How would the plan to plant a wall of trees in Africa stop the spread of the Sahara?



I saw on a Real Life Lore Video that there is a plan to plant a wall of trees across Africa along the southern border of the Sahara Desert. The hope is these trees will stop the spread of the desert into the semi-arid lands bellow. Why wouldn’t the desert just overtake the trees anyways?

Link to the original video:

In: Earth Science

Deserts dont simply expand just because its hot and dry. One main reason is the loss of soil – without vegetation, soil and nutrients get blown away, and the ground looses its ability to hold water.

Trees protect the ground from erosion, provide plant matter that decays into new soil, and can protect the vegetation further inland from the desert.

Trees have a stabilizing effect on the ecosystem. They block wind, reducing the spread of sand. They provide shade, cooling the area. They provide a home/shelter for other members of the ecosystem, which can keep the soil from turning into sand

The conversion of land into a desert is a process that depends on more than just lack of rain.

Trees hold topsoil, which can absorb and retain moisture far better than bare rock or sand. Once the trees are gone, the topsoil soon goes with them, partly because it doesn’t have roots holding it in place and partly because wind can blow more freely. Once the topsoil is gone, nothing can grow there, so there’s no way to replace it.