High-resolution satellite imagery has been used to map every single tree in Africa, demonstrating a technique that could help improve the monitoring of deforestation across the world.
Florian Reiner at the University of Copenhagen, Denmark, and his colleagues used images from satellites operated by US firm Planet and machine-learning models to map canopy cover across the entire African continent.
Modern satellites usually capture tree canopies at a resolution of 30 metres – fine for measuring the size of forests, but less good at mapping individual trees and small thickets.
The satellite data Reiner and his colleagues used had a resolution of 3 metres, enabling the study to map all trees, including those not part of a forest.
The results suggest that 30 per cent of all trees in Africa aren’t in a forest, and instead are scattered across farmland, savannah and urban areas.
Many countries in Africa lack dense forests, but have a lot of trees nonetheless, says Reiner. “These trees are incredibly important to the local ecosystems, the people, to the economy.”
Similar research has also been done mapping canopy cover across Europe, which reveals that, in some countries, up to 24 per cent of tree cover is found outside forests.
By tracking every single tree or thicket, researchers can start to monitor how these trees are coping with climate change, says Reiner, or whether they are vulnerable to deforestation. It could also improve the monitoring of reforestation efforts, which are growing in popularity as a way of removing carbon dioxide from the atmosphere.
“At a local level, being able to consistently monitor when and where trees are disappearing or reappearing can generate more actionable insights,” says John Francis at the Alan Turing Institute in London.
The study is a proof of concept rather than a map ready for immediate commercial use, says Reiner. “It’s research work. it’s showing what could be done,” he says.
But he is already working with colleagues to scale up the tracking approach to cover the entire global canopy: “We’re hoping that this will be seen as a way forward in monitoring tree resources.”