Urban Ecosystems 5: In Defense of Cities

What You Need

Urban Ecosystems 5: In Defense of Cities Photo Credit: Science NetLinks


To understand that while cities have unattractive features, the density of human life enables energy efficiency, mass transit, recycling, and other benefits which are difficult or impossible in rural areas. Thus, the impact of any given individual urban dweller on the environment may be less than that of a suburban or rural individual, while quality of life may by some measures be higher.


This lesson was developed by Dr. Penny Firth, a scientist, as part of a set of interdisciplinary Science NetLinks lessons aimed at improved understanding of environmental phenomena and events. Some of the lessons integrate topics that cross biological, ecological, and physical concepts. Others involve elements of economics, history, anthropology, and art. Each lesson is framed by plain-language background information for the teacher, and includes a selection of instructional tips and activities in the boxes.

This is the fifth of a strand of five lessons entitled Urban Ecosystems: Continuity and Change:

  • Urban Ecosystems 1: Cities are Urban Ecosystems
  • Urban Ecosystems 2: Why are there Cities? A Historical Perspective
  • Urban Ecosystems 3: Cities as Population Centers
  • Urban Ecosystems 4: Metabolism of Urban Ecosystems
  • Urban Ecosystems 5: In Defense of Cities

This lesson series addresses the concept of cities as urban ecosystems that include both nature and humans in a largely human-built environment. Students will be shown the importance of food surpluses to the historical development of urban ecosystems. They will also learn how the exploitation of forests, irrigation waters, and other resources led to catastrophe for some early cities. One lesson shows that the size and number of modern urban ecosystems is unprecedented and that fossil fuel use is a key factor in this. Material and energy flowpaths into and out of cities will be described and students will have the chance to consider how and where these flowpaths are linear versus cyclic. Finally, students will look at some of the positive environmental features of urban ecosystems.

Cities get trashed a lot, for some good reasons. Cities have tended to concentrate pollutants. They are noisy, crowded, and have problems with crime and transportation. But when you consider the alternatives, cities suddenly do not look so bad. What if all 6.2 billion people on the planet were spread out across the landscape? How would that influence the cleanliness of our waters and air? The biological diversity of our wild areas? Would there even be any wild areas left? Cities, for all of their warts, allow humans many kinds of opportunities: economic, political, cultural, artistic, social, and even environmental.

Many of the problems with cities in the United States have been exacerbated by post World War II development patterns. Planning and building became centered around the automobile, with the assumption that this would increase personal freedom and quality of life. Unfortunately, what happened in many cases was that single-use enclaves resulted that required people to get in their cars in order to move around. Housing for similar income levels was grouped together, often in huge suburban tracts. Retail stores were clustered into large malls, or strung out in strip shopping centers along busy thoroughfares. Businesses were often grouped into business parks or industrial parks accessible mainly by car. These kinds of development patterns have actually limited options for walking, biking, or mass transit and contributed to the problem of sprawl in many cities and suburbs.

In addition to environmental problems associated with sprawl, there are serious quality-of-life issues. People may feel separated and isolated from one another, a sense of community is difficult to achieve, and folks spend way too much time stuck in traffic. In contrast, a thoughtfully-designed city can offer superior quality-of-life for residents and may also minimize environmental impacts of the people living there and give the inhabitants a sense of being closer to nature. Even simple connections such as bird feeders and community gardens can contribute to a sense of well-being in an urban area.

A common student misconception related to this topic is that city-dwellers are inevitably greater consumers of energy and materials, and producers of waste, than suburbanites or people who live in rural areas. On a per capita basis, this may not always be the case. This lesson will demonstrate to students how everyday choices in lifestyle affect their impact on the environment and how these might vary from city to suburb to rural living.

The density of human life in cities makes for energy efficiency in home heating as well as in transportation. Waste disposal and recycling services are more easily organized in densely inhabited areas, and protection of air and water can be facilitated where the problems are concentrated in one political jurisdiction.

