Just because the forest has more mass does not mean it produces more food. Trees produce tons of mass in an evolutionary war to be taller than all the other trees and get more sunlight. None of it is edible though.

All of them are in a highly competitive war for resources. Plants produced poisons to kill other plants. They try to spread their seeds faster. They try to grow taller and faster and steal sunlight. They grow bigger roots to steal water.

No plant wants to be eaten, and so many produce poisons and thorns other deterrents. Few of them keep all their calories in one place, and require highly specialized digestive systems which humans don't have.

The exception is fruit plants of course, but they only produce the minimal amount of food necessary. The fruit you buy in a store has been extensively bred by humans to be so large - and this domestication has a massive energy cost that makes them uncompetitive in the wild.

Anyway the point is that the wild is not optimized for humans at all. It's an incredibly inefficient way to produce food. The plants are spending most of their resources fighting each other, and insects, and everything else. The winner of this game is whatever plants reproduce the most, not the ones humans want. Permaculture is really cool, but you are never going to get anywhere near as many calories per unit of land.

You post is great until the last sentence:

Permaculture is really cool, but you are never going to get anywhere near as many calories per unit of land.

Permaculture means living such that we don't go extinct. Having a great portion of our workforce return to bucolic agrarian pursuits is one way to get there! As they say: it beats flipping burgers.

The point of a food forest is that it has been carefully cultivated to maximize your human edibles, without needing energy expensive, oil based, or otherwise negatively impactful external inputs. When you subtract the non renewable energy expenditure, you certainly will get as many calories per unit of land!

If you are optimizing towards energy use, we could theoretically make robots or tractors that are solar powered.

But this isn't an issue at all. Farm equipment does not consume that much fuel, and fuel isn't that expensive.

The energy costs of fertilizer and pesticides are the problem not the cost of robots/tractors.

All fossil fuels are going to be gone within 5k years. Humans are several times that old and presumably humans will want to survive that. Sure, we can kick the can on this one, but it is a long term problem.

In 5-20 years we will be able to grow food 30x cheaper in highly efficient bacteria and algae tanks: https://www.reddit.com/r/Futurology/comments/31zo1r/a_future...

Who knows what we will be able to do in 5,000 years. I wouldn't worry about it.

Any agricultural system that won't support near total automation of the harvesting of staples will not be sustainable for a planet with over 7 billion people. A food forest sounds great, but there's no way to drive a combine over it and feed a hundred thousand people with the labor of one.

(an unmanaged forest generates many times more biomass per hectare than a farm field)

Biomass is not the same thing as food. Are food forests actually capable of growing more calories (or fewer calories with enough compensating micronutrients) per unit area over an extended time compared to industrialized fields?

Ah but it isn't true. What is true is that industrial agriculture is the product of pecuniary exploit, not economy of scale, and definitely not the quest for the greater good.