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The Understory Forest Layer

The understory or lower canopy trees stand lower in height than the upper canopy trees. Often, in this layer, fruit and nut trees predominate. But other trees, such as those included for edible leaves, other yields, and nitrogen fixation, are also a part of this layer.

Below and between the taller canopy trees are the plants of the second layer in a food forest or forest garden, the smaller trees or large shrubs of the understory layer.

Understory Layer: Sub-canopy Trees or Large Shrubs

In this layer of a food forest or forest garden, you will find smaller trees, coppiced or pruned trees, and/or larger shrubs. These plants occupy the spaces around and sometimes under or partially under the primary canopy species.

Sometimes, the species within this layer include some of the same species found in the overstory or canopy layer of the system. Sometimes, in smaller food forests or forest gardens, these smaller trees or large shrubs might be the tallest plants within the ecosystem.

This layer is strongly influenced by the canopy trees in the layer above it, and has an influence, of course, on all the layers below it too within the system.

In my own forest garden, a mulberry, a Siberian pea tree, and several larger, pruned Elaeagnus shrubs make up this layer, amid the larger, mature apple, plum and cherry trees.

In different climates, there may be many more trees and larger shrubs within this layer but here, where a more open canopy is better, and light needs to be managed more carefully, it is best to make sure that some light can reach lower areas to promote healthy biodiversity.

The Functions of Lower Canopy Trees

The trees and shrubs forming a lower canopy within a food forest or forest garden system fulfil several important functions within the system as a whole. Their placement can be important in defining certain areas within the system, making vegetation denser, and perhaps offering more protection to other plants close by from sun, wind etc..

Certain trees and larger shrubs within this layer aid in maintaining fertility within the system, or adding fertility to the system – through nitrogen fixation for example.

Some of these trees and shrubs of the lower canopy may be pioneer species, outcompeted as the canopy above them closes in. Some are specialists which thrive in the shade below canopy trees, or which take advantage of the period before deciduous canopy trees gain their leaves in the spring.

By taking advantage of what light there is below the canopy, the plants in this layer can be important in making sure we maximise photosynthesis as much as we possible can within a permaculture system.

Of course, like any other trees and shrubs that we might include in any permaculture scheme, the functions of trees and shrubs in this layer of a forest garden or food forest can be many and various.

Remember, whenever we look at choosing plants for any layer of a forest garden, we need to look both at their function and role within the ecosystem as a whole, and the benefits and yields that we can derive from the plants that we choose.

As with the plants in other layers of a food forest or forest garden, trees and shrubs within this layer can fulfil multiple functions of ecosystem services, and provide multiple yields, including edible yields, medicinal yields, fuels, timber, crafting materials and so much more...

When and Where Sub-Canopy Trees Are Used

Deciding where we should and should not include sub canopy trees and large shrubs in our designs can be important. While a food forest can have up to seven layers, and that layering is important, it is a good idea to keep in mind that you will not always have as many layers as that.

How many layers you have in a food forest will very much depend on the species that you select, and, crucially, where you are working on the project.

It is also important to think carefully about access to the primary fruit or nut trees and the process of harvesting. Because it is all well and good to add smaller trees among and below others, but sometimes, this may make things too congested and make it a challenge to reach ripe fruit etc..

Some things to think about when placing sub-canopy trees and large shrubs are:

  • Layout and orientation – sunlight and shade.
  • Using them in a linear forest garden or food forest style.
  • Using them to improve microclimate conditions in a food forest or area thereof.
  • Using them to protect key canopy trees and other plants from pests (like deer, for example).

Layout and Orientation – Sunlight and Shade

When it comes to the layout of a food forest of forest garden, considering sunlight and shade should be a top priority, especially in temperate climate food forests where the light will not be as strong as in the tropics.

In temperate climate food forests or forest gardens, considering the layout of canopy and sub-canopy species is particularly important, and your goal should always be to maximise biodiversity, productivity and ecological function from those plants while also finding a balance to be able to grow many further plants in and around them.

It is often a good idea to think about placing shorter trees or large shrubs on the southern side of larger, taller tree species (in the northern hemisphere). This means that they will have the benefit of some canopy protection (and potentially other benefits from canopy trees, such as nitrogen fixation for example), without losing out on too much sunlight.

Linear Food Forests

Sometimes, rather than literally placing sub-canopy trees below smaller canopy species, we might place tree rows, or linear forest garden systems, akin to hedgerows, with taller and shorter species interspersed.

This is an interesting way to implement the idea of a food forest in a smaller space, and can also help avoid potential issues with accessibility.

Improving Microclimate with Smaller Trees & Shrubs

We might also carefully use smaller trees and shrubs to create beneficial microclimate conditions for particular parts of a food forest or forest garden – sheltering certain plants from winds, for example, either over very small areas, or over larger areas as part of a windbreak hedge or shelter belt type scheme.

Protection from Pests

Smaller trees and shrubs placed in the right configuration around a food forest or forest garden area might also play a crucial role in providing some protection against grazing herbivores, or other pests that might damage your trees or other plants.

Smaller trees and shrubs, especially those with spines or prickles, can sometimes form a barrier against certain problematic species while also potentially providing a lot more in their own right, in terms of yields for us, for livestock, and for wildlife.

Remember, these are just some of the ways in which we can consider this layer within our designs. But there are of course plenty of other layout options and ways in which they can contribute to the whole of the ecosystem.

Will You Always Have More than One Layer of Trees in a Food Forest?

In a tropical or subtropical climate, dense layered vegetation is possible, and a food forest or forest garden can have a jungle-like look and feel, with a dense tree cover and a number of different tree species forming an upper and lower canopy.

It is also certainly possible in many cases to have multiple layers of trees in temperate climate food forests or forest gardens. However, there will not always be multiple tree layers in every system and in some cases, it can be preferable to keep the canopy more open, and limit canopy in order to maximize the amount of sun available for other plants in the lower layers of the ecosystem.

Choosing Sub-Canopy Trees or Large Shrubs

When choosing plants for this layer of a food forest or forest garden, the first thing to think about is, of course, making sure that you select the right plants for the right places.

You always need to take climate, microclimate, soil and any other environmental factors into account. Remember, plant selection and all other design decisions should always be made with reference to a specific site and the conditions to be found there.

Of course, you also need to think about what is required from the plants for this layer, both in terms of their ecological niche and the functions they perform within the ecosystem as a whole, and in terms of the yields you wish to obtain from them for your own needs.

Remember, all your plant choices for all the layers of a food forest or forest garden should be made not in isolation, but with reference to the whole, and to plant selections for other layers too. Be sure to think about how these plants will interact and correspond to any taller trees above them, and to the smaller shrubs and other plants below.