Plant Guilds #2: Upper Canopy
Whether you are planting small plants in pots, ornamentals in your yard or a food forest, you need plants that will provide an upper canopy for others. If you have small plants, then you will have a short canopy. Maybe your canopy is a tomato plant. Maybe its an oak. Whatever it is, canopy has many functions.
Upper canopy provides shade so that other plants can grow. It drops leaves, bark, flowers and seeds and/or fruit to provide compost and food for all levels of animals down to soil microbes. Canopy provides protective shelter for many kinds of mammals, birds, reptiles and insects as they hide under the leaves. A mature oak is home to over 300 species. Old scarred canopy full of holes is the natural home for honeybees, and many types of bird and other animal. It is a storage unit for acorns gathered by woodpeckers. Where you have animals, you have droppings. All the poo, feathers, regurgitated pellets, fur, scales and other organic waste that falls from canopy is vitally important for the health of the soil below.
Canopy provides a perch for raptors and larger birds that help with rodent control.
Canopy helps slow the wind; the fewer trees we have the harder the winds. Canopy also filters the wind, blocking dust and other debris. Canopy helps cool and moisturize the wind. The leaves of canopy trees help buffer the rain. Rain on bare ground is as compacting as driving over the dirt with a tractor. If rain hits leaves it bounces, rolls or shatters. Rain can then hit other layers below the canopy, finally rolling through leaf mulch to percolate into the soil without compacting it.
Canopy catches moisture as well. Here in Southern California we may not receive a lot of rain, but we do have moisture during the night. Often I’ve walked through Finch Frolic Garden of a morning to feed the hens, and the garden sounded as if it had its own special rain cloud over it. That is because moisture condenses on the leaves and rolls off. The more canopy and the higher the canopy, the more water we can collect. In that same way, canopy begins to hold humidity on the property, which the rest of the guild contributes to. Pollen dries out. With longer, hotter, drier summers there is worse pollination even if the pollinators are active, because the pollen isn’t viable. Less humidity equals fewer fruits, nuts and vegetables. Therefore, the more canopy, and other parts of a guild, the moister the air and the better the harvest.
Canopy is in connection with all other plants in its community, linked via webs called mycorrhizal fungi. Through these webs the canopy sends chemical messages and nutrients to other plants. Every plant in the community benefits from the strong communications from the canopy trees.
Canopy builds soil. Canopy trees are large on top and equally large underground. Tree root growth can mirror the height and width of the above-ground part, and it can be larger. Therefore canopy trees and plants break through hard soil with their roots, opening oxygen, nutrient and moisture pathways that allow the roots of other plants passage, as well as for worms and other decomposers. As the roots die they become organic material deep in the soil – effortless hugelkultur; canopy is composting above and below the ground. Plants produce exudates through their roots – sugars, proteins and carbohydrates that attract and feed microbes. Plants change their exudates to attract and repel specific microbes, which make available different nutrients for the plant to take up. A soil sample taken in the same spot within a month’s time may be different due to the plant manipulating the microbes with exudates. Not only are these sticky substances organic materials that improve the soil, but they also help to bind loose soil together, repairing sandy soils or those of decomposed granite. The taller the canopy, the deeper and more extensive are the roots working to build break open or pull together dirt, add nutrients, feed and manage microbes, open oxygen and water channels, provide access for worms and other creatures that love to live near roots.
Canopy roots have different needs and therefore behave differently depending upon the species. Riparian plants search for water. If you have a standing water issue on your property, plant thirsty plants such as willow, fig, sycamore, elderberry or cottonwood. In nature, riparian trees help hold the rain in place, storing it in their massive trunks, blocking the current to slow flooding and erosion, spreading the water out across fields to slowly percolate into the ground, and turning the water into humidity through transpiration. The roots of thirsty plants are often invasive, so be sure they aren’t near structures, water lines, wells, septic systems or hardscape. Some canopy trees can’t survive with a lot of water, so the roots of those species won’t be destructive; they will flourish in dry and/or well-draining areas building soil and allowing water to collect underground.
In large agricultural tracts such as the Midwest and California’s Central Valley, the land is dropping dramatically as the aquifers are pumped dry. Right now in California the drop is about 2 inches a month. If the soil is sandy, it will again be able to hold rainwater, but without organic materials in the soil to keep it there the water will quickly flow away. If the soil is clay, those spaces that collapse are gone and no longer will act as aquifers… unless canopy trees are grown and allowed to age. Their root systems will again open up the ground and allow the soil to be receptive to water storage. Again, roots produce exudates, and roots swell up and die underground leaving wonderful food for beneficial fungi, microbes, worms and all those soil builders. The solution is the same for both clay and sandy soils – any soil, for that matter. Organic material needs to be established deep underground, and how best to do that than by growing trees?
In permaculture design, the largest canopy is often found in Zone 5, which is the native strip. In Zone 5 you can study what canopy provides, and use that information in the design of your garden.
How do you achieve canopy in your garden? If your canopy is something that grows slowly, then you will need to nursery it in with a fast-growing, shorter-lived tree that can be cut and used as mulch when the desired canopy tree becomes well established. Some trees need to be sacrificial to insure the success of your target trees. For instance, we have a flame tree that was part of the original plantings of the garden. It is being shaded out by other trees and plants, and all things considered it doesn’t do enough for the garden to be occupying that space (everything in your garden should have at least three purposes). However a loquat seeded itself behind the flame tree, and the flame tree helped nursery it in. We love loquats, so the flame tree may come down and become buried mulch (hugelkultur), allowing that sunlight and nutrient load to become available for the loquat which is showing signs of stress due to lack of light. With our hotter, drier, longer summers, many fruit trees need canopy and nurse trees to help filter that intense heat and scorching sunlight. Plan your garden with canopy as the mainstay of your guild.
Therefore a canopy plant isn’t in stasis. It is working above and below ground constantly repairing and improving. By planting canopy – especially canopy that is native to your area – you are installing a worker that is improving the earth, the air, the water, the diversity of wildlife and the success of your harvest.
Canopy is improving the water storage of the soil and increasing potential for aquifers. The more site-appropriate, native canopy we can provide in Zone 5, and the more useful a canopy tree as the center of a food guild, the better off everything is. All canopy asks for in payment is mulch to get it started.
Next week we’ll explore sub-canopy! 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 #3: Sub-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.