I have to imagine that blanketing an area with seeds dropped from a flying drone would be far more effective than a ground based robot which planted trees. Obviously the success rate of a ground based robot would be far higher, but I think we'd be better off going for quantity over quality.
If that assumption is true, then we already have the tech to do this.
I recall when HN was discussing dropping seeds from an AC-130 few years ago, someone pointed out that it would be much more cost-effective to just hire locals to do it by hand. The same will probably apply to drone-planters.
Not even "locals" - depending on location, you could bus in (or even fly in) masses of low-paid low-skill workers from somewhere else, like it happens for other agri tasks.
It was tongue-in-cheek. Because if we'd be allowed to deploy a robot to stop loggers, then we'd also be allowed to just not let the loggers log.
The problem is humans are taking over nature. Planting a couple of trees here and there is pointless if you're going to cut them down again for real estate or farm developments.
If that assumption is true, then we already have the tech to do this.