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There are seven layers identified in permaculture layers and forest gardening: They are:
- canopy
- secondary trees
- shrubs
- herbaceous layer
- ground cover plants
- root crops and
- climbers.
In a mature ecosystem like that existing in an ancient woodland - there are a huge number of relationships between the component parts of the woddland, for example - trees, understory, ground cover, soil, fungi, insects and other animals.
The plants grow at different heights and this allows for a diverse community of life to grow in a relatively small space. Plants also come into leaf and fruit at varying times of the year. For example, in the UK, wild garlic comes into leaf on the woodland floor during the time before the uppermost canopy re-appears with the spring.
A woodland suffers little soil erosion as there are always roots in the soil. It also offers a habitat to a wide variety of animal life which inturn the plants rely on for both pollination and for seed distribution. The productivity of a forest like this in terms of how much new growth it produces exceeds even the most productive commercial wheat field. It is particularly in this observation of how more productive a woodland may be with far less input of manmade additions like fertilizers that the potential productivity of a layers / stacking design is modelled.
The many connections found in a woodland contribute together to an abundance of opportunities for amplifier feedbacks to evolve that maximise the energy flow through the system. . | 
