In 2015 Living Systems Institute constructed a hugel mulch in the space of an old apple tree approximately 24' X 12'.
That hugel mulch was planted out as a forest as opposed to an orchard. In an orchard spacing is done to maximize the productivity of each tree. Then, if there is a late frost or disease outbreak the entire crop can be lost. A forest is planted to a polyculture of trees shrubs and forbs to maximize the productivity of the "guild" of plants.
If anything we planted too many plants too close together. We hope to observe how the plants interact and learn from that observation to produce highly productive forest islands for the front range of Colorado.