Sunday, July 11, 2010

How much carbon does a tropical tree sequester? (Part 2)

Woody biomass is 50% carbon in tropical trees
Continuing from Part 1 (previous Post), let me cite some additional studies and methodologies. A Dutch study entitled “Estimation of Tropical Forest Biomass for assessment of Carbon Sequestration using regression models in remote sensing in Berau, East Kalimantan, Indonesia” by Irvin K. Samalca, Alfred de Gier and Yousif Ali Hussin, of the Department of Natural Resources at The International Institute for Geoinformation Science and Earth Observation confirms and shows that 50% plus of a tropical tree’s woody biomass is carbon. That means that fast growing tropical trees like those planted by CO2 Tropical Trees and Amazonia Reforestation, which reach maturity in just 10 years, are excellent carbon storage vessels.

Dexter Dombro observing biomass increase in 11 month old Eucalyptus trees
Let’s calculate this from a different perspective. We know from several studies  that the woody biomass of a tropical tree plantation can increase by at least 35 cubic meters plus (14,382 board feet) per hectare per year. Depending on the hardwood species, one cubic meter (424 board feet) of tropical hard wood can weigh from 600 kg to 1,200 kg (1,322 lbs to 2,645 lbs). Assuming 1 hectare of trees with a gain of 35 cubic meters of wood times a conservative average of 750 kg (1,653 lbs) per cubic meter, and you get 26,250 kg (57,871 lbs) per hectare per year. If at least half of that woody biomass is carbon, then one gets 13,125 kg (28,935 lbs) of carbon. Divide 13,125 kg of carbon by an average of 600 mature plantation trees (after culls) and one gets 22.6 kg (50 lbs) per tree, the number used by CO2 Tropical Trees.

View of natural tropical forest canopy absorbing carbon
Why conservative? There is ample scientific support for much higher carbon sequestration rates by tropical trees. For example, Reforest the Tropics is an applied research program in Costa Rica demonstrating climate change mitigation through sustainable farm forestry. Using a 40 year base line they suggest that a natural tropical forest can sequester between 100 US tons to 160 US tons of carbon per acre (90.7 metric tons to 145 metric tons). This translates into 224 metric tons to 356 metric tons per hectare stored in a natural tropical forest over 40 years. Their research also suggests that a managed plantation of tropical trees will store as much as 800 US tons of CO2 per acre (725 metric tons). That translates into 1,792 metric tons per hectare. If one were to take 1,792,000 kg and divide by 40 years and then divide again by 1,250 tropical trees planted per hectare one would get 35.85 kg (79 lbs) per tree per year.

CO2 Tropical Trees bumber stickers are on cars all over the world!
CO2 Tropical Trees is actually relying on the most conservative estimates of carbon sequestration for its carbon neutral program. They are not alone in relying on those numbers. For example, Carbonify has a carbon calculator that is based on 22.6 kg or 50 lbs of carbon per tropical tree per year. Another example is the article by James Post, citing a 2005 study in Wikipedia that uses 22.6 kg or 50 lbs of carbon sequestration per tropical tree per year for the purpose of calculating carbon offsets. In conclusion all I can say is that every time someone funds the planting of a tropical tree with CO2 Tropical Trees or with Amazonia Reforestation, the very least they can expect from that tree is 22.6 kg or 50 lbs of carbon sequestered per year from our atmosphere. Given these facts and numbers people and institutions really don’t have any more excuses for not funding tree planting as an obvious partial solution to climate change.

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