Carbon Sequestration in Campus Trees

Robert S. Cole, Spreadsheets Across the Curruculum; Washington Center; Science Education Resource Center (SERC)

In this activity, students use a spreadsheet to calculate the net carbon sequestration in a set of trees; they will utilize an allometric approach based upon parameters measured on the individual trees. They determine the species of trees in the set, measure trunk diameter at a particular height, and use the spreadsheet to calculate carbon content of the tree using forestry research data.

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Notes from our reviewers

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If this activity is being done for the first time, it will serve as a baseline for future, follow-up projects by other students. This module is best used when data on a given set of trees are available from prior years, but establishing a solid baseline is important for all scientific measurements. Assuming that data from field measurements are available to students, this module could be used as a homework exercise, or as a lab exercise. The module is also useful in teaching about how ecologists and biologists use allometric relationships as well as teaching about the power function. An instructor version of the PowerPoint, with the cell equations for the embedded spreadsheets, is available upon request: [http://www.evergreen.edu/washcenter/modules/request.asp?m=SSAC2006.QC879.8.RC1.1]
The resource guides students through the process of estimating tree biomass from measurements of tree diameter at breast height and the use of the allometric relationship between growth and size of one portion of a tree and the growth and size of the whole tree. Instructor can assign this as is (using the example data set to teach the process) or can add enrichment, including a campus tree survey in collaboration with groundskeeping. Opportunity to stress the global seasonal flux of CO2 due to plants in the Northern Hemisphere absorbing CO2 from the atmosphere through photosynthesis in the spring and summer and releasing carbon through decay into the atmosphere in the fall and winter. Comments from expert scientist: It makes users think about the age of the trees and how their uptake compares to our emissions. It may give a simplistic idea of carbon sequestration without considering the drawbacks of large forest stands. Having a lot of trees around may be good for carbon sequestration, but on watersheds trees crowd out grasses which are much better for precipitation infiltration than a thick forest.
This module consists of a PowerPoint presentation with background materials and instructions on how to recreate the embedded images of spreadsheets. The students develop the needed cell formulas and complete the spreadsheet to estimate the amount of carbon stored in the tree's biomass. Students build quantitative skills and skills working with Excel spreadsheets. Manipulating spreadsheet models may be engaging for some students. If the instructor chooses to do a tree inventory on campus, students may be more engaged in the activity, as it is more applicable to their lives. Little teacher support, other than guidance, is required for this exercise.