Arbor Day: The Importance Of Tree Roots

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Arbor Day: The Importance Of Tree Roots

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The roots of a tree extend far from the trunk and are mostly found in the upper 6 to 12 inches of soil.

By Will Summers,

Master Gardener

Now is the time to plant trees. Arbor Day falls on Friday, April 22, which is also EARTH DAY this year. Homeowners and gardeners overlook the portion of the plant we call “roots.” In the case of tree roots, like many things, we overlook what we cannot see. Fruits, flowers, stems and leaves express themselves boldly each year as we begin our spring planting. This article emphasizes the importance and protection of tree roots. This information also applies to any shrubs and even perennial and annual flowers, vegetables or plants of all kinds.

Builders and homeowners previously thought that any land-altering activity near trees must be minimized only under the tree leaf canopy or “drip-zone.” The drip-zone is that space under the canopy of the tree limbs or where water drips through the leaves. Recent research, however, shows this not to be accurate. Studies now indicate that damaging impacts occur out to two to three times the drip-zone diameter. In fact, covering as little as 1/3 of the drip-zone of a mature white oak with as little as one inch of clay soil or 4 inches of sand will lead to mortality.

Roots are the lungs and digestive system of the tree and are easily disturbed. Roots not only continuously take in water and nutrients but are important for storage and synthesis of enzymes used throughout the tree. Roots maintain a delicate balance of moisture and gasses within the soil. Ninety percent of all roots occur in the top foot of soil. Contrary to popular opinion, tree roots do not mimic the shape of the tree underground. A tap root is a single primary root much like a carrot. Few trees maintain a tap root except during their earliest years. Most trees do not rely on a primary taproot for anything but anchoring.

Most, if not all, absorption comes from fine, actively-growing, hair-like projections from root tips or “root hairs.” Root hairs live in a close harmony with soil conditions such as aeration, temperature, moisture and pH (acidity/alkalinity).

So, what kind of impacts damage trees through their roots? The answer is: If anything occurs within the trees’ root-zone that affects the delicate balance of moisture and oxygen, then the tree is unable to absorb sufficient water and nutrients to survive. Tree roots have bacteria and fungi living on their roots and sometimes within the roots that transfer nutrients into the plant cells. You damage the health of your tree by damaging this root fungus or mycorrhizae. Studies indicate that the surface area of tree roots is two to four times the amount of surface area of the tree leaves.

Soil compaction removes air spaces, crushes roots and makes soil impenetrable. Excavation severs roots and causes soil to dry. Filling buries roots, changes surface temperature and ultimately changes the amount of moisture in the soil. All these impact the natural soil organisms the tree depends on and ultimately impacts your tree.

Changes to drainage, either by increasing water runoff or by flooding, always requires tree roots to make an adjustment to new soil moisture levels. Mature trees cannot adjust their roots, even over a matter of years, in time to survive. Trees store sufficient nutrients to live the first few years, then will gradually succumb or die of weakness to fight off disease.

A tree’s above ground mass (weight and volume) is five or six times the mass of its roots. However, if you take away the tree trunk, the leaves and branches just about equal the mass of its tree roots.

This Arbor Day, please remember if you care for your tree, you must first start by caring for its roots. For more information regarding tree care, please contact your local Master Gardener, the University of Illinois Extension office or your local public library.

The Washington County Master Gardeners invite you to the annual Plant Swap held in conjunction with the Nashville Public Library Spring Book Sale. The plant swap is held in the Nashville City parking lot on Saturday, April 23, from 8:00 to 12:00. Please bring a plant to share and take a new plant home.