How To Calculate CO2 in Trees by Dr. Michael A. Bengwayan

How To Calculate CO2 in Trees

How to calculate the amount of CO  sequestered in a tree per year

Prepared by

Dr. Michael A. Bengwayan

Director

Cordillera Ecological Center (PINE TREE)

The Cordillera Ecological Center (PINE TREE) , Philippines  estimates that trees planted either for reforestation , afforestation and agroforestry in the Cordillera region, having a tropical climate, will sequester atmospheric carbon dioxide at an average of 50 pounds of carbon dioxide per tree per year.

The rate of carbon sequestration depends on the growth characteristics of the tree species,

the conditions for growth where the tree is planted, and the density of the tree’s wood. It

is greatest in the younger stages of tree growth, between 20 to 50 years. Complicating the issue is the fact that far less research has been done on tropical tree  species as compared to temperate tree species.

Nevertheless, I  can roughly estimate the amount of CO2 sequestered in a given tree,

by dividing the tree’s get a yearly sequestration rate.

This process:

1.  Determine the total (green) weight of the tree.

2.  Determine the dry weight of the tree.

3.  Determine the weight of carbon in the tree.

4.  Determine the weight of carbon dioxide sequestered in the tree

5.  Determine the weight of CO sequestered in the tree per year

1. Determine the total (green) weight of the tree

Use the following algorithm:

W = Above-ground weight of the tree in pounds

D = Diameter of the trunk in inches

H = Height of the tree in feet

For trees with D < 11:

W = 0.25D2H

For trees with D > 11:

W = 0.15D2H

Depending on the species, the coefficient (e.g. 0.25) could change, and the variables D

and H could be raised to exponents just above or below 1.  However, these two equations

could be seen as an “average” of all the species’ equations.

The root system weighs about 20% as much as the above-ground weight of the tree.

Therefore, to determine the total green weight of the tree, multiply the above-ground

weight of the tree by 120%.

2. Determine the dry weight of the tree

Studies show that  the average tree is 72.5% dry matter and 27.5% moisture.

Therefore, to determine the dry weight of the tree, multiply the weight of the tree by

72.5%.

3. Determine the weight of carbon in the tree

The average carbon content is generally 50% of the tree’s total volume.   Therefore, to

determine the weight of carbon in the tree, multiply the dry weight of the tree by 50%.

4. Determine the weight of carbon dioxide sequestered in the tree

CO2 is composed of one molecule of Carbon and 2 molecules of Oxygen.

The atomic weight of Carbon is 12.001115.

The atomic weight of Oxygen is 15.9994.

The weight of CO  is C+2*O=43.999915.

The ratio of CO  to C is 43.999915/12.001115=3.6663.

Therefore, to determine the weight of carbon dioxide sequestered in the tree, multiply the

weight of carbon in the tree by 3.6663.   sequestered in the tree per year

5. Determine the weight of CO

Divide the weight of carbon dioxide sequestered in the tree by the age of the tree.

Et voila!  Congratulations!

EXAMPLES

Estimated growth rates and sizes of  trees were taken from the World

Agroforestry Centre’s “Agroforestree Database” :

Let’s see how much a Calliandra calothyrsus might sequester in a year.  A 10-year-old

Calliandra would probably grow about 15 feet tall with a trunk about 8 inches in

diameter.  Therefore:

W = 0.25D2H

H = 0.25(8 )2(15) = 240 lbs. green weight above ground.

240 lbs. * 120% = 288 lbs. green weight (roots included)

288 lbs. * 72.5% = 208.8 lbs. dry weight

208.8 lbs. * 50% = 104.4 lbs. carbon

104.4 lbs * 3.6663 = 382.8 lbs. CO2 sequestered

382.8 lbs / 10 years = 38.3 lbs. CO2  sequestered per year

Or consider a 10-year-old Grevillia robusta, 45 feet tall with a trunk 6 inches in diameter.

Using the same calculations as above, the amount of CO2  sequestered would be 64.6 lbs.

per year.

Or a newly-planted Acacia angustissima, 2.5 years old, 15 feet tall with a trunk 3 inches

in diameter: 21.5 lbs. of CO2 sequestered per year.

Or an Albizzia lebbek, 15 years old, 30 feet tall, with a 12 inch trunk: 68.9 lbs. of CO2

sequestered per year.

Because PINE TREE has been planting Caliandra calothyrsus since 1992, we can easily calculate the carbon sequestered by our trees. Thank you.  MICHAEL A. BENGWAYAN, Ph.D.