How much carbon is in a tree?
Adapted from a lesson by Denise Payment
Learning Objectives
Students will measure a tree of known species and determine its diameter,
height, and calculate carbon mass using mathematical equations.
Students will compare the carbon content of trees studies by their class
Materials (per group of 3)
tape measure or diameter tape, tree identification book, clinometer,
handout to calculate carbon mass, calculator, and allometric equation for
tree species (See student handout), clipboard, pencil, digital camera and
GPS (optional). Use metric units.
Procedure
1. Hand out supplies to groups of students. Some supplies may need to be shared by groups.
Have students make clinometers if necessary; instructions are at
http://oceanservice.noaa.gov/education/lessons/how_high_that.html .
2. Take students outside to an area of trees that is easily accessible during the school year. (Be
sure to get permission or notify the office of whereabouts)
3. Have students choose a tree. Discuss beforehand that some of the trees may not be native to
your region. Identify the tree species using a tree identification book or guide. You may want
to select and tag trees for the study ahead of time.
4. Have students take a picture and make drawings in the journal of the bark, leaves, twigs, buds,
etc. Date drawings. An optional GPS coordinate may also be taken.
5. Have students follow instructions on the student worksheet to measure and calculate the
height of their tree.
6. Demonstrate height at which students need to measure the diameter of the tree. This is referred
to as diameter at breast height (DBH)- 4’5”. Measure using a diameter tape or calculate the
diameter by finding the circumference in centimeters.
7. Complete student worksheet “Calculating carbon in a tree” to determine mass of carbon in the
tree. Calculate the value of the carbon in the tree at a rate of $15 per metric ton.
8. Record carbon mass of tree in classroom table and depict the information in a chart
9. Calculate all the carbon sequestered in the trees the students have adopted, and enter the data
into a table on the board separated into categories for conifers and deciduous trees.
10. Discuss with students where the carbon comes from. Review photosynthesis, pointing out the
role of carbon molecules.
Student Worksheet to determine the height of a tree
Measure the distance from the base of the tree on a meter tape out to where you can see the
top of the tree
(b): _________________ m
Use a clinometer or protractor to measure the angle from the horizontal to the top of the
tree
(A):__________ degrees
Measure the distance from the ground up to observer’s eyes
(z):_________ m
Use the tangent of angle "A" to calculate the height of the tree
H = ((tanA x b) + z
H = ________________m
Student worksheet for calculating carbon in a tree
1.) Measure the circumference at breast height (in cm): __________________
2.) Calculate the diameter at breast height (in cm): ___________________
(Remember: Diameter = circumference/pi)
3.) Identify the species: ____________________
4.) Calculate the biomass of your tree or shrub (in kg): ____________________
The formula for this is M=aDb
The values for a and b for many species are given in the table following the worksheet
M= biomass
a= species coefficient a (See Table 1 on page 2.)
D= diameter at breast height
b= species coefficient b (See Table 1 on page 2.)
Is this species hardwood or softwood? (The resources you used to help identify your tree
species should tell you if it hardwood or softwood.) ______________________
5.) Calculate the amount of carbon in your tree or shrub (in kg): __________________
To do this:
Multiply biomass (M) by 0.521 for hardwood trees.
Multiply biomass (M) by 0.498 for softwood trees.
6.) You may wish to convert kg to tons to make comparisons between your measurement
and the measurement of greenhouse gases in the air: ______________
(1 metric ton = 1000 kg)
Example:
Diameter of a beech tree is measured at 75 cm
Values for beech are a= .0842 b= 2.5715
Formula is M = aDb
M = .0842 (75 ^ 2.5715)
M = 5585.12 kg
Beech is a hardwood, so multiply by 0.521 =
Divide by 1000 kg per ton
2909.8 kg carbon in the tree
= 2.91 metric tons of carbon
At $15 per ton, the carbon in the tree would be worth $43.65
TABLE 1
Species-Dependent Coefficient and Exponent Values for Biomass Equation
Tree Species
a
b
Ash, white
.1063
2.4798
Basswood
.0617
2.5328
Beech
.0842
2.5715
Birch, black/sweet
.0629
2.6606
Cedar, Red
.1019
2.3000
Cherry, Black
.0716
2.6174
Cherry, Sweet
.1556
2.1948
Elm, American
.0629
2.6606
Elm, slippery/red
.0629
2.6606
Black Locust
.0792
2.6349
Flowering dogwood
.0792
2.6349
Hackberry
.0792
2.6349
Hemlock
.0622
2.4500
Hickory, mockernut
.0792
2.6349
Hickory, pignut
.0792
2.6349
Hickory, shagbark
.0792
2.6349
Hop hornbeam
.0792
2.6349
Hornbeam
.0792
2.6349
Maple, Red
.0910
2.5080
Maple, Sugar
.2064
2.5300
Oak, black
.0904
2.5143
Oak, chestnut
.0554
2.7276
Oak, red
.1130
2.4572
Oak, white
.0579
2.6887
Pine, white
.1617
2.1420
Sumac, Staghorn
.0825
2.4680
Values taken from: The Yale University site-
http://www.yale.edu/fes519b/saltonstall/biomass2.html - estimate
Note: Scientists continue to research different ways of determining the a coefficient and the b
exponent, so you may choose to different values based on different research.