High-resolution global map of smallholder and industrial closed-canopy oil palm plantations
Authors: Descals Adrià , Wich Serge , Meijaard Erik , Gaveau David L. A. , Peedell Stephen , Szantoi Zoltan 
Published: March 2021

Abstract. Oil seed crops, especially oil palm, are among the most
rapidly expanding agricultural land uses, and their expansion is known to
cause significant environmental damage. Accordingly, these crops often
feature in public and policy debates which are hampered or biased by a lack
of accurate information on environmental impacts. In particular, the lack of
accurate global crop maps remains a concern. Recent advances in deep-learning and remotely sensed data access make it possible to address this
gap. We present a map of closed-canopy oil palm (Elaeis guineensis) plantations by typology
(industrial versus smallholder plantations) at the global scale and with
unprecedented detail (10 m resolution) for the year 2019. The
DeepLabv3+ model, a convolutional neural network (CNN) for semantic
segmentation, was trained to classify Sentinel-1 and Sentinel-2 images onto
an oil palm land cover map. The characteristic backscatter response of
closed-canopy oil palm stands in Sentinel-1 and the ability of CNN to learn
spatial patterns, such as the harvest road networks, allowed the distinction
between industrial and smallholder plantations globally (overall accuracy =98.52±0.20 %), outperforming the accuracy of existing regional
oil palm datasets that used conventional machine-learning algorithms. The
user's accuracy, reflecting commission error, in industrial and smallholders
was 88.22 ± 2.73 % and 76.56 ± 4.53 %, and the producer's accuracy,
reflecting omission error, was 75.78 ± 3.55 % and 86.92 ± 5.12 %, respectively. The global oil palm layer reveals that
closed-canopy oil palm plantations are found in 49 countries, covering a
mapped area of 19.60 Mha; the area estimate was 21.00 ± 0.42 Mha (72.7 %
industrial and 27.3 % smallholder plantations). Southeast Asia ranks as
the main producing region with an oil palm area estimate of 18.69 ± 0.33 Mha or 89 % of global closed-canopy plantations. Our analysis
confirms significant regional variation in the ratio of industrial versus
smallholder growers, but it also confirms that, from a typical land development
perspective, large areas of legally defined smallholder oil palm resemble
industrial-scale plantings. Since our study identified only closed-canopy
oil palm stands, our area estimate was lower than the harvested area
reported by the Food and Agriculture Organization (FAO), particularly in West Africa, due to the omission of
young and sparse oil palm stands, oil palm in nonhomogeneous settings, and
semi-wild oil palm plantations. An accurate global map of planted oil palm
can help to shape the ongoing debate about the environmental impacts of oil
seed crop expansion, especially if other crops can be mapped to the same
level of accuracy. As our model can be regularly rerun as new images become
available, it can be used to monitor the expansion of the crop in
monocultural settings. The global oil palm layer for the second half of 2019 at a spatial resolution of 10 m can be found at https://doi.org/10.5281/zenodo.4473715 (Descals et al.,
2021).