Tree Suicide and Girdling

With trees all around us, it is sometimes difficult to remember that they are living organisms, subject to some of the same problems of other living things. Trees can be murdered, and they may even commit suicide. The difference, however, is that their murder or suicide is not intentional, but often the result of carelessness or abuse.

It may seem extreme to call a condition where a tree kills itself suicide, and yet trees are able to cause their own death. This comes about by a condition know as girdling. This self-strangulation occurs when a tree root develops so that it encircles the base of the trunk, usually just below the soil surface.

Although girdling roots may occur naturally, the condition often develops when plants have been growing in pots long enough to develop a few roots that circle the containers. If these encircling roots are not cut at planting time, they sometimes can constrict the trunk as both the root and trunk enlarge, pressing against each other.

This pressure from the girdling root on the trunk cuts off food and water movement that can seriously weaken and perhaps kill the tree. Where a girdling root exists, there is often a lack of enlargement at the point where the base of the trunk enters the ground as well a poor top growth.

If a girdling root is suspected, the soil should be carefully removed from around the base of the trunk for closer inspection. If a girdling root is found, cut it away as much as possible and take care not to damage the main trunk. Then replace the soil.

Plants are not only capable of strangling themselves, but some can actually strangle other plants. Vigorous twining vines that are growing up a tree may encircle the main trunk or branches and gradually kill them. Wisteria, bittersweet and trumpet vine are capable of causing this type of damage if they are allowed to grow on trees.

While cases of plants killing other plants by strangulation are relatively rare, plant murders by people are much more common. Wires for clotheslines, hanging plant labels, or other supports do not expand as a tree grows and eventually the wire girdles it. At times, the trunk swells, covers the wires and heals back so the tree survives. The trunk is usually weakened at the point. Even heavy rope, especially rope made from nylon, can also girdle trees if left too long.

Tree girdling can also occur when a dog chain is looped around the base of a tree. As the dog moves and pulls on the leash, the chain can gradually saw through the bark of the tree, causing damage and eventual death.

In addition to conditions that girdle trees, much damage is also done to tree trunks by bruising. Perhaps the most severe damage is done to young trees that have relatively thin, soft bark, although it is also undesirable to bump mature trees.

A bump may seem light, and perhaps no visible damage is done. However, the tissue can be killed in such bruised areas. The bark then dies and becomes loose. This allows certain disease-causing fungi to invade and begin growing. If conditions are right, they may continue to grow unnoticed beneath the bark and gradually weaken or kill the tree. Dead cankers may develop as depressed, perhaps slightly darkened spots on the trunk.

What is tree decline? Decline is a term used to describe a tree that is generally deteriorating. This deterioration may be the result of many things. The symptoms often occur because the translocation system of the tree has become disrupted. The root system may be restricted or damaged. The trunk tissues may be blocked, wounded, or infected by some agent. Decline also results when a tree's food reserves are depleted.

What are the symptoms of tree decline? Symptoms are usually subtle and slow in developing. Premature fall coloration, smaller and fewer leaves, and early leaf drop are usually early symptoms. As the condition worsens, some branches may die, beginning at the top of the tree progressing downward. Leaf scorch or edge browning may occur. Leaf scorch can also result from relatively minor drought problems. Trees suffering from decline may survive indefinitely or they may die within a year or two.

What are some causes of tree decline? Decline can result from anything that restricts, damages, or impairs root or vascular systems. Late spring frosts or summer droughts also lead to decline because the food reserves have been depleted from dropping foliage. In many cases, a combination of causes may be involved. Some of the factors involved might be:

a. Root cutting -- trenches, foundations, etc.
b. Trunk wounding -- mower or farm equipment, etc.
c. Soil fill or removal from under tree canopy
d. Air pollutants
e. Natural gas leaks into soil atmosphere
f. Herbicide injury
g. Repeated droughts -- thin soils that undergo widely fluctuating water stresses
h. Excess soil moisture
i. Repeated defoliations -- perhaps due to insect damage or hail
j. Fertility imbalance
k. Girdling roots

Check the base of the tree trunk. The base of a healthy tree usually flares out as it enters the soil. This is the result of the enlargement of the lateral root system where the roots join the trunk. If the trunk has no flare but goes straight into the soil it is usually an indication of either a girdling root or excessive fill soil. With excessive fill soil the absence of the flaring trunk base is usually noticeable around the entire trunk. Often a girdling root or other obstruction will be noticeable on one side of the trunk. Digging away the soil with a trowel or spade will usually disclose the reason for the absence of the flaring trunk. Take care not to injure the trunk and roots any more than necessary in removing the soil.

How can decline be checked or controlled? In the case of a girdling root or an obstruction, careful removal of the cause will frequently allow the tree to overcome the injury. Damage from excessive fill soil is less easily corrected. In fact, by the time the decline in growth is noted it is usually to late to save the tree.

Most good, general tree care practices should contribute to controlling tree decline. Fertilize trees in late fall (October) with a winterizer (ratio of 3-1-2 fertilizer such as 15-5-10) and spring (February) with a slow-release formulation such as 19-5-9. Water deeply and thoroughly during drought. Prevent wounds as much as possible. If decline begins in a tree, thin out the top by selective pruning. Aerate the soil if needed. If a tree has been removed due to decline, do not replant the same type in the same location unless the cause has been determined and corrected.