On a hill near Chiang Mai in northern Thailand, a drone fires up its propellers and rises above the forest to better understand its role in combating climate change.
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The device systematically flies over the dense jungle and sends hundreds of photos to the ground, which are then stitched together in 3D.
This technology allows scientists to quickly get an accurate picture of the state of the forest and estimate the amount of carbon it absorbs. In fact, trees are important sensors for CO2, the gas that contributes most to global warming.
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Their role is therefore crucial. However, according to the World Forest Observatory, forests have declined by 12% worldwide since 2000 due to deforestation.
But the size of the area is not the only criterion. The amount of CO2 absorbed by the forest varies depending on the tree species and age of the trees.
Define best practices
Without a drone, “we have to go through the entire forest with a pole and a 5-meter rope and take measurements on each tree,” explains Stephen Elliott, director of a forest restoration research unit (FORRU) at Chiang Mai University.
A gigantic task. And “20 students stomping around on the floor with tape measures and poles… that’s not good for the basement either.”
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Thanks to the drone, “you no longer enter the forest.”
Three measurements are required: height, circumference and density of the wood.
The machine follows a pre-programmed flight path while the team on the ground uses binoculars to look for possible obstacles such as a bird.
“We collect data or take pictures every three seconds,” explains Worayut Takaew, the drone pilot.
“The overlapping images are then converted into a 3D model that can be viewed from different angles.”
The goal of Stephen Elliott and his team is not large-scale reforestation, but rather defining good practices: planting native species, encouraging the return of animals that bring seeds of other species, and working with residents.
The replanting of the property, which began several decades ago, is a success that can be seen spectacularly in the 3D images compared to neighboring properties that were left intact and sparse.
According to Stephen Elliott, whose team also calculates the carbon stored by the leaf mat and humus, the plot stores as much carbon as a virgin forest.
The drone has a major flaw, it cannot clearly see what is happening under the treetops. To do this, scientists use LiDAR-type scanners, which enable high-resolution scanning of the entire forest at eye level.
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“It is possible to enter the forest and reconstruct the shape and size of each tree,” explains Emmanuel Paradis, a French researcher at the Research Institute for Development (IRD).
He is leading a multi-year project to produce the most accurate analysis yet of how much carbon Thailand's forests can store.
Precise measurements
Five forest types are mapped, including plots reforested by Stephen Elliott's teams using drone-mounted LiDAR radars.
“The aim is to obtain an estimate of the carbon storage capacity of forests across Thailand,” explains Emmanuel Paradis.
“Many people, and I somewhat agree, think that these estimates are not precise enough,” he says.
“Overly optimistic estimates can create too much hope and too much optimism about the potential of forests to store carbon,” he warned.
The urgency is driving rapid developments, including the launch next year of the European Space Agency's biomass satellite that will monitor carbon stocks in forests.
“Technology is evolving, satellites are becoming more and more precise… and statistical technologies are becoming more and more precise,” says the researcher.