such as species diversity, population sizes, and energy flow . Urban ecologists would further include qualities having to do with human perceptions and institutions, including cultural resources, educational opportunities, recreation , wealth, city design and aesthetics, and community health. Features of the urban ecosytem include, for instance, money (a property of energy in the urban ecosystem), downtown high-rises, social institutions, industrial developments, commercial shopping developments, residential developments of all cultural and economic types, open space and recreational parks, automobile traffic, pedestrian traffic, air pollution and toxic contaminants, existing natural landforms, and adaptive plants and wildlife. The large number of factors influencing the urban environment shows the need for the inclusion of other sciences in order to understand the urban area's complexity.
In the United States, the National Science Foundation's Long-Term Ecological Research (LTER) project has the goal of creating a full-scale, interdisciplinary urban ecology research program that addresses the field's complex needs. The project, begun in the 1990's, is using two sites for research, in Phoenix, Arizona and Baltimore, Maryland. Interdisciplinary teams of the project's scientists are working to better understand the urban environment. This study provides an example of how an urban ecology analysis is conducted. First, researchers focus on the urban topography , and more precisely analyze a watershed (defined as an area that is being drained, or feeding a body of water) as a centerpoint. Scientists then begin to link up the ecological relationships of vegetation and wildlife communities. After examining the ecological relationships, the next step is to understand the human socio-cultural characteristics of the watershed. Different areas along watersheds have different land values. Urban ecologists study the relationship between the natural features of the watershed and how humans interact, according to different sociological characteristics such as age, gender, ethnic identity, and social status. Significant patterns can often be seen between social factors and a particular urban area's biophysical (natural) characteristics. For instance, studies have found that wealthy city dwellers tend to live in areas that are environmentally healthier and less polluted than those lived in by poorer city dwellers. The LTER project is comprehensively addressing issues like this, using a variety of scientific methods.
The science of urban ecology is also part of a growing awareness that the health of the overall environment depends upon the health of cities. In addition to the scientific study of ecology, this awareness is also associated with the more activist areas of "ecological urbanism" and "new urbanism," as well as "green living" and "sustainable development" trends in urban planning. The aims of ecological urbanism and new urbanism are to create justice and equity in social and environmental policy . These movements also strive to reform urban landscapes and urban planning methods to create sustainable, healthy cities by reducing pollutants and waste, while increasing conservation and the accessibility of shared resources, to insure humanity's survival and quality of life. Urban ecology contributes the resources of knowledge and information to these social movements, and to those who seek a deeper understanding of the relationship between humanity and the natural world, helping them see their city as part of a living ecosystem with valuable resources that promote better health and quality of life.
[Douglas Dupler ]
Beatley, Timothy, and Kristy Manning. The Ecology of Place: Planning for Environment, Economy, and Community. Washington, DC: Island Press, 1997.
Breuste, Jurgen, Hildegard Feldman, and Ogarit Uhlman. Urban Ecology. Berlin, New York: Springer-Verlag, 1998.
Matthews, Anne. Wild Nights: Nature Returns to the City. New York: North Point Press, 2001.
Rocky Mountain Institute. Green Development: Integrating Ecology and Real Estate. New York: John Wiley & Sons, 1998.
The Baltimore Ecosystem Project. [cited July 2002]. <http://www.ecostudies.org/bes>.
The Center for Urban Ecology, 4598 MacArthur Blvd., NW., Washington, DC USA 20007-4227 202-342-1443, Fax: 202-282-1031, <http://www.nps.gov/cue/cueintro.html>