A food forest is a concept in permaculture that utilizes mimicry of natural forest systems to create sustainable and self replicating food production systems composed mostly of perennials. A properly designed system will included all 7 layers of natural forest systems and require minimal maintenance for high levels of productivity. These systems are often established with swales or via the technique of Hugelkultur though neither are required for a system to be considered a food forest.
Seven Forest Layers
Robert Hart pioneered a system based on the observation that the natural forest can be divided into distinct levels. He used intercropping to develop an existing small orchard of apples and pears into an edible polyculture landscape consisting of the following layers:
- ‘Canopy layer’ consisting of the original mature fruit trees.
- ‘Low-tree layer’ of smaller nut and fruit trees on dwarfing root stocks.
- ‘Shrub layer’ of fruit bushes such as currants and berries.
- ‘Herbaceous layer’ of perennial vegetables and herbs.
- ‘Ground cover layer’ of edible plants that spread horizontally.
- ‘Rhizosphere’ or ‘underground’ dimension of plants grown for their roots and tubers.
- ‘Vertical layer’ of vines and climbers.
A key component of the seven-layer system was the plants he selected. Most of the traditional vegetable crops grown today, such as carrots, are sun loving plants not well selected for the more shady forest garden system. Hart favoured shade tolerant perennial vegetables.
In October of 1990 Bill Mollison, who coined the term permaculture, visited Robert Hart at his forest garden in Wenlock Edge. Since that time Hart's seven-layer system has since been adopted as a common permaculture design element.
In a food forest system support species are plantings that exist primarily for the benefit of other plantings in the system rather than for direct use as food or fuel. A primary example of this is the planting of legume species of trees in a food forest system. Such trees form a symbiotic relationship with soil bacteria and fix atmospheric nitrogen into the soil. Periodically during the establishment of a food forest these species are chopped and dropped. When they are cut back they self prune their root systems and much of the nitrogen they have fixed becomes available to other species. This is one way to eliminate the need for nitrogen fertilizer.
When the cuttings of these trees are dropped they are placed as mulch around long term productive species. This mulch forms an additional nutrient cycle and further enriches soil along with reducing evaporation. Over time many support species are eventually culled out and the primary productive species take over. In general only a very small percentage of support species will exist in 5-10 years after a system is established.
Permaculturists differ in opinion about the number of species required for system establishment and maintenance. Some such as Geoff Lawton specify an initial ratio of 9 support species to every 1 long term productive tree. Others such as Mark Shepard seem to feel little is gained by planting support species at all. This wide variance in opinion is largely based on geography and local soil conditions.
If one is in a tropical system with fragile and damaged soils the need for support species will likely be very high. Where as someone in a cool temperate climate with deep and rich soils already established and natural annual leaf drop the need may be much lower or non existent.
In the end most permaculture educators see support species as valuable but base ratios on the situation on the ground and utilize what ever works best for an individual system.