African trees in the dusk

Pop quiz: How many trees are there in West Africa?

This is Sandra Tsing Loh with the Loh Down on Science.

Martin Brandt from University of Copenhagen wondered. So with the aid of NASA and an international team, he built a computer program to count trees — using machine learning!

Just like teaching your dog to sit, teaching a COMPUTER takes training. The program studied over eighty-nine thousand satellite photos of West Africa. Is that a tree, a patch of grass, or a giraffe? From those, it learned to spot the trees and tally them up. The more the program learned, the more areas it was tested on.

So, how many trees did YOU guess?

Would you believe nearly. . . TWO BILLION? That’s WAY more than scientists previously estimated–and much more accurate than previous methods! Humans verified the photos, so we know the count is accurate.

Now scientists can map the location and size of trees all over the world. Mapping helps track the health of tree populations and the effects of climate change.

Next? Instead of GPS, TREE-P-S!

Instead of MapQuest, how bout SapQuest? Sorry!

Brandt, M., Tucker, C.J., Kariryaa, A. et al. An unexpectedly large count of trees in the West African Sahara and Sahel. Nature (2020).