A new study in Indonesia shows that for oil palm plantations to claim carbon neutrality, they can only convert land with vegetation cover holding carbon stocks equivalent to 40 Mg C ha-1. This strongly disputes recent advice by a committee of experts who claimed that the acceptable limit is conversion of land with up to 75 Mg C ha-1 under a High Carbon Stocks+ scheme.
"This value of 75 is considerably higher than what has so far been considered and opens up opportunities to convert a range of secondary forest and agroforest vegetation types, and that is why we sought to find out if there is a scientific rationale for this value,” says Ni’matul Khasanah, lead author of the new study titled: Aboveground Carbon Stocks in Oil Palm Plantations and the Threshold for Carbon-Neutral Vegetation Conversion on Mineral Soils, published in Cogent Environmental Science.
The type of land, characterized by its aboveground carbon stock that can be converted into oil palm plantation has been widely discussed in terms of the ‘carbon debt’ incurred and the length of time needed to ‘repay’. The rapid expansion of oil palm plantations, the deforestation this causes and the options to rehabilitate degraded lands are related to a threshold value of what types of land can be used to avoid net accountable emissions of greenhouse gases (CO2).
“Based on study reviews, the appropriate time scale to make such a comparison is the ‘production life cycle’, that considers the fate of a plantation from initial planting till the end of economic life cycle and replanting. During this period the aboveground C stock (AGC) will increase – but its time-averaged value can be derived from measurements. Current estimates range from 36 Mg C ha-1to the said 75 Mg C ha-1,” explains Dr Meine van Noordwijk a co-author in the study.
Based on the largest data set available for Indonesian oil palm so far, the new study provides a threshold value for AGC derived from 180 measurement plots from 25 plantations stratified across all the major settings in which oil palm is found in Indonesia.
“Our study results showed that the time-averaged aboveground carbon stock of oil palm plantation ranges from 37.76 ± 0.33 Mg C ha-1 till 42.07 ± 0.03 Mg C ha-1. Soil type and plantation management are sources of variation around these values,” says Ni’matul Khasanah. The values include four Carbon pools: oil palm biomass, standing litter stock comprising pruned fronds, understorey vegetation, and preceding necromass stock (dead wood).
“Based on this evidence, we strongly propose that a value of 40 Mg C ha-1 in time-averaged AGC of oil palm plantation can be used as the threshold for aboveground carbon debt-free land conversion,” notes Harti Ningsih a co-author in the study.
A parallel study on the changes in soil carbon stock of oil palm plantations on mineral soils (peat is a very different story) concluded that if good management practice is followed there is no changes in mineral soil carbon stock of oil palm plantations derived from forest or non-forest in Indonesia. With these results, at plot level, conversion of land with 40 Mg C ha-1 in aboveground carbon stock into oil palm plantation is carbon neutral.
The new study clearly rejects the proposed 75 Mg C ha-1in AGC as a threshold for AGC of a land that can be converted to oil palm with a claim to be carbon neutral at plot level. Whether or not landscape-level compensation can justify use of the term ‘carbon neutral’ is open to debate.
Read journal article
Khasanah N, van Noordwijk M, Ningsih H. 2015. Aboveground Carbon Stocks in Oil Palm Plantations and the Threshold for Carbon-Neutral Vegetation Conversion on Mineral Soils. Cogent Environmental Science. 1: 1119964
Read Policy brief
van Noordwijk M, Khasanah N, Dewi S. 2015. When can oil palm production qualify for a ‘carbon neutral’ claim?. ASB Policy Brief 49. Nairobi. ASB Partnership for the Tropical Forest Margins.
Raison J, Atkinson P, Chave J, DeFries R, Joo GK, Joosten H, Navratil P, Siegert F. 2015. HCS+, A new pathway to sustainable oil palm development, Draft Extended Summary. http://www.carbonstockstudy.com/carbonstockstudy/files/f6/f63fcf9e-10e1-47f8-bfbd-3b9e01505cec.pdf, last accessed October 7, 2015.
Agus F, Gunarso P, Sahardjo BH, Harris N, van Noordwijk M, Killeen TJ. 2013b. Historical CO2 emissions from land use and land cover change from the oil palm industry in Indonesia, Malaysia and Papua New Guinea. In: T.J. Killeen & J. Goon (eds.) Reports from the Technical Panels of the Second Greenhouse Gas Working Group of the Roundtable for Sustainable Palm Oil (RSPO); RSPO, Kuala Lumpur. pp 65-88. http://www.rspo.org/file/GHGWG2/5_historical_CO2_emissions_Agus_et_al.pdf.