Vast stretches of previously undocumented forest have been discovered using a new tool to analyse the surface of the Earth.

International researchers have discovered 467 million hectares, an area equivalent to 60 per cent of the size of Australia, of what was previously considered dry land is actually dense forest.

The research led by the Food and Agriculture Organisation of the United Nations, teams of scientists and students from 15 organisations, including the University of Adelaide, carried out the analysis using the photo-interpretation tool called Collect Earth.

Photo: A Baobab forest in Senegal, a few kilometres from Dakar. (Supplied: FAO/Faidutti)