A key “feature” of a tree is that trees sequester carbon –  the process of removal and long-term storage of carbon dioxide (CO2) from our atmosphere.

EcoMatcher and its tree-planting partners estimate that the trees planted sequester CO2 at an average of 25 kilos per tree per year; we use an average of 250 kilos over a tree’s lifetime. Please note those are average numbers as multiple different species are being planted.

The rate of carbon sequestration depends on the growth characteristics of the tree species, the density of its wood, the location’s conditions for growth, and the plant stage of the tree.

That said, there are ways to estimate a tree’s CO2 sequestration, see below^[1].

Step 1: Determine the total green weight of the tree

The green weight is the weight of the tree when it is alive. First, you have to calculate the green weight of the above-ground weight as follows:

W_above-ground= 0.25 D² H (for trees with D<11)

W_above-ground= 0.15 D² H (for trees with D>11)

W_above-ground= Above-ground weight in pounds

D = Diameter of the trunk in inches 
H = Height of the tree in feet

The root system weight is about 20% of the above-ground weight. Therefore, to determine the total green weight of the tree, multiply the above-ground weight by 1.2:

W_{total green weight} = 1.2* W_above-ground

Step 2: Determine the dry weight of the tree

The average tree is 72.5% dry matter and 27.5% moisture. Therefore, to determine the dry weight of the tree, multiply the total green weight of the tree by 72.5%. 

W_{dry weight} = 0.725 * W_{total green weight}

Step 3: Determine the weight of carbon in the tree

The average carbon content is generally 50% of the tree’s dry weight total volume. Therefore, in determining the weight of carbon in the tree, multiply the dry weight of the tree by 50%.

W_carbon = 0.5 * W_{dry weight}

Step 4: Determine the weight of carbon dioxide sequestered in the tree

CO2 has one molecule of Carbon and 2 molecules of Oxygen. The atomic weight of Carbon is 12 (u) and the atomic weight of Oxygen is 16 (u). The weight of CO2 in trees is determined by the ratio of CO2 to C is 44/12 = 3.67. Therefore, to determine the weight of carbon dioxide sequestered in the tree, multiply the weight of carbon in the tree by 3.67.

W_{carbon-dioxide} = 3.67 * W_carbon

Example of CO2 calculation

Tree details:

• 10 years old tree
• 5 meter tall or 16.4 feet tall (“H”)
• 25 cm trunk or 9.8 inch trunk (“D”)

W_above-ground= 0.25 D² H= 0.25(9.8²)(16.4) = 394 lbs

W_{total green weight} = 1.2* W_above-ground= 1.2 * 394 = 473 lbs

W_{dry weight} = 0.725 * W_{total green weight}= 0.725 * 473 = 343 lbs

W_carbon = 0.5 * W_{dry weight}  = 0.5 * 343 = 171.5 lbs

W_{carbon-dioxide} = 3.67 * W_carbon  = 3.67 * 171.5 = 629 lbs CO2 sequestered in 10 years; that equals 285 kg. EcoMatcher uses an aeverage of 250 kg CO2 sequestered per tree.

Ultimately, the growth of each tree is non-linear, and the greatest sequestration stage is in the younger stages of tree growth, depending on rates and peaks of individual species, with the sequestration of CO2 per year dropping thereafter. CO2 sequestration can differ even within tree species, with multiple factors such as growth conditions also at play. But while the exact CO2 sequestration rates may require more accurate measurements to pinpoint, the impact trees can create is undeniable in our global fight against climate change, in addition to the host of localized functions it can fulfill.

^[1]https://www.unm.edu/~jbrink/365/Documents/Calculating_tree_carbon.pdf (University of New Mexico).

#treeplanting #carbon #sequestration #climateaction #carbondioxide

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