Urban Ecosystems 1: Cities Are Urban Ecosystems


  • String
  • Magnifying glasses
  • Flip-chart type paper
  • Tape
  • Colored markers
Urban Ecosystems 1: Cities Are Urban Ecosystems Photo Credit: Science NetLinks


To understand that cities are urban ecosystems which include both nature and humans, in a largely human-built environmental context and that urban ecosystems have emergent properties that cannot easily be seen by simply looking at the different functional parts of a city: The whole is more than the sum of the parts.


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 first 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 vs. cyclic. Finally, students will look at some of the positive environmental features of urban ecosystems.

Urban Ecosystems 1 introduces some of the principles of ecology, including the definition of an ecosystem as a community of living organisms interacting with its non-living environment. Students will be introduced to the study of ecosystems and models that are used by urban ecologists. The class will be invited to visit websites to see where the cities are on the planet, and they will have a chance to try some hands-on urban nature education activities.

A common student misconception related to this topic is that cities are separate from nature and do not need to be considered in the study of ecosystems. According to urban historians, this view is largely a phenomenon of the Enlightenment and Romantic period, which gathered particular strength in the new United States following the American Revolution. The founders had a strong focus on agrarianism and there were very definite fears of urban growth corrupting American politics and society—as they felt had happened in the Old World.

Another common assumption is that by studying the different parts of a city (transportation infrastructure, parks, economic base, etc.), one can understand how the city functions: this is rarely the case.

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.

Contact Dr. Firth at pfirth@nsf.gov.

Planning Ahead

In addition to the websites listed in the lesson, energy information is nicely presented at the Rocky Mountain Institute website.


Discuss with your class what makes a city. Ask questions such as:

  • Why is a city different from a small town or village?
  • How many people live in our city (or the nearest large city)?

Go to Capital cities and cities of 100,000 and more inhabitants, a page on the United Nations website. Here you can find out the population of cities around the globe, as well as one not too far from you.

Find the United States on the document and look at the table that appears. Show the class that the population of the “city proper” is often much less than the “urban agglomeration.” For example, the city of Atlanta has about 396 thousand people, but the Atlanta metropolitan area has 3.3 million people!

Another interesting way of introducing cities is by looking at some of the things that make cities today different from cities of long ago. The Three Cities website, sponsored by National Geographic, provides interesting points (and images) of Alexandria in year 1, Cordoba in 1000, and New York City in 2000. Take your class to the site and discuss the people, communications, music, and other things shown in the images.


An ecosystem is a community of living things interacting with nonliving things. Examples include forests, lakes, soils, and coral reefs. A city is an urban ecosystem. People are among the living things, and the buildings, streets, and other structures that people build are among the nonliving things.

The word urban has a Latin root that means “city.” Did the Latin scholars just make up the word?

Latin Scholar 1: "Come on Augustus! We've got to come up with a word to describe this big group of houses, temples, markets, roads and common baths."
Latin Scholar 2: "Umm…."
LS1: "Look, I know how creative you are, I'll just write down the next word you say and we can go get some lunch!"
LS2: "Er…."
LS1: "Ur! That's IT! It's short, easy to pronounce, and…"
LS2: "Um, Romulus… you spelled it wrong."
LS1: "No worries. Let's get out of here!"

Well, actually this conversation never happened. In real life, there was an ancient city named Ur located in what is now the country of Iraq. More about Ur later. Back to ecology.

Urban ecosystems occupy only about 2% of the land surface area of the planet, but provide a home for half of the world’s population. That is about 3 billion people. The proportion of people living in cities is even higher in the developed regions of the world. In the United States, more than three-quarters of the people live in urban areas. More than two-thirds of the people of Europe, Russia, Japan, and Australia live in such areas. Where are the cities?

Lights! Action! Cities!
Take your students to the Night Lights Around the World website to see a composite image of the world at night as well as images of North America and Europe.

Ask them to comment on where the urban ecosystems are in relation to coastlines, large rivers, deserts, mountain ranges, rain forests, tundra, ice caps, and other physical features of the planet.

By the way, while the students are gazing at these amazing images, call their attention to how bright the U.S. looks compared with other parts of the planet. Lighting accounts for about a fourth of all electricity used in the United States, consuming the energy produced by 120 large power plants (about 4/5 directly and 1/5 in extra air conditioning energy to remove unwanted heat).

