Living in a Carbon World

Part B: Carbon Storage in Local Trees

Adapted from Janowiak, M.: "The Carbon in Trees" activity from Future Fuels from Forests Teacher Institute. 2009, Northern Institute of Applied Science , Michigan Technological University.

You may have a favorite tree nearby in your own backyard, outside your school or in your neighborhood. How much carbon do you think this tree stores? You can easily determine the amount of carbon stored in your favorite tree using simple materials and calculations. First, watch forest ecologist Laura Marx describe carbon storage in a Red Oak tree in a Massachusetts forest. As you watch, write down three facts about carbon storage in trees you think it is important to share with the class before you begin this activity.

NOTE: If this video does not play, watch here: Forest Carbon 101

Discuss

As a class, share and discuss the three facts you wrote down about carbon storage in trees. Then, dicuss the following question:
  • Why should we care about how much carbon a tree stores?

  • Lab investigation: How Much Carbon is Stored in a Local Tree?

    In this activity, you will determine the amount of carbon stored in a local tree. You will develop a set of skills that you can use on many species of trees, from urban trees to trees in the middle of forests. These skills include:

    1. Watch this Vimeo video on how to measure trunk diameter before going outside to select a nearby tree to study. Make note of important instructions. If the video doesn't play, watch here: Trunk Diameter: Learn To Measure on Vimeo
    2. Select a local tree with a circumference of at least 38 cm (15 inches), if possible. Assign your tree a number. NOTE: Each tree should have a different number.
    3. Identify the species and common name of the tree using a tree ID guide or a tablet APP. (NOTE: You will need to choose a species of tree whose common name is on the table of Allometric Coefficients for Common North American Trees (Microsoft Word 2007 (.docx) 91kB Jan30 15)
    4. Take a picture and/or make drawings of the tree. You may want to include other information such as GPS location and environmental variables that might impact the growth of the tree (for example, soil type, soil moisture, soil nutrients (NPK fertilizer), amount of light the tree gets, temperature etc.)
    5. Is this species a hardwood or softwood? in general, hardwood comes from deciduous trees and has denser wood than softwood trees, which come from conifers. The resources you used to help identify your tree species should tell you if your tree is a hardwood or softwood. If not, use this resource Hardwood or Softwood?
    6. Determine the diameter (cm) of the tree trunk at 1.4 meters (4.5-4.6 feet) from the ground. Use one of the two following methods:
      • Use a diameter tape measure to directly measure diameter. Convert to centimeters (cm) if necessary.
      • Use a regular tape measure or string to measure the circumference of the tree. Convert the circumference measurement to centimeters(cm) if necessary. Divide the circumference(cm) measurement by 3.14(Pi) to calculate the diameter.
    7. Calculate the biomass (M) for your tree. To calculate tree biomass, foresters use a standard allometric equation M=aDb where:
      M= above ground dry weight biomass(kg) of the tree

      D= diameter measured at 1.4 meters (4.6 feet above ground)

      "a" and "b" are species-specific allometric coefficients. Locate these two coefficients for the common name of your tree on the Allometric Coefficients for Common North American Trees (Microsoft Word 2007 (.docx) 91kB Jan30 15) table.
    8. Calculate the approximate mass of carbon atoms stored in your tree in kilograms(kg). .
      A tree's biomass contains carbon atoms in addition to hydrogen, oxygen nitrogen, phosphorus and sulfur atoms. Foresters know that approximately half of a tree's biomass is made of carbon atoms. This value is slightly different in hardwood vs softwood trees. To determine the amount of carbon in your species of tree, choose one of the following:

      Multiply tree biomass (M) by 0.521 for hardwood trees =____(kg) of carbon stored

      Multiply tree biomass (M) by 0.498 for softwood trees = _____(kg) of carbon stored



    9. Calculate the approximate amount of CO2 your tree absorbed via photosynthesis to create its stored mass of carbon. NOTE: Not all CO2 a tree takes in gets stored as mass. Some returns to the air via respiration. Scientists have determined that 1 kg of carbon is equivalent to approximately 3.67 kg of CO2. Thus, multiplying the carbon stored (kg) in your tree by 3.67 will give you an approximate measure of CO2 taken in via photosynthesis and stored in the tree.


      Checking In

      How many kg of CO2 did your single local tree remove from the atmosphere and store in its biomass?
    10. (Optional) Convert the mass of carbon stored in your tree to metric tons. NOTE: Scientists normally use metric tons to quantify carbon storage. Do a simple calculation using this conversion factor (1 metric ton = 1000 kg) or use the worldwide metric calculator.
    11. Use a spreadsheet program to input the following variables into separate columns in a class data spreadsheet:
    • tree number
    • tree species
    • common name
    • hardwood or softwood
    • biomass(kg)
    • mass of carbon(kg)
    • CO2 absorbed(kg)

    Discuss

    As a class, discuss the following:
    • What is the best way to display your tree data? Think in terms of the following:
      • important ways to sort the data in the spreadsheet
      • identifying the variables that are most important to graph
      • types of graph(s) you should construct to represent the data
    • After graphing is completed, analyze and discuss the graphs in terms of the following:
      • interesting patterns that emerge from the data(if any)
      • amount of carbon stored (sequestered)
      • amount of CO2removed from the atmosphere by the trees and stored in tree biomass.
    • What environmental variables, if any, could influence the amount of carbon stored by trees. How?
    • Think about the carbon storage data your class has collected and the skills you have gained to collect that data. How might tree carbon storage data and your new skills be useful to your community?

    Stop and Think

    1: Carbon dioxide (CO2) is a greenhouse gas that naturally warms the atmosphere as part of the greenhouse effect. Unfortunately, the amount of CO2 in the atmosphere has been increasing over the past hundred years. According to scientists, this increase in atmospheric CO2 has caused the average global temperature on Earth to increase by about 0.8° Celsius (1.4° Fahrenheit) since 1880. Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade. (NASA)

    Optional Extensions

    Want to learn more about trees, and the carbon cycle? Check out these resources:

    • Research the latest research! New research on the carbon cycle, climate and the environment is on-going. You can use ScienceDaily and Phys.org to research recent research on carbon storage in trees and forests by using combinations of the following tags: carbon cycle, carbon storage/sequestration,trees, forests, carbon sink. Here is an example: Munching bugs thwart eager trees, reducing the carbon sink
    • Explore San Francisco's UrbanForest Map project to measure and map tree carbon in urban trees. Do you have a similar program in your community?
    • Read Over three million trees killed by the 2011 Texas drought.
    • Use the TreeBenefits Calculator to find out how your tree benefits your community. Putting in your tree name and your zipcode will take you to the tree benefits page. In addition to other tree benefits, you can click the CO2tab in the menu to find out the benefits of your tree sequestering CO2.