Why are mixed crops cultivated in high latitude coastal environments?

Question

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?

Answer 1

It is called Companion planting, and it is actually fairly common with hand tended fields. It does not work well with mechanized agriculture which is why you don't see it much in large scale farming. It is however, fairly common in gardens and non-industrial farming because they do work well. It has a variety of benefits depending on what exactly you are planting.

The benefits here are fourfold at least. First is cramming many plants of differing heights into the same place. You also get the benefit that the large tree species provide a place for the ginger vine to grow. Some of these plants are nitrogen fixing so they help fertilize the soil, and may even share nitrogen directly via rhizome transport, basically crop rotation without the rotation. Finally ginger prefers shade to full sun.

There may be other benefits in this case I am just not seeing, like pest control.