The ordinary incandescent light bulbs used in most homes are a big part of this: They use only approximately 10% of the energy they require for light, and release the rest as heat. These kinds of light bulbs have been described as small, electric space heaters that happen to give off a little light.



Urban heat island effects are created when cities grow and asphalt roads, tar roofs, and other features are substituted for areas where plants would otherwise grow. Because dark surfaces like pavements store heat during the day, which is released at night, they keep cities hotter for longer periods of time. Are there local heat islands in your schoolyard? What color is the roof of the school? The parking lot?

While you are talking about how dark colors absorb and light colors reflect solar radiation, you might introduce the idea that physics is employed by the field of architecture known as green design. Green design takes advantage of some of the fundamental laws of physics in order to minimize the energy that is required to heat and cool buildings and otherwise power our lifestyle. The Green Design website has some excellent links that students may wish to follow to learn more about energy efficiency in home lighting, computers, and other appliances.

Scientists who study urban ecosystems often begin with the landscape: What does it look like? How patchy is it? What nearby features might influence it? They also must consider different kinds of boundaries (e.g. political jurisdictions, neighborhoods, rivers, and other natural features) and think about how these might affect the ecosystem.

One of the most important elements for urban ecosystems is time: The effects of history, lags and legacies, and processes that change suddenly or unpredictably over time. What models can be used for studying urban ecosystems?

Science in Cities
Take your students on a tour of the website for the Baltimore Ecosystem Study. This study aims to understand metropolitan Baltimore as an ecological system by bringing together researchers from the biological, physical, and social sciences. These people are collecting new information—and analyzing and synthesizing existing information—on how the "built" and wild ecosystems of Baltimore work. As a part of the National Science Foundation's Long-Term Ecological Research Network, the researchers also seek to understand how Baltimore's ecosystems change over long time periods.

Divide your class into teams and have the teams study selected research and education projects described on the website and report out to the class.

Ask questions such as the following:
  • How are the different scientists involving history in their work?
  • Are there any research findings that you think your local Mayor and the City Council should know about?
  • What is the difference between a research finding and an action recommendation?

Ecosystems are complex systems. Complexity does not just mean that they are complicated (although that is sometimes the perspective that humans have!). Complexity implies that the ecosystem has what are called “emergent properties.” This is just a sophisticated way of saying that the whole is more than the sum of the parts. The reason complexity matters is that it makes the ecosystem behave in what scientists call a “nonlinear” way.

Easy example:
If you put a little fertilizer in a pond, it will turn green as the algae get the munchies and grow faster. A little more fertilizer, a greener pond. A little more and OOPS the system goes non-linear and fish start to belly up to the surface. Too much of a good thing and the rotting algae used up all the oxygen in the water. Really interesting, and equally non-linear, is how the pond recovers. But we don’t have time for that here. Suffice it to say that simply extrapolating past ecosystem behavior does not always work to forecast future ecosystem behavior. This can have big implications for urban ecosystems and the people who get involved in urban planning.

Complexity Cues
As the number of parts of a system increases, the number of possible interactions between pairs of parts increases much more rapidly. Have your class try to come up with the features of urban ecosystems that make them so complex (and unpredictable) and discuss how these might have changed (or might change) over time.

Some suggestions include:
  • Water cycles and extremes such as floods and droughts (think pavement, runoff…)
  • Nutrient cycles such as nitrogen and phosphorus (think fertilizer, dog and other animal droppings, etc.)
  • Energy flow through natural and human food webs (think grass clippings, autumn leaves, auto fuel, etc.)
  • Geographic and climate setting
  • Formal and informal political arrangements
  • Administrative hierarchies
  • The division of labor
  • The interaction of different professions
  • Modern and ancient technologies
  • Communications such as person-to-person, and others such as signs, radios, etc.
  • Spiritual influences
  • Race and ethnicity
  • Immigrant populations
  • Gender relations
  • Domesticated animals and pets
  • Invasive species
  • Military defenses present and past
  • Economic power and influence

In considering urban ecosystems, we should try to put aside the notion that nature means only majestic mountains, pristine forests, and untamed rivers. There is also nature in cities, it just tends to be a little less obvious.

