Decay Can Cause Hazardous Defects in Trees

January 19, 2006

Tree failure is a major cause of residential property damage, as well as the leading cause of power outages nationwide. An ice storm can overload all the branches on a tree, a hurricane or high wind can blow down a tree if its roots are restricted, or a cracked tree can fail under its own weight.

"Homeowners worried about trees falling and damaging property should call a professional arborist in for an inspection," advises Peter Gerstenberger, senior advisor for safety, standards and compliance with the Tree Care Industry Association.

Gerstenberger notes that trees are designed to withstand storms, but all trees can fail ‚ and defective trees fail sooner than healthy trees. A sound tree becomes potentially dangerous when the treeís woody structure is weakened by one or more defects. During storms, pre-existing defects predispose trees to failure.

"To a professional arborist," notes Gerstenberger, "defects are detectable signs that a tree has an increased potential to fail." Broadly defined, there are seven categories of defect: decayed wood, cracks, root problems, weak branch unions, cankers, poor tree architecture, and dead trees, tops or branches.

Healthy, well-maintained trees growing on suitable sites will be able to minimize the extent of decay and other defects. Trees that are stressed have reduced energy reserves, and therefore, have less ability to deal with wounds and the ensuing decay.

Most urban trees survive on construction-altered soils that may be compacted, poorly drained, high in clay, sand, or gravel, very alkaline or littered with construction debris. Additionally, many urban trees are subjected to chemicals such as deicing salts, herbicides and fertilizers commonly used in landscape maintenance. Poor tree maintenance is another contributor to stress. These cumulative stresses all take a toll on tree vitality and structural integrity, increasing the risk of failure.

All defective trees cannot be detected, corrected or eliminated. Although a professional arborist can readily recognize most defects, there are root problems and some internal defects that are hidden. These trees may require in-depth assessments and specialized diagnostic tools. Homeowners should also keep in mind that defects change with time. A tree that looked fine three years ago may have severe problems today. By doing regular inspections arborists can successfully manage the risk of tree failure.

Advanced decay and cavities, results in less structural strength and reduced stability. Indicators of advanced decay are rot ten wood, fungal fruiting bodies, cavities, holes, open cracks or bulges in the wood. Decayed wood is the result of the long-term interaction between a tree and decay-causing fungi. Wood decay is an internal process with just a few external indications, such as mushrooms, conks, rot ten or punky wood, cavities, hollows, holes, inrolled cracks, and bulges in the wood.

The undecayed layer surrounding the decay column is called the shell. If the shell thickness is thin relative to the size of the tree, the shell is likely to fracture causing the tree to fail. A tree can have internal decay and an opening and still be structurally sound provided that the shell is thick enough and the opening is not too wide.

If a tree is repeatedly wounded by the presence of inrolled cracks, included bark, canker-rot fungi, or equipment (mowers, plows, and weed whips), decay occurs in every annual ring of wood. These trees should be carefully inspected by a professional arborist because they do not form a sound shell of wood. The tree is likely to fail at or near the location of the crack or wound because a large and ever-expanding column of decay is present there. Again, a professional arborist can evaluate shell thickness and opening width to help determine the treeís potential for failure.

Visual assessment by a trained arborist of the extent of decay can often be a reliable means of predicting potential risk. However, invasive techniques may be needed to quantify the thickness of the sound shell of wood in comparison to the size of the tree. Use of a probe or another tool may be needed to test several areas in order to find the location of the thinnest shell of sound wood.

In-depth assessments, using specialized diagnostic tools, may be warranted when additional information about the location and ex tent of internal decay is critical to assessing the probability of tree failure.

What can you do?
For additional information go to our web site at www.SY and read about choosing a contractor and references on the home page. With years of experience and education, I am able to assess and detect most problems with trees. However, if your problem exceeds my knowledge, we have two consulting arborist and one botanist with college degrees available for further consultation. Give us a call today for all your tree care needs.

Reprinted from Tree Care Industry Magazine.

For more information please contact your local tree care specialist. 688-5580

Click here for the pdf version of this article


Santa Ynez Valley Tree Care
P.O. Box 1147, Santa Ynez, California 93460

(805) 688-5580

[Home] [About Us] [Choosing a Contractor] [Licensing] [References] [Proper Pruning]
[Why Topping Hurts] [Mature Tree Care] [Newspaper Articles] [Magazine Articles]