Cranbrook Garden (Barbara Eckstein)

The Importance of Trees in the Garden

In permaculture, forest gardening is high on our list of priorities. While the production value of certain trees, specifically fruit and nut species, is an obvious positive, there are many more reasons trees should be featured often and prominently in our designs. When considering them carefully, we can find a bounty of benefits to enjoy. Trees play a vital role in eco-systems, in the planet’s atmosphere, in our water systems, and in weather patterns. Even in suburban gardens, trees can perform many vital and useful roles, reaching beyond just food production and into establishing stable micro-climates and reducing energy inputs.

Production Value

Apple Trees (liz west)
Apple Trees (liz west)

Obviously, fruit and nut trees have enormous production value in the form of food. Even a dwarf apple tree, when mature, will likely supply several bushels (a couple hundred pounds) of apples, or there can be twenty-five pounds of hazelnuts per mature tree. In other words, with just a few food-producing trees, we gain a tremendous amount of food. However, trees aren’t only limited to fruit and nuts. Some trees—moringa, linden, mulberry—have highly nutritious, edible leaves, while others produce pods of protein-rich beans and peas. Additionally, we shouldn’t forget that many trees can be coppiced for firewood or eventually harvested for timber.

Permaculture Student

Animal Habitat

A permaculture garden celebrates the inclusion of animals, recognizing that they are necessary to create an eco-system, and trees are the habitat for many of the most important animals to a garden. Insects and birds, for one, are highly reliant on trees, namely the crown, where they make homes and perch to hunt. Many insects and, as a result, birds also flock to flowering trees for pollen or, in the birds’ case, pollinators. But, the habitat doesn’t stop there. Trees also drop an immense amount of organic matter, which provides fodder and habitat for many beneficial ground dwelling insects and arachnids, as well as worms. These, in turn, attract frogs and lizards and snakes, and the garden starts to become very vibrant with life.

Soil Creation

Lively Mulch (Support PDX)
Lively Mulch (Support PDX)

One tree drops a lot of organic matter, many times its weight over a lifetime. This organic matter then decomposes on the forest floor (or earth beneath the tree), adding nutrients to the soil. It also feeds the vast array of fauna, bacteria, and fungi that will inevitably set up shop near the tree, and these processes, too, create rich humus, via the breakdown the organic matter, the aeration that occurs because of these elements establishing themselves, and the addition of manure from the many animals. And, let us not forget those trees that fix nitrogen into the soil, or the ones that we can coppiced to create heaps of mulch material.

Erosion Protection

While trees are creating soil, they are also protecting it from erosion, and this is largely a result of all that organic matter being dropped. While hard rains on bare, unprotected soil can steal away tons of topsoil per hectare, the crown of the tree absorbs the initial onslaught of rain and, once saturated, disperses the drops that follow. When the rain does reach the ground, the soil is covered over with naturally occurring mulch dropped from the tree. This same mulch also helps to prevent erosion caused by gusts of wind that might blow through at drier times. Of course, the tree’s roots, ninety-plus percent of which are in the first two feet of soil, also help to keep the earth intact.

Water Cycles

A Mountain Stream (Vlastimil Koutecky)
A Mountain Stream (Vlastimil Koutecky)

Trees function as major factors in water cycles. The organic matter that they drop, as well as the bacteria and fungi that feed on it, all act as sponges, collecting and holding moisture rather than allowing it to drain. All of this retained water slowly percolates through the soil, being absorbed by trees roots or eventually making it to streams. Through transpiration, the tree gets nutrients then releases moisture back into the atmosphere, either via evaporation in the daytime or condensation at night. Condensation, in some climates, can provide more precipitation than rain. However, we should also note that trees cause rain, either via lifting cool wind up so that it heats and drops the rain or via cloud-forming bacteria that the wind collects off of leaves. Then, of course, trees also help block the sun from drying out the soil.

Wind Effects

Wind has a tremendous effect on trees, and trees also can affect how wind behaves. We can use established trees to judge the wind direction and intensity in an area by simply observing whether or not trees are flag-shaped and how severely so. Trees, in turn, change the way wind moves. Forests will lift more than half of the wind over them, creating conditions that cause rainfall (especially in coastal settings) on the downwind side, and the wind that does enter the forest will slow, dropping whatever debris it carries in the first 100 meters and disappearing altogether by one kilometer. Wind breaks and wind tunnels created by trees can be design features to regulate where wind moves, either creating shelters for cultivation and warmth or avenues for a constant, cool breeze.

Energy Efficiency

Passive Solar Energy (Frei Otto)
Passive Solar Energy (Frei Otto)

Because trees control water cycles and wind effects, as well as air temperature, they potentially can make homes much more energy-efficient. Obviously, if rainwater is being retained rather than drained, and more precipitation occurs because of trees, our plants will require a lot less in the way of irrigation. If the wind is either blocked by trees to keep a house warmer, or funneled in a specific direction to provide a cooling effect, it means less energy is required to artificially create these comforts. In fact, trees actually adjust the temperature in the air. During the day, water will evaporate from leaves, cooling the space beneath them, and at night, the water will condensate from leaves, warming the air around them, effectively moderating the temperature swings. Then, there is always shade trees to cool or sun traps to warm.

Clean Resources

In the meantime, trees are also doing what they do naturally. They take in carbon dioxide from the atmosphere and provide us with oxygen, cleaning the air so that we can breathe. They also help to clean the water, either by filtering out the nutrients, transpiring it back into the atmosphere, or causing conditions for the water to percolate through the earth instead of carrying away topsoil. When moisture moves down through the earth, as opposed to over it, the water gets filtered and comes out clean and clear, as we see it in mountain streams. Most urban and suburban areas are designed to drain water away as quickly as possible, so this could be hugely important. Additionally, hedges could be used to block pollution from entering a space.

Tire Swing (Rich Bowen)
Tire Swing (Rich Bowen)

Without a doubt, there are many more reasons to plant trees, such as tire swings, climbing, natural beauty, privacy, and fodder for domesticated animals. We can use them for living barriers, saving the bees, and hanging wind chimes. The point is that, whether there is only the space for a couple dwarfed fruiting species or a full-on food forest, trees more than earn their inclusion into landscape designs. Without them, our planet would deteriorate—and, due to deforestation, progressively is doing so—fast. But, they are not just vital to the planet; they are also very important in the garden.

Feature Header: Cranbrook Gardens (Barbara Eckstein)

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