It emits more carbon dioxide (CO2) that nature cannot capture, shaves forests, builds roads, overexploits land, uses chemicals, fishes more than the oceans allow… In each of its activities, human beings interact with other ecosystems . But its excesses result in the decline of biodiversity. We even talk about “sixth mass extinction”. So, to compensate for these devastating effects, initiatives are 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 on ? How does it materialize on the ground? Fifteen years after its launch, what are the results? Response elements in episode 2 of “The Knowledge Factory, Season 2”, a podcast from World produced in partnership with theMendès-France space in Poitiers.
At the microphone of journalist Joséfa Lopez, Gilles Boëtsch, anthropologist, emeritus research director at 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 at the CNRS in the ChimEco laboratory and at the functional and evolutionary ecology center in Montpellier, biodiversity and overseas mission manager for 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 fragile region located near the Sahara, the Sahel, in the grip of desertification. And that by planting trees. This project adapts to the context and ecosystems of each country in which it is developed. Senegal serves as a showcase, like Mauritania at its level. But between the climate, the herds and the armed conflicts, you really have to hold on for this Great Wall to move forward!
Martine Hossaert-McKey: With the Great Green Wall, we can speak of an open-air laboratory experience! It’s a kind of mosaic where each country takes over the project in its own way, depending on its culture, land, soil texture. We are not going to 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 was essential. It was done on two criteria. First, the desires of the local populations, whose opinion was asked. Then, in the list of species that emerged, we tested a few of them in the laboratory. Finally, we kept seven, the most adapted or the most likely to adapt to a climate as hostile as the Sahelian zone. Then we grow the plants in the nursery and when they have reached a certain size, they are planted. This allows them to be a little more autonomous vis-à-vis the water. We reforest during the winter period to take advantage of the rainy season, which begins in August in the Sahelian zone, and we make furrows in the earth to trap rainwater.
How many trees have already been planted since 2007?
UK: In Senegal, we have two million plants. But, be careful, not whole trees, we are planting small shrubs, about half of which will survive.
AG : In other less hostile areas, you can go up to 68% success rate. Provided you have a serious follow-up, eco-guards who monitor and the installation of a fence to protect the plants.
Why do you have to replant so many trees in these areas?
UK: Before, people came to this area only during the monsoon, when there was water. Then they left. Today, these populations remain permanently because there have been boreholes and they practice livestock farming 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 makes things very difficult.
AG : It is difficult to convince people to reduce livestock farming, because it is a tradition and an honor among the Fulani to have as many cattle as possible.
In addition to stopping the desert, the Great Green Wall has a socio-ecological purpose. It aims to improve the living and health conditions of populations, to fight against food insecurity, against impoverishment…
M. H.-M. : This is a very good example of a nature-based solution, because planting trees helps regenerate the forest and bring back biodiversity. The tree will also allow grasses to settle underneath, it will attract new pollinators, insects. People will be able to reuse certain plants for their consumption, for fodder…
UK: The Great Green Wall also improves the health of populations. Indeed, in some countries, 30% of the inhabitants suffer from respiratory diseases because of the dust of the desert. However, if we manage to moisten the soil a little more thanks to the trees, this will cause the dust to fall. Respiratory diseases will therefore be reduced.
How did herders react to the establishment 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 have made arrangements to allow the herds to pass. Herders now realize that they derive a number of benefits from the plots that are reforested. For example, thanks to the fences, the herbaceous layer is preserved throughout the season and at the end, when it is at its maximum, we allow local populations to come and harvest to make fodder. Some use it for their own livestock; others sell it, which brings them significant income.
The project is now fifteen years old. What is your assessment?
UK: It works relatively well in Senegal. We managed to convince the inhabitants of the benefits of this approach and, since they are more on our side, things are going well. On the other hand, there are certain countries, like in Algeria, where experiments with green barriers have not worked because the populations were opposed to them. Geopolitical reasons can also compromise the project. Even if the leaders all want it to work, they don’t control everything.
What are the challenges for the next decade?
GA: Convince decision-makers that research is essential to progress. We try daily to bring together the managers of this wall with researchers because, in order to make a decision, you have to know what the consequences will be. 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 on concrete aspects. For example, for some time we have had an insect invading one of the tree species. This insect, we have been able to describe it recently thanks to research. It is an insect that was not listed before. Research has therefore allowed a phenomenal advance!
Do you feel like action scientists?
UK: Action and terrain! We are not only on our benches. We also go to 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…
G.B.: It is awesome ” !
GA: I would say “reckless” and “conscious”.
Mr. H.-M. : An “exemplary” project! We conduct interdisciplinary research and action in contact with local populations, and it is a success. We must let it be known!
“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 : Mendès-France space in Poitiers.