I own both volumes of Edible Forest Garden, but they are lent out for most of the time; hence a question that may be answered in the book.
It is my understanding that in setting up a forest garden, the soil is of utmost importance. It must be ready to be planted. In natural forests humus is built up by pioneering species before the climax species enter the stage.
This makes the soil ready for healthy mycorrhizal relations.
This stage is often skipped or overlooked in designs I've seen. What is your advice on building the soil when the trees are already planted?