How Trees Help Create Healthy Soil
Healthy ecosystems are complex interrelated webs of life, and believe it or not, there is more life underground than what we can see above ground. Fertile soil is filled with billions of microscopic organisms, which provide plants with nutrients, while also creating underground channels for water and air to flow. The more of these organisms there are in the soil, the more fertile the soil is, and the better it can hold the moisture that plants need to grow.
Trees attract and help build large populations of microorganisms by sending carbon sugars out through their roots. These tiny helpers eat the sugars and give the trees exactly the minerals they require in return. This win-win relationship constantly improves the soil quality and the health of the trees. Trees also drop nitrogen-rich leaves and needles, which decay and become more food for the life in the soil. As the microorganisms in the soil process this food, their waste becomes fertilizer, which helps the plants to grow bigger and faster.
As trees help the underground organism community expand, the soil becomes more and more porous and spongy. This helps healthy soils soak up water during rains, preventing erosion and flooding, while holding in moisture for plants to use. Over decades, centuries, and millenniums, trees have helped build the soil that we now have on the planet, and in most places where trees are cut, the soil quickly degrades.
Through photosynthesis, trees convert atmospheric carbon dioxide into carbon sugars and oxygen. When soil is alive, it’s dark brown or black in color, and this is because it is rich with carbon, which is black like charcoal. The microorganisms in the soil have processed the carbon-based foods provided by the trees and deposited the carbon in the soil as their waste. Some of this waste becomes fertilizer for plants and some of it recirculates into the air, but many of the long chain carbons that get produced can stay in the soil for years or even centuries. Many scientists believe that improving the world’s soils could remove enough carbon dioxide from the air, storing it as solid carbon, to halt and even reverse climate change.
While trees are helping build up the life in the soil, they also help hold it in place. Without spongy soil, rainwater rushes off the surface of the land rather than soaking the rain into the ground, which reduces the supply of groundwater in the water table. Without tree canopies or tree roots, heavy rain can wash fertile topsoil away into rivers, causing major problems in the rivers and decreasing the fertility and resiliency of the land. When trees are present you can see soils being held in place, even on very steep mountains and the edges of rivers. Planting trees stabilizes landscapes, building and securing the healthy soil which supports all life.
When soil is exposed to direct sun in hot climates, the microorganisms in the soil can become dormant, or dry up and die. The soil then becomes lifeless dirt. The carbon in the soil combines with oxygen in the air and once again becomes carbon dioxide gas, losing the life giving properties of the soil and contributing to climate change. Tree canopies are like a roof over the soil, keeping it cool and protecting it from the sun. The shade from trees helps the life in the soil grow steadily more active and plentiful, which makes more fertile soil that is better at holding water and growing nutrient rich crops.
Even when soil is very dry and damaged, there are some tree species that can still thrive in it. These are called pioneer species or fertilizer trees. For instance, drought resistant Moringa can grow up to 15 feet in one year, even in depleted soil, breaking up the hard dry dirt and attracting soil microorganisms which reboots the ecosystem. The tree’s nitrogen rich leaves continuously drop to the ground and become compost that begins regenerating the topsoil. Moringa, which is a non-invasive naturalized species, also has a deep taproot that brings minerals up from way down in the ground. Within just a couple of years, the soil around Moringa trees can become rich enough to also plant fruit trees and other edible and medicinal plants. In as little as 4 years, an area that was becoming desert-like can instead become a food and resource rich Forest Garden.
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