Extended Data Fig. 4: Overview of training sites and study area.

The study area for the wall-to-wall mapping is the westernmost part of the Sahara and Sahel. It represents a typical north–south ecological and climatic gradient, starting in the Sahara Desert in hyper-arid areas (rainfall of 0–150 mm yr−¹) with a sparse vegetation coverage, over arid (rainfall of 150–300 mm yr⁻¹) and semi-arid (rainfall of 300–600 mm yr⁻¹) Sahelian rangelands and croplands, up to sub-humid (rainfall of 600–1,000 mm yr⁻¹) Sudanian lands, where shrublands turn into forests. a, The locations of the manually drawn 89,899 tree crowns used for training the model are shown in red. CHIRPS rainfall⁴³ was used to delineate the rainfall zones. The land use for farmland and urban is from Copernicus Global Land²⁶. In situ data were collected at the field sites around Widou and Dahra in Senegal. Areas of insufficient data quality and beyond rainfall of 1,000 mm yr⁻¹ were masked. b, The region was analysed for sandy (>70% sand content) and non-sandy areas⁴⁴.