Smaller trees are ‘nurseried’ in with the help of faster-growing canopy trees; in other words, the upper canopy helps shade and protect the sub-canopy from scorching sun, high winds, pounding hard rain and hail, etc. However, sub-canopy trees can also be made of the slower, longer-lived canopy trees that will eventually dominate the plant guild/forest. I’ve talked about how, if an area of forest was wiped clear and roped off, in a hundred years the beginnings of a hardwood forest will have begun. This is due to succession plants making the soil ready for the next. Each plant has a purpose. This phrase is an essential mantra in permaculture because it lets you understand what the plants are doing and then you can let them do it. So if you planted a fast-growing soft wood canopy tree, maybe even one that is a nitrogen-fixer, such as ice cream bean, or acacia, with a sub-canopy trees that include both something that is going to stay relatively small such as a semi-dwarf fruit tree, along with a slower growing, hardwood tree such as an oak which will eventually become the true canopy tree years down the line, then the original softwood tree would eventually be sacrificed and used as mulch and hugelkultur after the hardwood tree had gained enough height. Wow, that was a long sentence. At first that hardwood tree would be part of the sub-canopy until it grows up. Meanwhile there are other true sub-canopy trees that stay in that height zone for their life.
Remember, too, that plant guilds are relative in size. If you have a small backyard you may not have room for a tall canopy tree, especially if it is detrimental to the rest of the property. So scale the whole guild down. Canopy for you could be a dwarf fruit tree, and sub-canopy could be blueberry bushes. In a vegetable setting the canopy could be corn or Jerusalem artichokes, where you either leave the dead canes up overwinter (a great idea to help the birds), or chop and drop them to protect the soil, which mimics the heavy leaf drop from a deciduous tree. The plant guild template is the same; the dimensions change with your needs and circumstance.
So sub-canopy buffers sunlight coming in from an angle.
It receives rain from the upper canopy further slowing it down and shattering the droplets so that it doesn’t pound the earth. The lower branches also help catch more fog, allowing it to precipitate and drip down as irrigation. Leaves act as drip irrigation, gathering ambient moisture, condensing it, helping clean it, and dripping it down around the ‘drip line’ of the trees, just where the tree needs it.
With its sheltering canopy it holds humidity closer to the ground. In the previous post I talked about the importance of humidity in dry climates for keeping pollen hydrated and viable.
It further helps calm and cool winds, and buffers frost and snow damage. Sub-canopy gives a wide variety of animals the conditions for habitat: food, water, shelter and a place to breed. While the larger birds, mostly raptors, occupy the upper canopy, the mid-sized birds occupy the sub-canopy. Depending upon where you live, a whole host of other animals live here too: monkeys, big snakes, leopards, a whole host of butterflies and other insects using the leaves as food and to form chrysalis, tree squirrels, etc. Although many of these also can use canopy, it is the sub-canopy that provides better shelter, better materials for nesting, and most of the food supply. And again, the more animals, the more organic materials (poop, fur, feathers, dinner remains) will fall to fertilize the soil.
Sub-canopy gives us humans a lot of food as well, for in a backyard plant guild this can be the smaller fruit trees and bushes.
Sub-canopy also provides more vertical space for vines to grow. More vines mean more food supply that is off the ground. A famous example of companion planting is the ‘three sisters’ Native American method… what tribe and where I’m not sure of… where corn is planted with climbing beans and vining squash. The corn, as mentioned before, is the canopy, the beans use the corn as vertical space while also fixing nitrogen in the soil (we’ll discuss nitrogen fixers in another post), and the squash is a groundcover (also will be covered in another post). There is more to the three sisters than you think. Raccoons can take down a corn crop in a night; however, they don’t like to walk where they can’t see the ground, i.e. heavy vines, so the squash acts as a raccoon deterrent. To stray even further off-topic, there is also a fourth sister which isn’t talked about much, and that is a plant that will attract insects.
Back to sub-canopy, while some of it can be long term food production trees or plants, it too can also have shorter chop-and-drop trees. Chop-and-drop is a rather violent term given to the process of growing your own fertilizer. Most of these trees and plants are also nitrogen fixers. These fast-growing plants are regularly cut, and here is where the difference between pruning and chopping comes to bear, because you aren’t shaping and coddling these trees with pruning, you are quickly harvesting their soft branches and leaves to drop on the ground around your plant guild as mulch and long term fertilizer. If these trees are also nitrogen fixers, then when you severely prune them the nitrogen nodules on the roots will be released in the soil as those roots die; the tree will adjust the extent of its roots to the size of its canopy because with less canopy it cannot provide enough nutrients for that many roots, and it doesn’t need that many roots to provide food for a smaller canopy. Wow, another huge sentence. In this system you are growing your own fertilizer, which is quickly harvested maybe only a couple of times a year. Chemical-free. So, by planting sub-canopy that is long term food producing trees such as apricots or apples, along with smaller trees and shrubs that are also sub-canopy but are sacrificial to be used as fertilizer such as senna or acacia or whatever grows well in your region, you have the most active and productive part of your plant guild.
Sub-canopy, therefore, provides shelter for hardwoods, provides a lot of food for humans as well as habitat for so many animals, it provides fertilizer both because of its natural leaf drop and because of those same animals living in it, but also as materials for chopping and dropping, it buffers sun, wind and rain, holds humidity, offers vertical space for food producing vines which will then be in reach for easier harvesting, and much more that I haven’t even observed yet but maybe you already have.
The next part of the series will focus on nitrogen-fixers! Stay tuned. You can find the entire 9-part Plant Guild series here: Plant Guilds: What are they and how do they work? The first in a series. , Plant Guild #2: Canopy , Plant Guild #4: Nitrogen-Fixers, Plant Guild #5: Mining Plants, Plant Guild #6: Groundcovers, Plant Guild #7: Vines, Plant Guild #8: Insectiaries, Plant Guild #9: The Whole Picture.