I just came across an interesting article which discusses a form of agriculture the authors call 'forest gardens': https://nationalpost.com/news/canada/ancient-indigenous-forest-gardens-still-yield-bounty-150-years-later-study
While the authors' interest seems to be the persistence of the forest gardens even when untended for a long time, mine is in the tradeoffs involved with that form of agriculture; I'm used to the idea that you grow just one crop per field (perhaps rotating, but one at a time). Yet,
In coastal forest gardens, crabapple, hazelnut, wild cherry and plum trees provide a canopy, shielding plants such as cranberry, elderberry and hawthorn, wild ginger and wild rice root.
So why did those people mix the various trees, bushes, herbs and rice that way? Presumably there was some advantage in doing it like that, but the explanation cannot explain too much; it cannot be of the form '... so that's why it's the most efficient way in general', because that would incorrectly predict such mixed gardens in the rest of the world.
The area in question seems to be around mid fifties latitude, and the article does casually use the word 'shielding', so my first thought was perhaps that far north, herbs and bushes gain more benefit from having trees around to block the freezing wind, than they lose from having some of the sunlight blocked. Except it's also on the coast, and apparently does not get much snow in winter. It presumably gets ocean storms, but so do coastal regions in general, and I'm not aware of any other coastal regions having mixed forest gardens.
So what is the reason for that form of agriculture in that location?