It releases a lot of carbon dioxide (CO2) that nature cannot capture, clear forests, build roads, exploit the land, use chemicals, fish more than the oceans allow… In each of its activities, humans interact with other ecosystems . But its excesses will result in the reduction of biodiversity. We even talked “sixth mass extinction”. Therefore, to compensate for these harmful effects, initiatives were born. This is the case of the Great Green Wall. Launched in 2007 by the African Union, this ecological restoration project plans to plant… millions of trees. What does it consist of? How does this happen on earth? Fifteen years after its launch, what are the results? Answers to episode 2 of “The Knowledge Factory, Season 2”, a podcast from world produced in collaboration with Espace Mendès-France in Poitiers.
At the microphone of the journalist Joséfa Lopez, Gilles Boëtsch, anthropologist, emeritus research director of the CNRS and co-director of the Hommes-Milieux Téssékéré observatory, Aliou Guissé, botanist, professor of plant ecology at the Cheikh-Anta-Diop University in Dakar (UCAD ) and co-director of the Hommes-Milieux Téssékéré observatory, and Martine Hossaert-McKey, emeritus research director of the CNRS at the ChimEco laboratory and the functional and evolutionary ecology center in Montpellier, biodiversity and overseas mission manager for the CNRS.
The Great Green Wall is an 8,000 kilometer reforestation project between Senegal and Djibouti. Why was it launched?
Gilles Boetsch: The Great Green Wall project aims to limit the advance of the desert in a vulnerable region located near the Sahara, the Sahel, in the grip of the desert. And that is by planting trees. This project fits the context and ecosystem of each country where it is developed. Senegal serves as a showcase, as does Mauritania at its level. But between the climate, the hordes and the armed conflicts, you must hold on to make this Great Wall grow!
Martine Hossaert-McKey: With the Great Green Wall, we can talk about an open-air laboratory experience! It is a kind of mosaic where each country takes over the project in its own way, depending on the culture, the soil, the texture of the soil. We will not plant the same trees in Senegal as in Mauritania or Ethiopia, for example…
How do you grow trees in desert areas?
Aliou Guisse : The choice of species is important. This is done on two criteria. First, the desires of the local population, whose opinion is asked. Then, in the list of species that emerged, we tested some of them in the laboratory. Finally, we kept seven, the most adapted or the most likely to adapt to a climate as bad as the Sahelian zone. Then we grow the plants in the nursery and when they reach a certain size, they are planted. This allows them to be a little autonomous vis-à-vis the water. We reforex during the winter to take advantage of the rainy season, which starts in August in the Sahelian zone, and we make furrows in the ground to trap rainwater.
How many trees have been planted since 2007?
UK: In Senegal, we have two million plants. But, be careful, not whole trees, we plant small trees, about half of them survive.
A.G : In other less hostile areas, you can go up to 68% success rate. If you have a serious follow-up, eco-guards will monitor and put up a fence to protect the plants.
Why do you need to replant more trees in these areas?
UK: In the past, people came to this place only during the rainy season, when there was water. Then they left. Today, these populations remain permanent because there are boreholes and they practice animal husbandry there. Animals roam and graze. Result: the Sahelian forest has lost 80% of its mass in a century. With the Great Green Wall, we are trying to restore the forest as it existed a century ago. But the pressure of cattle made things very difficult.
A.G : It is difficult to convince people to reduce livestock farming, because it is a tradition and an honor for the Fulani to have as many cattle as possible.
In addition to stopping desertification, the Great Green Wall has a socio-ecological purpose. It aims to improve the living conditions and health of the population, to fight food insecurity, against poverty…
MH-M. : This is an excellent example of a nature-based solution, as planting trees helps regenerate forests and restore biodiversity. The tree also allows weeds to settle down, it attracts new pollinators, insects. People can reuse some plants for their consumption, for fodder…
UK: The Great Green Wall also improves the health of the population. In fact, in some countries, 30% of the population suffers from respiratory diseases due to desert dust. However, if we can moisten the soil more thanks to the trees, this will cause the dust to fall. Therefore respiratory diseases are reduced.
What is the reaction of the guardians to the construction of the Great Green Wall?
GA: At first, everyone thought that this green wall would be compact, like a kind of waterproof strip of trees. We made arrangements to let the crowds pass. Today’s herders realize that they derive many benefits from reforested plots. For example, thanks to the fences, the herbaceous layer is preserved throughout the season and finally, when it is at its maximum, we allow the local population to come and harvest to make fodder. Some use it for their own livestock; others sell it, which brings them a large profit.
The project is now fifteen years old. What is your assessment?
UK: It works very well in Senegal. We convinced the residents of the benefits of this approach and, since they were more on our side, things went well. On the other hand, there are some countries, such as Algeria, where experiments with green barriers have not worked because the population is against them. Geopolitical reasons may also compromise the project. Although all leaders want it to work, they cannot control everything.
What are the challenges for the next decade?
GA: Convince decision makers that research is essential to progress. We try daily to gather the managers of this fortress with researchers because, in order to make a decision, you need to know what the results are. We also believe that with this synergy we can convince governments to put more resources into this project and allow our research students and doctoral students to be trained in better conditions in concrete aspects. For example, for some time there was an insect that invaded one of the tree species. This insect, we were able to describe it recently thanks to research. This is a previously unlisted insect. So the research allowed an amazing development!
Do you feel like scientists in action?
UK: Action and terrain! We are not alone in our banks. We also go into the field to see what is happening with the populations. People who have knowledge to pass on about their environment.
If you had to describe this Great Green Wall project in one word…
UK: Very nice!
GA: I would say “reckless” and “conscious”.
Mr. H.M. : An “example” project! We conducted interdisciplinary research and action in contact with local populations, and it was a success. We need to announce it!
Listen too “The Knowledge Factory” is anchored in the African continent for its second season
“The Knowledge Factory” is a podcast written and hosted by Joséfa Lopez for The world. Directed by: Eyeshot. Graphic identity: Melina Zerbib. Partnership: Sonia Jouneau, Victoire Bounine. Partner: Espace Mendès-France in Poitiers.