In Urban Ecosystems 5, the class will learn about the concept of an ecological footprint. They will use an online ecological footprint calculator to compare the environmental impact of different levels of resource use, kinds of transportation, and similar factors. The second exercise will explore the natural world that exists in their community, no matter how urban it might be. Finally, they will brainstorm the qualities and characteristics of what they might consider an excellent, livable community.

Dr. Firth would like to gratefully acknowledge Drs. Morgan Grove (U.S. Forest Service), Alan Berkowitz (Institute for Ecosystem Studies), and Matt Klingle (Bowdoin College) for reviewing the Urban Ecosystems: Continuity and Change set of Science NetLinks lessons and providing valuable comments and suggestions.

Contact Dr. Firth at pfirth@nsf.gov.

Planning Ahead

You should visit the Ecological Footprint Quiz before taking your class there, just to get an idea of some of the questions on the site and to be ready with responses if your students do not know the answers to some of them.

Note: If this happens, you might choose to use the default response for the average American that the designers of the website have indicated.

If possible, get a copy of the Bruce Springsteen song, My Hometown, to play in class:


Motivate this lesson with a brainstorming session about the activities that tend to bring people together. These might include: employment, education, recreation, entertainment, shopping, and services (e.g. orthodontist, appliance repair).

Ask students how the people in their family get to these activities (i.e. walking, bicycling, mass transit, cars, boats). If the most common form of transportation is car, explore with the class some alternative ways of getting around. What might be the benefits of these? The problems?


Ecological Footprints
The ecological footprint is a mental tool created by William Rees and Mathis Wackernagel that is a simplistic way of measuring certain human impacts on nature. It shows how much productive land and water humans use to produce all the resources we consume and to take in all the waste we make. The average American uses 24 acres to support his or her current lifestyle. In comparison, the average Canadian lives on a footprint 30 percent less, and the average Italian on 60 percent less.

Calculating Ecological Footprints
Take your class to the Ecological Footprint Quiz. Answer the questionnaire to calculate an Ecological Footprint for an individual living in the United States.

You can use an actual person (e.g. yourself) or make up answers with your class for a hypothetical individual. There are 13 questions divided into three sections (food, transportation, and housing). The default answers represent North American averages. Note: There is no math involved. The authors have done the math behind-the-scenes and you simply answer the multiple-choice questions.

Explore how the ecological footprint of a person might differ depending upon where he/she lives (urban, suburban, rural). To do this, try using different modes of transportation and housing, as well as food, in answering the questionnaire. Keep track of how different changes in these factors might influence the ecological footprint. Are some factors more important than others to the ecological footprint? Discuss them with your class.

If you ask students in the class to calculate their own ecological footprint, you should keep several things in mind. First, they will likely need to get help from their families to answer some of the questions. Second, you should ask students to keep their individual footprints private—although you could certainly discuss the range of footprints represented in the class using the anonymous scores.

You don't want any students feeling bad or being publicly ostracized because their ecological footprint is particularly large (or small!). This exercise will help students understand more about how their family lifestyle connects with natural resources, but they are not in charge at home (one hopes) and thus should not be held accountable.

The Ecological Footprint website also asks for a suggestion on what percentage of the planet might be set aside for use by species other than humans. Upon receiving your response, the site shows how many planet earths would be required to support each member of the present human population at the standard of living of the person who answered the questionnaire.

As the authors point out, the calculation presented on the website is a gross simplification and does not take into account many details that might add or subtract from your footprint. Also, those Americans who live an atypical lifestyle, for example by not owning cars, eschewing new products, growing and/or canning their own food, living on a boat, or buying less material goods, may not be represented accurately by this calculation.

A Place in Nature
The way people think about their place in nature is important. If nature is seen as remote wilderness, people are less likely to see that they are part of it. But if the natural world is observed in the familiar settings where we live, particularly where high densities of people live, they are more apt to protect and defend it for present and future generations to enjoy. This feeds back to a higher quality of life.

A Place in Nature
Ask your students where they see nature in their town or city. Are there parks or greenbelts? Landscaping around office buildings? Ponds or streams? Golf courses or backyards? Ask them what kinds of animals live there. The charismatic animals will probably be mentioned first (e.g. squirrels, raccoons, deer, foxes, seagulls, songbirds, hawks, butterflies, bass) but be sure that they think about some of the others too (rats, cockroaches, worms, mosquitoes, carp, catfish, alligators, godzillas).

