Activity: Trees Made of Air (40 minute) Students measure the diameter of the canopy of a local tree and calculate how much carbon the tree sequesters. They compare this to the amount of carbon emitted by the average car and discuss the possibility of offsetting car carbon emissions with trees. Materials needed per pair of students Ball of string Meter stick or measuring tape Calculator Resources Provided Trees Made of Air Worksheet (1 per student) Assessing Trees Made of Air Worksheet Setup Print one copy per student of Trees Made of Air Worksheet. To measure the canopy of a tree, students will need a ball of string and a measuring tape or yard stick. This activity is designed for students working in pairs with each pair picking a different tree. Alternatively, students can bring in measurements from trees in their community. Directions 1. Students determine the diameter of the canopy of a local tree following Trees Made of Air Worksheet. Have students read the introduction and answer question 1. Then discuss the trees they will be studying. It is helpful if the class examines several types of trees. You can direct students to trees at or near the school or have them choose a tree from their community. Directions for how to measure the diameter of a tree’s canopy are on the worksheet. You may choose to demonstrate the technique before students go outside. (Note that this activity can be done in the winter. Direct students to stand under the outermost fine branches to take their measurement.) 2. Students calculate the amount of carbon sequestered by the tree. Students follow steps in questions 2 and 3 to calculate the amount of carbon sequestered by the tree they measured. Note that some students may have trouble converting centimeters to meters or squaring the radius. You can direct successful students to help others. 3. Students compare carbon sequestered by tree per year to average car emissions. students answer question 4 and discuss their answers. Possible discussion questions: How many cars do our collective families drive? Are there enough trees in our community to sequester the amount of carbon emitted by that many cars? What if we consider the cars of everyone in the school or our community? If we wanted to plant enough trees to offset our car use, where would we put them? Assessment Question 1 is the main assessment item. It is an indicator of how well students understand the process of photosynthesis. Students’ answers to question 3 demonstrate their ability to see photosynthesis and combustion as reactions that move carbon dioxide out of and into the atmosphere. Tips You may choose to model the calculations that students will need to do. Extending the Learning – Digging Deeper 1. Factors affecting the rate of photosynthesis Students can explore how climate and tree species affect the amount of carbon a tree sequesters using a Forest Service Calculator. They can compare carbon sequestered by different types of trees of the same size or the same type and size of tree in different climates. Below are instructions for using the CUFR Tree Carbon Calculator from the US Forest Service (https://www.fs.usda.gov/ccrc/tools/tree-carbon-calculator-ctcc). In the spread sheet, enter the following: Flag 1 = 1 Flag 2 = 1 Climate zone – choose whichever number best fits your location – for example, 12 Midwest Species code and scientific name – find the name of the tree from the drop down menu. Once you enter it, the scientific name should appear in the white box to the right under Description. – for example, QURU (Quercus rubra) Note that this calculator does not use the metric system. Diameter at breast height (D.b.h.) must be in inches. The approximate height (for example, 23 feet) should appear in the white box to the right under Description. The results are shown in the last 3 columns of the Carbon Calculator Results (annual) section. CO2 sequestration _179 ___ kg CO2per year Total CO2 stored __4660 __ kg CO2 per tree Above-ground biomass (dry weight) __1980_ kg per tree To convert kg CO2 to kg carbon, students need to multiply by 0.27. 2. Total carbon sequestered This information is also available from the Forest Service calculator. Again, to convert kg CO2 to kg carbon, students need to multiply by 0.27. Fate of sequestered carbon The carbon remains sequestered only so long as the tree remains alive. If it dies and decomposes or is cut and burned, the carbon in it will end up as CO2 in the atmosphere. Only if it is turned into something, such as furniture or housing material will the carbon remain sequestered. Students may think that a “natural” process such as decay is better for the environment that using the wood for construction. Decay does return the nutrients such as nitrogen to the soil. However, it also returns the carbon to the air.
