Support species: fertilising, engineering trees

Support species: fertilising, engineering trees

Sometimes called support species. In French, you’ll come across the acronym AFI: Architecturales, Fertilisantes, Ingénieures — architectural, fertilising, engineering.

Without the help of support species, a food forest will develop far more slowly.

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You start with a large number of support species and few productive ones. The goal is to fully reverse that ratio over time, until support species make up only a small share of the food forest. → Support species don’t just save space, they save time.

The great difference between a natural system and one designed and managed by humans is that in nature, only a tiny fraction of total yield is directly available to us, since we are only a tiny part of all natural species — whereas in a human-managed system, almost every species is selected to provide some form of direct or indirect yield for us. We call support species the plants whose main function is to support the growth of our main productive species, by playing a key role in regulating incoming energy from the sun, wind and water, by hydrating the soil and stabilising the water cycle, by harvesting nutrients from the air (i.e. nitrogen fixation) and from different soil depths, by creating new niches to host a diversity of living organisms both above and below ground, and generally by putting the ecosystem back into function.

Starting from a bare field or meadow, planting pioneer trees — often support species — quickly builds a canopy, within a few years. This step avoids the need for inputs to rebuild living soil: pioneer trees have a positive effect on the soil through rooting, biomass creation and leaf litter decomposition. Fruit trees and lower layers are then introduced according to their light needs.

Pruning nitrogen-fixing pioneer trees enriches the soil with both carbon and nitrogen. Prune in autumn, when rainfall overtakes evaporation, to bring the light and space fruit species need to grow.

Some support species are then deliberately sacrificed, returning their wood to the soil — which opens up production opportunities for the food forest’s productive species.

Some uses of support species in a food forest

• A dense-canopy support species to shade a fruit tree or shrub that needs protection from the sun in its early years
• A few marcescent-leaved support species to shield a fruit shrub from cold winds
• A fast-growing support species to give a twining vine something to climb (choose the species carefully — this one is staying)
• Native, pioneer support trees planted in large numbers (1 per square metre) to restore life below ground and enrich the soil with their autumn leaf fall

Some support species for our climate

Latin name	Common name
Acer campestre	Field maple
Alnus cordata	Italian alder
Betula pendula	Silver birch
Carpinus betulus	Common hornbeam
Corylus avellana	Hazel
Frangula alnus	Alder buckthorn
Fraxinus ornus	Manna ash
Robinia pseudoacacia	Black locust
Rosa canina	Dog rose
Sorbus aucuparia	Rowan
Tilia cordata	Small-leaved lime
Ulmus minor	Field elm
Viburnum opulus	Guelder rose

Support species listed in our plant database

Article published by Semisto on 8 February 2025

Co-authors

Michael Hulet