Carbon Stocks
Aboveground forest biomass is the most vulnerable carbon stock in relation to slash and burn agriculture and deforestation (Kotto-Same et. al., 1997). Tschakert, Coomes, and Potvin (2005) demonstrated the clear correlation between trees of width 10-99 cm and the total carbon in a system. Based on this, it is clear that slash and burn agriculture greatly depletes the carbon stock of a given forest, because clearing and burning trees depletes on of the most important pools of carbon.
This graph demonstrates that trees, when present, store the most carbon of all aboveground biomass. They are also the most vulnerable to slash and burn agriculture as is demonstrated by their absence on the left side of the graph. Click on the image to enlarge it.
(Tschakert et. al., 2005)
The actual estimates of how much carbon is stored in or released from each hectare of forested or deforested land vary depending on the forest. Fearnside (1998) found that in 1990, 254 million tons of carbon were released from 1.38 million hectares of cleared forest in the Brazilian Amazon. That comes out to an average of 184 t C/ha. He also noted that the amount of carbon per hectare of land after deforestation depends greatly on the land use. Fearnside claimed that IPCC estimates of 5 t C/ha of replacement land were too low and that the average number would be closer to 12.8 t C/ha. This was still a very significant loss of carbon compared to the forest stock (Fearnside, 1998). Loarie, Asner, and Field (2009) found that an average of 183 t C were released per hectare in the Brazilian Amazon in 2001. They also found that as deforestation encroaches into more biomass rich northern areas of the Amazon, the carbon stored per hectare of forest goes up. The rate at which carbon was lost in 2007 was up to 201 t C/ha (Loarie et. al., 2009). A study in Cameroon by Kotto-Same, Woomer, Appolinaire, and Louis (1997) found that there were 300 t C/ha of forest and that 220 t C/ha were lost due to deforestation. The majority of this loss (204 t C/ha) came from aboveground biomass (Kotto-Same et. al., 1997).
The estimates of Soil Organic Carbon (SOC) losses are less clear. A study of a deciduous forest in Mexico by Garcia-Oliva, Sanford, and Kelly found that soil carbon concentrations in pastures were 31% lower than those of the forest at 0-2 cm, and 28 % lower at 2-5 cm (Garcia-Oliva et. al., 1998). Estimates of losses of SOC range from 21 t C/ha in Thailand to 15 t C/ha in Sri Lanka to 8 t C/ha in Mozambique (Kotto-Same et. al., 1997). A summary of other studies suggested that 20-30% of SOC in the top 1m of soil is lost in one cycle of slash and burn agriculture (Houghton et. al., as cited in Tinker et. al., 1996). The authors cite that estimates of this loss are about 6-9 t C/ha emitted into the atmosphere, but pointed out that data in this area was not clear and required further research comparing SOC of forests and replacement land uses.
Carbon Dioxide (Carbon) Emissions
Deforestation plays an important role in global anthropogenic carbon dioxide emissions. The Intergovernmental Panel on Climate Change ([IPCC], 2007) reports that 5.8 Gt of CO2 were released each year in the 1990’s as a result of deforestation. If current deforestation rates continue (a business as usual scenario), the IPCC (2007) estimates that 40% of the current 540 million hectares of the Amazon will be deforested by 2050, causing emissions of 117,000 ± 30,000 Mt CO2 to the atmosphere.
This graph by the IPCC (2007) shows the role of deforestation in global greenhouse gas emissions alongside other contributors. Deforestation accounts for about 17.3% of global anthropogenic GHG emissions. Click on the image to enlarge it.
