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Yu Le’s Research Group of the Department of Earth System Science (DESS), Tsinghua University, in collaboration with several research groups at home and abroad such as Li Wei’s Research Group, using high-resolution biomass data and datasets of the change of the areas of oil palm plantations, has recently estimated forest biomass loss during 2001–2015 caused by oil palm encroachment, and discovered that the encroachment of oil palm plantations from low to high biomass density forests after 2007.

Oil palm expansion, as one of the important drivers of deforestation in tropical areas, threatens tropical forests and their ecosystem services (such as carbon sequestration). However, refined spatio-temporal dynamic analysis is lacking in the study on the impact of oil palm expansion and encroachment on forest on regional carbon storage. Present research mainly estimates the changes in regional carbon storage caused by oil palm expansion based on the biomass data obtained from field observation and the changes in areas of oil palm, with little consideration of spatial differences. Therefore, there is still great uncertainty in the estimation of ecosystem carbon storage changes caused by oil palm expansion.

To address the above problems, the Research Group, based on the previously published distribution data of oil palm plantations in Malaysia and Indonesia (https://www.earth-syst-sci-data.net/12/847/2020/essd-12-847-2020.html), and in the light of the global aboveground biomass data in 2010 (GlobBiomass2010), employed the research method of spatial sequence instead of time, the temporal and spatial distribution of vegetation carbon storage changes caused by oil palm encroachment on forests in Malaysia and Indonesia from 2001 to 2015 was revealed, and the relationship between oil palm plantation scale and carbon density changes was analyzed.

During 2001–2015. the expansion of oil palm in the region under study into forests caused a forest biomass loss of 50.2 ± 21.9 TgC (Fig. 1). The area expansion of large industrial oil palm plantations and the total carbon loss caused by them were the highest. If the forest biomass loss caused by the expansion of oil palm plantations, the biomass increase caused by the growth of oil palm, the biomass decrease of marginal forest caused by the expansion of oil palm and the soil carbon loss before and after the expansion were taken into consideration comprehensively, the total carbon loss in the study period amounted to as high as 1063.7±409.6 TgC. During 2001-2015, the land use transformation of oil palm plantations came more from secondary forests than from primary forests used in traditional estimation methods. After 2007, oil palm plantations gradually shifted from encroaching on forests with low carbon density to encroaching on forests with high carbon density. This trend was the most obvious in small oil palm plantations owned by small farmers (Fig.1d).

The area of oil palm expansion and encroachment on forests and the corresponding loss of forest biomass in protected areas (PA) were further analyzed. It was found that the phenomenon of oil palm expansion and encroachment on forest occurred in 395 PAs in Indonesia and Malaysia. From 2001 to 2015, the planting area of oil palm in nature reserves increased continuously (from 0.03 to 0.12 million hectares), and the proportion of forest biomass loss caused by oil palm expansion inside and outside the nature reserve increased from 0.7% to 1.5%.

The research has confirmed the importance of oil palm expansion in regional land use change carbon emissions, pointing out that policy makers should develop more effective policies to prevent oil palm from expanding and encroaching on forests or PAs with high carbon reserves.

Fig. 1 Forest biomass loss caused by oil palm expansion

The results of above research were published online in Nature Sustainability on April 14th, 2022 in a paper titled "Recent expansion of oil palm plantations into carbon-rich forests".

Xu Yidi, a graduate of DESS, Tsinghua University, is the first author of the paper; Associate Professor Yu Le and Associate Professor Li Wei of DESS, Tsinghua University are the co-authors of the paper. The collaborators include Prof. Philippe Ciais of Laboratoire des Sciences du Climat et de l’Environnement (LSCE), Dr. Maurizio Santoro of Gamma Remote Sensing Company, Dr. Yang Hui of Max Planck Institute of Biogeochemistry and Prof. Gong Peng of the University of Hong Kong. This research has been supported by the National Key R&D Program, the Independent Research Program of Tsinghua University and the National Key Scientific and Technological Infrastructure Projects.

Full-text link: https://www.nature.com/articles/s41893-022-00872-1

Since 2015, several research groups of DESS, Tsinghua University, in collaboration with Prof. Arthur Cracknell of the University of Dundee, UK, have conducted in-depth research focusing on global oil palm mapping and ecological effects of the oil palm planting industry, and have achieved a series of research results, including multi-resolution remote sensing image recognition using machine learning and deep learning algorithms, forming multi-year oil palm mapping products of global and regional scales. The expansion mode of oil palm plantations and the rapid monitoring of oil palm growth have been realized. In light of the biodiversity and biomass data, the influence of oil palm expansion on sustainable development has been revealed. Prof. Arthur Cracknell passed away on April 21, 2021, and the research group expressed deep mourning for Prof. Cracknell.

Related papers:

Cheng, Y., Yu, L., Cracknell, A. P., & Gong, P. (2016). Oil palm mapping using Landsat and PALSAR: A case study in Malaysia. International journal of remote sensing, 37(22), 5431–5442. https://doi.org/10.1080/01431161.2016.1241448

Du, Z., Yu, L., Yang, J., Xu, Y., Chen, B., Peng, S., Zhang, T., Fu, H., Harris, N., & Gong, P. (2022). A global map of planting years of plantations. Scientific Data, 9(1), 141. https://doi.org/10.1038/s41597-022-01260-2

Li, W., Fu, H., Yu, L., & Cracknell, A. (2017). Deep Learning Based Oil Palm Tree Detection and Counting for High-Resolution Remote Sensing Images. Remote Sensing, 9(1), 22. https://doi.org/10.3390/rs9010022

Xu, Y., Ciais, P., Yu, L., Li, W., Chen, X., Zhang, H., Yue, C., Kanniah, K., Cracknell, A. P., & Gong, P. (2021). Oil palm modelling in the global land surface model ORCHIDEE-MICT. Geoscientific Model Development, 14(7), 4573–4592. https://doi.org/10.5194/gmd-14-4573-2021

Yu, L., Cao, Y., Cheng, Y., Zhao, Q., Xu, Y., Kanniah, K., Lu, H., Yang, R., & Gong, P. (2022). A study of the serious conflicts between oil palm expansion and biodiversity conservation using high-resolution remote sensing. Remote Sensing Letters, 0(0), 1–15. https://doi.org/10.1080/2150704X.2022.2063701

Written by: Xu Yidi, Du Zhenrong, and Yu Le

Abstract I

Yu Le’s Research Group of the Department of Earth System Science (DESS), Tsinghua University, in collaboration with several research groups at home and abroad such as Li Wei’s Research Group, published a paper titled "Recent expansion of oil palm plantations into carbon-rich forests" online in Nature Sustainability on April 14th, 2022.

Abstract II

Yu Le’s Research Group of the Department of Earth System Science (DESS), Tsinghua University, in collaboration with several research groups at home and abroad such as Li Wei’s Research Group, using high-resolution biomass data and datasets of the change of the areas of oil palm plantations, has recently estimated forest biomass loss during 2001–2015 caused by oil palm encroachment, and discovered that the encroachment of oil palm plantations from low to high biomass density forests after 2007.

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