In the 21st century Western world, our sense of reality may come much more from TV and the Internet than from actual, direct firsthand experience. Silly as it may seem, many students know more about the wildlife of Africa than in their own backyard. Urban nature educators have come up with a wide variety of interesting approaches to help show urban youngsters the environment in their environment. If you are located in an urban area (or not!), try some of the following:

A Micro-Hike
Issue one-meter pieces of string to individuals or teams of students. Outside, have them toss their strings on the ground. If magnifying glasses are available, they should use them. Have the students follow along their string, trying to locate several scenic sights and possibly even diminutive wildlife specimens.

The students then become trail guides, showing the sights to "tourists" from other teams. They should be as creative as possible about the grass jungles, miniature wetlands, dandelion observation towers, ant lion ambush pits, grand canyons, elusive millipedes-of-the-wood-chips, evidence of mammals and birds, and, of course, any monuments or memorials they come across. Extra points for any students that bring the history of the site into their trail guide spiel.

A Scavenger Hunt
Put together a list of shapes, colors, patterns, and specific items (items smaller than a couple of centimeters—an inch—work best). As a class, decide where the boundaries for your scavenger hunt should be. Draw a map of the area you are going to search. Mark the locations of woodsy, grassy, wet, and dry areas you are going to visit. Study the Scavenger Hunt List and discuss in class the deadline for the Scavenger Hunt.

Groups of 3-5 students should try to find as many items as they can. Begin with 20 seconds of uninhibited leaping to burn off the energy that claims the top tier of the students' attention. Then call "time!" and send them off to the hunt.

Can they find a hairy leaf? (Hint: sycamore tree.) An elbowed antenna? (Hint: ant.) A circle that humans did not make? (The sun.) An octagon that humans did make? (Stop sign.)

Be sure to delimit the area that they can search on school grounds, or if this is a home project, send a note for the parents suggesting a certain amount of supervision. Have students share their finds with the class in an old-fashioned show-and-tell. Use an egg timer to be sure everyone gets a chance to show their bit.


Divide the class into teams and equip each team with four or six sheets of flip-chart type paper, tape, and colorful markers. Have them tape the paper together to make a giant poster, and ask each team to draw a representation of what they learned in this lesson. They can have some planning time, but should be given a deadline by which their poster needs to be finished. Everyone needs to participate in drawing or coloring, and put their names around the outside of the work. It does not have to be artistic, just expressive. Then, allow about five minutes per team for a designated speaker or two to explain what they drew and how it represents their understanding of urban ecosystems.

Students may go into this lesson thinking that humans and nature are separate, particularly in cities. The lesson should show them that cities are urban ecosystems that include both nature and humans, in a largely human-built, environmental context. The students will also get an appreciation for the complexity of urban ecosystems and will understand that the whole is greater than the sum of the parts. This is a classic understatement for cities!


Follow this lesson with the next four lessons in the Urban Ecosystems series:

A Spring Project
This is a wonderful, hands-on way to introduce students to the concept of ecological change over time in an urban ecosystem. Have each student select a small patch (1 or 2 meters square) that will be "theirs" from the end of the winter holidays until the summer break begins.

They should spend no less than 20 minutes in their space at least 5 times spaced out over the winter to spring period. When they are there they should be quiet (no music or chit chat) and listen carefully to all of the sounds that they hear. They should record notes on what they see, hear, smell, and touch in their journals. These can be illustrated with pictures they draw as well as measurements (e.g. leaf buds to tiny leaves to mature leaves).

Back in the classroom, they can try to identify some of the plants and animals and fungi that they saw and heard, or discovered evidence of, and consider how they fit into the urban ecosystem. They can also try to relate the micro-environment of their spot to the bigger processes of the natural world (climate, biological diversity, water cycle, etc.) as well as the urban ecosystem (buildings, heat islands, roads, background noise, foot traffic, etc.)

Here are some links to online "field guides" that students can use to identify specimens:

Many other links, including some state and regional online field guides, may be found at the site called The Internet.

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Lesson Details

Grades Themes Project 2061 Benchmarks National Science Standards State Standards