It's essentially leveraging & managing the natural succession of soil to forest. It uses support species to produce bio mass in situ, provide shade/shelter for short, medium & long term crops.

Systems are reset lightly or heavily depending on the primary crops you're focusing on & what you're wanting. This provides bio mass above ground but also collectively stimulates all plants in the system via the roots.

https://www.youtube.com/watch?v=gSPNRu4ZPvE