Global mapping of oil palm planting year from 1990 to 2021

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Abstract. Oil palm is a controversial crop, primarily because it is associated with negative environmental impacts such as tropical deforestation. Mapping the crop and its characteristics, such as age, is crucial for informing public and policy discussions regarding these impacts. Oil palm has received substantial mapping efforts, but accurate and up-to-date oil palm maps of both extent and age are essential for monitoring impacts and informing concomitant debate. Here, we present a 10 m resolution global map of industrial and smallholder oil palm, developed using Sentinel-1 data for the years 2016–2021 and a deep learning model based on convolutional neural networks. In addition, we used Landsat-5, Landsat-7, and Landsat-8 to estimate the planting year from 1990 to 2021 at a 30 m spatial resolution. The planting year indicates the year of establishment of the current (as of 2021) oil palm plantation by means of either newly planted or replanted oil palm in an existing oil palm plantation. We validated the oil palm extent layer using 18 812 randomly distributed reference points. The accuracy of the planting-year layer was assessed using field data collected from 5831 industrial parcels and 1012 smallholder plantations distributed throughout the global oil palm growing area. We found oil palm plantations covering a total mapped area of 23.98 Mha, and our area estimates are 16.82 ± 0.19 Mha of industrial oil palm and 7.37 ± 0.25 Mha of smallholder oil palm worldwide. The producer's and user's accuracy are 91.0 ± 2.5 % and 91.8 ± 1.2 % for industrial plantations and 71.4 ± 0.7 % and 72.4 ± 1.8 % for smallholders; these values represent an improvement compared to a previous global oil palm dataset, particularly in terms of omission of oil palm. The overall mean error between the estimated planting year and the field data was −0.24 years, and the root-mean-square error was 2.65 years, but the agreement was lower for smallholders. Mapping the extent and planting year of smallholder plantations remains challenging, particularly for wild and sparsely planted oil palm, and future mapping efforts should focus on these specific types of plantations. The average oil palm plantation age was 14.1 years, and the area of oil palm over 20 years old was 6.28 Mha. Given that oil palm plantations are typically replanted after 25 years, our findings indicate that this area will require replanting within the coming decade, starting from 2021. Our dataset provides valuable input for optimal land use planning to meet the growing global demand for vegetable oils. The global oil palm extent layer for the year 2021 and the planting-year layer from 1990 to 2021 can be found at https://doi.org/10.5281/zenodo.13379129 (Descals, 2024a).