As trees vary in size and shape from species to species, so does their carbon trapping power. Most state forestry divisions have resources to help students identify tree types. A quick discussion of the types of trees--deciduous, hardwoods, softwoods, evergreens--will prepare students to recognize trees better as they get ready to measure the size of the trees. Printing guides to tree identification for field use will help students to track the carbon trapping capabilities of the trees in their surroundings.
Once you are confident the students can identify various types of trees, it is time to head outside. If your school is blessed with surrounding trees, measure those. If there are not many trees on school property, arrange a field trip to a more suitable location if possible. Students should work in pairs or trios. Each group must have its own tape measure, tree identification guide and a notebook and pencil to record the circumference of each tree in centimeters. Taking photos of the trees also will aid in classroom identification.
Have each group maintain its own list for individual calculations. Combine all the lists to determine the carbon trapping impact of the trees selected. Use the free, dowloadable Tree Carbon Calculator linked in the References section to do so. This handy, online calculator is available in a self-extracting zip file that can be unzipped to run the program on your computer. It has species-specific information regarding how much carbon different types of trees at various sizes store.
The U.S. Forest Service estimates that each person creates 2.3 tons of carbon dioxide per year while one acre of healthy trees on average "traps" or "stores" 2.6 tons of carbon dioxide per year. Unfortunately, there isn't an acre of trees for every person. By learning to calculate the benefits of just one tree and then following up by planting a tree, students will learn to take personal responsibility for the effects their daily activities have upon the environment.
Most students will have access to trees in their home environment. The trees may be located in their own yard or at a nearby park. Assign each student to determine the carbon trapping capabilities of 10 trees in their neighborhood. Have each student determine if there are enough trees in their surroundings to counteract their estimated carbon footprint.