That did not take long at all. Sprouting tree seeds in a holder is strqaight forward and mass producible. Taking those out by drone and then injedcting them into the available soil allows rapid high volume deployment.
Follow that up with a walk over to take care of obvious problems is also quick and easy.
This has been applied to mangrove lands, likely cleared originally for shrimp farming and then abandoned. This is meant to be a pretty easy target.
What it does tell us is that established agricultural land is prime for all forms of this work. The good news is that ownership and owner maintenance is completely possible here.
Stepping out into the wild is quite another matter and that does demand things like Groasis.