Individual Climate Action ✊

I am well aware that the majority of people don't want to plant food forests or have the training to plant food forests. I'm not claiming that people will do so on a large scale.

forest-based permaculture, without big machinery and economies of scale, requires a lot more human labor to maintain

Compared to using big machines and diesel fuel to do the vast majority of the work, sure, but you could say that about almost anything.

three hours of human labor and a ton of fossil fuels and chemicals

Have you tried growing wheat without the fossil fuels and chemical inputs? Compare doing that to growing a food forest.

How many hours of labor does it take to produce nine million calories from a food forest?

Not sure, but averaged out over a human lifetime, probably less than three.

How much training does it take to reliably manage a food forest?

The cool thing is that after the first few years, a forest will mostly maintain itself. Even just a few weeks volunteering would give someone the training that they'd need to get started, and then they'd learn the rest the same way that I did: through experience.

And what countries are going to accept the decrease in standard of living that comes with relocating so many labor hours to food production and away from everything else?

I think that ending capitalism and dismantling the notion of a "country" are co-requisites to fixing the food system. Of course the "powers that be" would never adopt a tree-based agricultural system when the basis of their power is an entire society dependent on grass.