This groundbreaking study provided high-resolution satellite imagery using a deep-learning algorithm. The study has found that there are at least 1.8 billion trees in the Sahel and Sahara deserts.
The study was conducted by a team of 24 scientists across Europe, the USA and Africa. The scientists discovered that the hitherto-called sub-humid zone is surprisingly filled with plant life, forcing a rethink of two of the world’s major deserts and even public policy on deforestation. Martin Brandt, an assistant professor of geography at the University of Copenhagen, who was the lead author of the research, said: “We were very surprised that there are quite so many trees growing in the Sahara desert”.
“Certainly there are vast areas without any trees, but there are still areas with a high tree density, and even between the sandy dunes, there are here and there some trees growing.”
The study was able to provide 11,000 high-resolution satellite images, spanning 1.3 million square kilometres (around 500,000 square miles), using a deep-learning algorithm that Brandt himself had to train by, individually counting and labelling some 90,000 trees, in a process that took him an entire year.
“The level of detail is very high and the model needs to know how all kinds of different trees in different landscapes look,” he said. “I didn’t accept misclassifications and further added training when I saw wrongly classified trees.”
The final count was completed within hours thanks to the powerful algorithm. It contradicts previous studies, which were based on estimates and extrapolations, and mapped close to zero-per cent tree cover. In contrast, Brandt’s highly detailed, painstaking counting of individual trees revealed a density of 13.4 per hectare.
The research also noted that not all trees in the areas are covered, as it limited counting to only those with an average crown size of 12 square meters.