Sltldr: “They’re just throwing away money, planting trees in the desert for them to die.”
The Great Green Wall is a top down, big government intervention that has little to no local buy-in and isn’t sustainable without continued big government funding.
Not surprisingly, the funding has mostly dried up, and so has the land.
The other issue is that not all climates are suitable for growing trees (at least with current methods and technology). Yes, human efforts can shift things a bit more in the forest direction in marginal cases but if there is no rain there will be no trees in the long term. And, unfortunately, due to carbon emissions, most of the earth is getting less suitable for trees, not more.
Some of this greening the desert stuff relies on optimism that flies in the face of basic ecology.
I mean, it’s true that not all climates are suitable for growing trees, but the Sahel area’s climate is historically suitable for growing trees, and according to again some videos I recently watched, there are actually still trees in those areas, but they look like bushes because they’ve been cut down or pruned poorly. A lot of them can be repaired just through careful pruning.
In some areas I’m sure this is true. But remember that we’re are no longer living in the historical climate. Marginally suitable for trees in the past may mean no longer suitable today. And even more so with another few decades of warming.
Smaller projects would be better to start with so we can establish what works and where. That’s why these mega-projects usually fail.
But by the same token, what is unsuitable for trees today doesn’t have to be unsuitable a decade from now. Plant growth affects the climate. Retaining moisture, stabilizing day-night temperatures, retaining topsoil, changing surface albedo, triggering cloud formation, etc.
Ideally a mega-project is thousands of small projects being attempted at once in a way that is useful even if only a fraction of them work. Those 10% of places that worked could be used as a jumping off point for further efforts in the region, and in all cases people learned valuable agriculture skills they can take with them for the rest of their lives.