How many different kinds of animals did you come up with? Were the students surprised at the diversity of life in an urban or suburban setting? How well does your community provide for the environmental needs of these animals? Are there green "corridors" for migrating birds and mammals?

Visit the Baltimore Ecosystem Study and Central Arizona—Phoenix Long-Term Ecological Research websites to see how these projects are cataloging nature in the city.

My Hometown

In 1985, singer-songwriter Bruce Springsteen recorded a poignant song about a dying city. He sang of the innocence of a boy sending young roots down, then the sadness of racial conflict and the wrenching loss of a major employer. The song ends as the boy, now an adult, and his wife are contemplating leaving their hometown for better opportunities elsewhere. If you can find a recording of this, play it for the class to set up the next exercise.

My Hometown
In this exercise, students will discuss the kind of hometown in which they would like to live. Perhaps some of them already live in a community that contains the housing, shops, workplaces, schools, parks, and civic facilities essential to the daily life of the residents.

How big? ?
Explore with your class how a community could work without depending on the car. What if the size of the community was such that housing, jobs, daily needs, and other activities were within easy walking distance of one another? How big might such a town or city be? Could a city be comprised of several such communities, connected by mass transit? Would more people commute by bicycle if they did not have to share the road with cars?

What kind of roofs over our heads? ?
Citizens of many ages might live in your community. It might also include wealthy and not-so-wealthy people. Discuss the diversity of housing types that might enable citizens from a wide range of economic levels and age groups to live there.

What is downtown? ?
A community downtown can be much more than a high-density shopping/motel/fast-food strip. Talk with the class about the center focus for the city that might combine commercial, civic, cultural, and recreational uses. What might it look like? Would there be open space in the form of squares, greens, and parks? How could such public spaces encourage the attention and presence of people at all hours of the day and into the evening?

How will we get around? ?
Brainstorm with students how streets, pedestrian paths, and bike paths might provide a system of fully-connected and interesting routes to all destinations. How could their design encourage pedestrian and bicycle use? (Hint: by being small and spatially defined by buildings, trees, and lighting; and by discouraging high-speed traffic.)

What about places we want to be and need to visit? ?
Ask students to think through where regional institutions and services (government, stadiums, museums, farmer's markets, etc.) should be located. It might make sense to have them near the core of the city, or at the least along mass transit routes.

What else do we want there?
Are there other features of "My Hometown" that would make it a good place to live? How about employers with good-wage jobs? A college or other advanced education institution? Community-building traditions centered on local history (e.g. fairs, festivals, parades, etc.)?


Devote a large wall space (e.g., bulletin board) in your classroom to an oversize map of your community (or town or city). It does not need to be perfectly to scale, but it should represent several elements, including: natural (parks, woodlands, meadows, rivers, streams, lakes), built (commercial, government, recreation, education, housing, industrial, other), and transportation (train tracks, roads, bike/hike trails, mass transit, ferries). If agricultural or forest lands are nearby, they should show up, as should any unique features of your area. Be sure that all of the students participate in the map building (both intellectual and physical).

Finish it off with a colorful border. Have students working in pairs make footprints. One should trace the bare foot of the other, then vice versa. They can color in their footprints any way they like, including with solids, patterns, or photos clipped from old magazines. Attach the footprints around the community map. Take plenty of pictures of the map-making and footprint-making for posterity and the end-of-year nostalgia book.

Upon completion of this lesson, students will understand that cities enable energy efficiency, mass transit, recycling, and other benefits that are difficult or impossible in areas where the density of people is less. They will also have a better appreciation for the features of a city or town that make it a more pleasant place to live, as well as the nature that is in cities.


If students wish to look into livable communities more extensively, they might visit Local Government Commission for an excellent discussion of what makes a community a pleasant place to live.

The Birmingham, Alabama Magic City Math Trail provides outstanding examples of math activities and problems that will help city students see what is around them in different ways.

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