Dryland biological areas cover two-fifths of Earth’s land surface, but the forest cover in these areas is poorly known. A global initiative to undertake a Global Drylands Assessment of forest was formed. To determine the extent of forests and tree cover throughout the world’s dryland areas, a large number of very high resolution images available from Google Earth were analyzed. A crowd-sourcing approach was adopted to visually interpret the images covering 213,795 forest plots. To do this the world’s dryland domain was divided into 12 regions and scientists and students around the world were trained to use a an interpretation tool called Collect Earth to assess the dryland forest plots in which they had expertise. It was found that in 2015, 1,327 million hectares of drylands had more than 10% tree-cover, of which 1,079 million hectares comprised forest according to the accepted definition of forest. This estimate is 40 to 47% higher than previous estimates and increases current estimates of global forest cover by at least 9%.