Scientists from the CNRS and the universities of Orléans and Toulouse have developed a system capable of assessing the health of forest areas using satellite images.
We could already track the disappearance of the Amazon on Google Earth, and soon scientists could track a much more insidious phenomenon year after year: the slow decline of France’s forests. Due to repeated droughts linked to the climate crisis, the latter are in poor condition. However, it remains difficult to say to what extent.
Taking measurements directly in the field is a very expensive and time-consuming process due to the huge areas that need to be covered. This is why a team led by researcher Florian Mouret developed a method for satellite tracking tree health in Centre-Val de Loire. The fruits of their research, accompanied the Sycamore programwere published Institute of Electrical and Electronic Engineers.
The research was conducted by the company Center for the Spatial Study of the Biosphere (CESBIO) Toulouseattached to the CNRS, and through Laboratory of Physiology, Ecology and the Environment from Orléans.
This study should make it possible to better monitor the alarming forest loss on a national scale for several years. According to IGN, which published an extensive inventory of forest health in October 2023, tree mortality increased by 80% between 2013–2021 and 2005–2013. “In relation to the total volume of living trees, this phenomenon represents 0.5% of the total volume of trees”, warns the National Geographic Institute.
4⃣ Increase in tree mortality
Almost 80% increase in tree mortality for 2013-2021 compared to 2005-2013. In relation to the volume of living trees, this phenomenon represents 0.5% of the total volume of trees. pic.twitter.com/AD2K0yyQC6— IGN France (@IGNFrance) October 16, 2023
What do we call a “dying” forest? “We relied on the IGN definition” explains Florian Mouret.A tree is declared dying when more than 50% of its crown is lost.”, the upper part of its leaves.”An area is considered declining when 20% of the trees are dead or dying. This is a phenomenon that can be very diffuse.”
In other words, you can walk through the forest in Sologne without realizing that much of the trees around you are already giving up the ghost. This is where technology comes in, with the help of satellites and artificial intelligence.
The researchers used an artificial intelligence model that is able to take in large amounts of data and learn from it (this is called “machine learning”). This model was “fed” by two sets of data: on the one hand, field surveys, used as reference data, and on the other hand, satellite images in both the visible and infrared spectrum. Hence, as Florian Mouret summarizes, “the model learns to recognize healthy examples and examples considered to be in decline”.
Infrared images have been particularly useful to researchers. This spectrum of lightit allows us to capture information about the water content of the canopy”, explains the researcher.However, as far as we know, it is this water content that is the most discriminating when trees die.”In other words, the loss of oaks is directly related to drought, even though this tree is known to be very resistant to water shortages. Accurate satellite images, spread over several years, would therefore allow conclusions to be drawn about the state’s general forest health.
This health condition is not really in good condition. “We are witnessing a relatively rapid development of dying”, diagnoses Florian Mouret. A phenomenon that judges “quite disturbing”, joins IGN’s latest news on the subject.”Overall, it confirms what we already knew. Repeated drought between 2018 and 2022 intensified this phenomenon.”
A transformed test therefore for Florian Mouret and his laboratory. “The method proved to work well”, with an accuracy of 80% for oaks, the researcher estimates.
However, there is still room for improvement and the process remains “quite difficult”. But it should ultimately make it possible to more effectively measure the effects of global warming.
The project shows the scale of ongoing change, which is not easy to grasp on a daily basis. It also shows the extent of what remains to be done
Florian Mouret, researcher
How to overcome the climate crisis? “I remain an optimist, we must not let ourselves be defeated”, estimates the researcher. In fact, scientists have been equipping themselves for years with the tools to accurately confirm and monitor the climate crisis and the collapse of biodiversity. All that remains is for public authorities to act.