Sunday, July 11, 2010

How much carbon does a tropical tree sequester? (Part 1)

Dexter Dombro at experimental native tree plantation
Some people have asked me what evidence there is to support the claim by CO2 Tropical Trees that the average tropical tree will sequester 22.6 kg or 50 lbs of carbon per year. First off, let me stress that this is affected by location, soil type, rainfall and species. Having said that, most tropical trees located within 15 degrees northern and southern latitude of the equator do indeed sequester significant amounts of carbon dioxide (CO2) from the atmosphere, something that is supported by numerous studies and ongoing research. In this 2-part article I will offer some calculations in support of the efficiency of tropical plantation trees as a method of carbon sequestration. I will base my calculations on industry standard hectares (an area measuring 100 meters by 100 meters, or 2.47 acres) with 1,250 trees planted per hectare, later culled back to 600 trees per hectare.

Dexter Dombro with 11 month old tropical tree plantation
In an article entitled “Carbon sequestration in tropical agroforestry systems”, Alain Albrecht and Serigne T. Kandji of the Institut de Recherche pour le Développement found that the carbon sequestration potential of tropical agroforestry systems produced a median sequestration value of 95 metric tons (104 US tons) per hectare per year. Taking into account the variables of location, soil type, rainfall and species it can be as high as 228 metric tons (251 US tons) per hectare. Assuming a median of 95,000 kg divided by 1,250 trees per hectare one would get 76 kg (167 lbs) per tree. In a managed plantation trees are often culled back to about 600 trees per hectare, which would result in 158 kg (348 lbs) per tree per year. These numbers support the cubic meter increase of woody biomass observed in growing locations with excellent conditions. Please note that managed plantations generally produce 20 to 30 times more wood than do natural forests, resulting in higher carbon sequestration rates per hectare.

Natural tropical forest is less dense than plantation forests
Studies cited in Science Daily show that natural African tropical forests absorb about 600 kg (1,323 lbs) of carbon per hectare per year. If you take 600 kg by 25 times more wood per hectare in a plantation setting, you get 15,000 kg (33,000 lbs) per hectare per year divided by 600 plantation trees per hectare, which results in 25 kg (55 lbs) of carbon sequestered per tree per year. I should also mention that one of the species CO2 Tropical Trees plants is Acacia mangium, a recognized nitrogen-fixing tree (NFT). Studies like “Greater Soil Carbon Sequestration under Nitrogen-fixing Trees Compared with Eucalyptus Species” published by Ecosystems, a Springer publication, show that NFT’s sequester more carbon in the soil than do other types of tropical trees.

Dilmun Dombro admiring rapid growth of 2 year old Acacia mangium
One problem in the literature is the vastly varying time-lines on which research has been based. Both Amazonia Reforestation and CO2 Tropical Trees rely on a 10 year cycle from seed to mature tree for all of their calculations. This fact further enhances their credibility on the issue, because in the study “Carbon sequestration through afforestation: Role of tropical industrial plantations” their methodology of using a 10 year cycle to maximize woody biomass growth and carbon sequestration is supported. The article confirms that once tropical trees reach maturity their effectiveness for carbon sequestration purposes declines. That means that using a 10 year cycle maximizes the carbon sequestration efficiency of their tropical tree plantations. This analysis of studies and methodologies will continue in Part 2 of this article (next Post).

5 comments:

  1. Thank you Dexter - I was preparing some research for my masters course on whether international carbon payments could compensate for lost forest uses and found all these sources very useful. It's such a convoluted world out there in carbon valuation, this helped a lot.

    Keep up the good work!

    Nick

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