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African forests store 25% of tropical forest carbon

Sign warning that a rainforest tree has been spiked to discourage illegal logging in Indonesian Borneo


Forests in sub-Saharan Africa account for roughly a quarter of total tropical forest carbon, according to a comprehensive assessment of the world’s carbon stocks published in the journal Proceedings of the National Academy of Sciences (PNAS).



The study, based on remote sensing data and field surveys of 75 calibration plots, came up with estimates of forest cover and carbon storage based on varying definitions of what constitutes forest. Using the broadest definition of 10 percent tree cover, forests cover 775 million hectares, or 36 percent, of sub-Saharan Africa. Using a 30 percent tree cover cutoff, sub-Saharan Africa’s forest extent amounts to 447 million hectares, or 21 percent.



The researchers estimate sub-Saharan Africa’s forests contain 44-66 billion tons of carbon, depending on how forests are defined. Nearly 80 percent of the carbon is stored in aboveground biomass or vegetation consisting of leaves, branches, and tree trunks.


Unlike other tropical forest regions, nearly three-quarters of Africa’s forests are distributed in woodland savannas and dry forests that contain less than 100 tons of carbon per hectare. Extremely carbon-dense forests, which store more than 350 tons of carbon in aboveground biomass per hectare, account for 8.7 percent of sub-Saharan Africa’s total stored carbon.



Overall, African forests store the least amount of carbon per hectare of any region, averaging 69-117 tons per hectare. Asia is the highest, averaging 125-174 tons per hectare per hectare, followed by the tropical Americas, which averages 87-132 tons per hectare.



Unsurprisingly, the forests of the Democratic Republic of Congo are the most extensive and store the most carbon of any African country, accounting for 26-37 percent of forest cover (depending on how forest is defined) and 38-56 percent of carbon. Three other Congo Basin countries — Cameroon, Republic of Congo, and Central African Republic — follow.



The new carbon data indicate that deforestation in Africa produces proportionately fewer emissions than estimated by the Food and Agriculture Organization of the United Nations (FAO).



FAO estimates are based on the assumption that African forests store one-third of tropical forest carbon and accounted for 30 percent of deforestation between 2000 and 2005. By comparison, the PNAS study, combined with remote sensing work by Matt Hansen of South Dakota State University, which put Africa’s share of tropical deforestation at less than 6 percent from 2000-2005, suggests that Africa’s forest loss is a considerably smaller driver of climate change than conventionally thought.



CITATION: Sassan Saatchi et al (2011). Benchmark map of forest carbon stocks in tropical regions across three continents.” PNAS June 3, 2011.




Mean biomass estimate for sub-Saharan African nations using a 25% forest cover definition

Country Forest Area
(mln ha)
Aboveground forest carbon stocks
(Mt C)
Belowground forest carbon stocks
(Mt C)
Total forest carbon stocks
(Mt C)
Avg Carbon Density
(t C/ha)
Angola 50 1,792 547 2,339 47
Benin 0 6 2 8 29
Botswana 1 12 4 16 19
Burundi 0 15 4 19 64
Cameroon 30 3,361 906 4,268 142
Central
African
Republic
42 2,145 631 2,776 66
Chad 1 20 6 26 31
Côte d’Ivoire 6 406 116 522 85
DR Congo 177 17,805 4,857 22,662 128
Equatorial
Guinea
2 310 82 393 160
Ethiopia 13 536 161 698 53
Gabon 22 2,820 748 3,568 164
Gambia 0.04 0.3 0.1 0.4 12
Ghana 3 225 63 288 94
Guinea 8 365 109 473 57
Guinea-Bissau 1 38 12 50 37
Kenya 2 86 26 111 54
Lesotho 1 13 4 17 19
Liberia 9 990 266 1,257 147
Madagascar 17 893 261 1,154 70
Malawi 2 51 16 67 40
Mali 0.28 9 3 12 44
Mozambique 35 1,124 348 1,472 42
Namibia 0.05 1 0.2 1 16
Nigeria 7 450 129 579 83
Rep. of Congo 24 3,015 802 3,817 160
Rwanda 0.33 19 5 24 73
Senegal 1 11 4 14 26
Sierra Leone 5 299 86 385 83
Somalia 0 2 1 2 34
South Africa 10 217 70 288 28
Sudan 13 433 133 567 45
Swaziland 0.49 12 4 16 32
Tanzania 17 585 179 764 45
Togo 0.19 7 2 9 49
Uganda 4 188 55 244 65
Zambia 31 1,027 317 1,344 43
Zimbabwe 6 128 41 170 30







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