Effects of Tree Roots on Soil

Full of benefits, trees have an enviable position in any landscape, shade, controlling soil erosion, home to many birds, fruits and flowers. Of all the parts of a tree, the roots are perhaps the most unappreciated, as they are unseen.

Roots
There are two types of roots; primary roots that grow deep down vertically into the soil and secondary roots that branch out horizontally. The architecture of the root system is to absorb water and inorganic nutrients and anchor the plant to the ground.

Effects
The roots affect the soil, depending on the type of the tree and the soil. These effects have a direct impact on all the plants grown near the tree. Normally a healthy tree represents healthy soil. A big tree takes up most of the water available in the soil, leaving the other plants dry. Growing as well as mowing lawn grass is another difficulty around a large tree, especially if the roots are protruding outside. Tree roots help control soil erosion, however in some cases the roots have a negative effect on the soil by causing a phenomenon called allelopathy.

Allelopathy
Derived from two words; allelon which means of each other and pathos which means to suffer. It refers to the chemical inhibition of one species by another, by releasing a chemical affecting the development and growth of surrounding plants. In other words, plants try to get their own space, by restricting other plants from growing too close to them. Allelopathic chemicals secretion are not just restricted to the roots, they are also found in branches, leaves, flowers and fruits. The decomposed leaves and bark affect the top layer of soil, while the roots affect the surrounding soil. The chemical curtails the root growth of other plants by inhibiting their nutrient source, thus influencing their evolution and distribution.

Juglone
It is an aromatic organic allelopathic compound occurring naturally in the roots, bark and leaves of trees in the Juglandaceae family. It releases certain enzymes that inhibits the metabolic function, stunting the growth of many plants and at times even killing an allelopathy intolerant plant. The quantity of Juglone released depends on the weather and soil conditions. The black walnut is the most commonly known for its allelopathic properties. When Juglone sensitive plants come within 0.5 to 0.25 inches of the tree roots, they turn yellow, wilt and die. This in turn, also infects the soil.

Allelopathic Trees
Besides the black walnut, the following are trees with allelopathic properties:

• Sugar Maple
• American Sycamore
• Eucalyptus
• Cottonwood
• Black Cherry
• Red Oak
• English Walnut
• Juniper

Reducing the Effects of Allelopathy
It would not be sensible to just uproot large allelopathic trees, instead just a few precautions could be taken. A well drained and aerated soil determines the amount of chemical accumulation and the presence of microorganisms in the soil breaks down the toxic chemicals. Keeping the soil healthy by adding organic matter on regular basis can go a long way in keeping all the plants healthy. Plants can also be grown in containers and pots around the allelopathic tree, just make sure that they get enough sunlight. Another way of ensuring a healthy landscape, is to grow a variety of allelopathic tolerant plants. Some of them are:

• Hawthorn
• Flowering dogwood
• Tulip tree
• Hydrangeas
• Hibiscus
• Daffodils
• Day lilies
• Virginia Creeper

A tree must be enjoyed, even if some of their qualities are harmful to others. It would be easy to uproot an allelopathic tree or plant, but a good gardener should find ways to grow them all together.