A new study finds oil palm plantations store less carbon than previously believed, suggesting that palm oil produced through the conversion of tropical forests carries a substantial carbon debt.
The study, conducted at two sites in Sumatra and Kalimantan by scientists at the World Agroforestry Centre (ICRAF), found that mature oil palm plantations store less than 40 tons of above-ground biomass on average over their 25-year lifespan. By comparison logged-over forests at the two sites stored 70-200 tons of carbon per hectare. Untouched forest contains even more carbon, sometimes in excess of 400 tons per hectare.
The finding that oil palm plantations store less carbon than natural forest are not a surprise, but the new figure is lower than earlier estimates. Other research has shown that palm oil produced from plantations grown in place of tropical forests incur a “carbon payback time” of decades to centuries. Carbon payback time refers to the number of years it takes for the emissions saved by the replacement of fossil fuels with biofuel to offset the carbon emissions generated when the land is converted for growing the biofuel feedstock. Since oil palm plantations are typically planted on a 25-year cycle, a carbon payback time exceeding 25 years makes palm-oil biodiesel a larger source of emissions than conventional petroleum. But payback times are considerably lower when plantations are established on grasslands and abandoned, non-forest agricultural land, where the amount of carbon stored is significantly less than in forest vegetation. Under such circumstances, palm oil can have one of the lowest carbon payback times, owing to its high productivity.
 (1)Time series land cover map of site 2 estate from the study and (2) time averaged carbon-stock of oil palm at plot level. Courtesy of the authors. Click image to enlarge |
Accordingly, the authors of the ICRAF study recommend that conversion should be limited to shrub and grassland areas where aboveground carbon stock is less than 40 tons per hectare. Areas with higher carbon stock should be set aside in conservation areas, allowing the forest to re-generate where it has been degraded by logging. Companies that employ this strategy may benefit from payments under REDD, a proposed climate change mitigation mechanism that would pay developing countries for avoiding emissions from deforestation. Already some plantation companies have shown interest in the concept. Last month Sinar Mas and First Borneo Group agreed to forgo conversion of peat forest in West Kalimantan on the island of Borneo in exchange for carbon payments. By some estimates, REDD could make conservation of high carbon ecosystems profitable relative to other forms of land use.
Deforestation accounts from nearly 20 percent of greenhouse gas emissions from human activities. Forest clearing and degradation of carbon-rich peatlands are the primary reason Indonesia ranks as the world’s third largest emitter of greenhouse gases despite having limited industrial activity.
Dr Meine van Noordwijk, Dr Sonya Dewi, and Suseno Budidarsono. Carbon Footprint of Indonesian Palm Oil Production: a pilot study. World Agroforestry Centre (ICRAF) July 2009.
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