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Balancing Act: Urban Trees and the Carbon Cycle

This article is from Issue Urban Forest - Vol. 6 No. 1.

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Too much carbon dioxide (CO2) in the atmosphere is mostly caused by two things: burning fossil fuels and the loss of trees. Urban trees help to keep urban areas cooler, they hold soil in place, they make urban areas prettier, and they help to keep urban areas quieter. They also absorb CO2 from cars, buses, and the many engines that are used in urban areas. When people plant and maintain urban trees, they usually use machines with engines which emit CO2. When a tree is cared for using machines with engines, there is a point in the tree’s lifetime at which more CO2 will be emitted from the engines than the tree has absorbed. The scientists wanted to know which tree species can grow the longest before reaching that point.

Welcome to the Urban Forests edition

Note to Educators

Urban Forest Lesson Plan

Reflection Section Answer Guide

Education Standards Correlations

Meet the scientists that contributed to this article:

"Science Topics" covered in this article:
  • Earth Science
  • Life Science
  • People and Science
  • Technology and Science

"Environmental Topics" covered in this article:
  • Atmosphere (Educators)
  • Forest and Grassland Use (Educators)
  • Growing and Using Trees and Other Plants (Students)
  • Importance of Forest to People (Students)
  • Using Forests (Students)
  • Vegetation Management (Educators)

Regions covered in this article:
  • Alaska
  • Forest Products Lab
  • Intermountain
  • International Institute of Tropical Forestry
  • Northern
  • Pacific Northwest
  • Pacific Southwest
  • Rocky Mountain
  • Southern
  • Southwestern

"Thinking About Science Themes" covered in this article:
To discover new things, scientists must work with information. They may take old information and look at it in new ways. They may collect new information and consider it in ways that no one has done before. Often, the information that scientists collect and consider is in the form of numbers. The numbers represent quantities of whatever it is the scientists are studying. In this study, the scientists were interested in carbon dioxide, or CO2. The scientists estimated the amount of CO2 absorbed by urban trees. They compared that number with another number. The other number indicated how much CO2 was put into the atmosphere when machines were used to plant and maintain urban trees. Thus, they were looking at how much CO2 was either being absorbed or emitted by planting and maintaining urban trees. By using numbers, the scientists could better understand how the management of urban trees affects the carbon cycle.
Specific "Thinking About Science" Themes:
  • Characteristics of Scientists
  • Scientific Topics
  • The Scientific Process
  • Uses and Benefits of Science

"Thinking About Environmental Themes" covered in this article:
Carbon is one of the most interesting and widespread of elements. All plants and animals on Earth, including humans, are made up of carbon. Much of Earth's carbon is held deep in Earth as petroleum, coal, and natural gas. These forms of carbon are used by humans as fossil fuels to run machinery. In the carbon cycle, carbon moves from the atmosphere, to Earth, into Earth, and back to the atmosphere (figure 1). When fossil fuels are burned in engines, carbon is taken from inside the Earth and then emitted into the atmosphere as CO2. If humans did not burn fossil fuels, the carbon cycle would stay in a natural balance. Too much CO2 in the atmosphere disrupts Earth's climate and can cause the Earth's global temperature to rise.
Specific "Thinking About the Environment" Themes:
  • Cycles

NSE Standards covered in this article:
  • Abilities necessary to do scientific inquiry (A)
  • Nature of science (G)
  • Personal health (F)
  • Populations and ecosystems (C)
  • Populations, resources and environments (F)
  • Properties and changes of properties in matter (B)
  • Regulation and behavior (C)
  • Risks and benefits (F)
  • Science and technology in society (F)
  • Science as a human endeavor (G)
  • Understandings about scientific inquiry (A)

Science Benchmarks covered in this article:
  • Common Themes: Constancy and Change
  • Common Themes: Systems
  • Habits of Mind: Critical-Response Skills
  • Human Society: Social Trade-Offs
  • The Living Environment: Flow of Matter and Energy
  • The Living Environment: Interdependence of Life
  • The Nature of Science: Scientific Inquiry
  • The Nature of Science: The Scientific Enterprise
  • The Nature of Science: The Scientific World View
  • The Nature of Technology: Issues in Technology
  • The Nature of Technology: Technology and Science
  • The Physical Setting: The Earth