Predicting Tree Failure
Written by: Rick Abrahamson
Stem girdling roots (SGRs) grow in contact with tree or shrub stems. This girdling causes a
restriction on the stem compressing the xylem and phloem within the stem making it very
difficult for the tree to move water and sap from the roots to the crown and vice versa. In
addition to problems associated with translocation of water and sap in the tree SGRs create a
weakness in the stem that worsens each year.
SGRs create a depression in the stem similar to placing a rubber band on a balloon and inflating.
The rubber band restricts how the balloon can stretch causing a depressed area. The area above
and below the SGR will enlarge and may even "grow over" the constricted area, however, the
damage is still there and the tree may break even in a mild wind.
Tree decline is a term professionals use to describe why a tree is dying without really knowing
what is causing the problem. Often, trees in decline have experienced long-term drought,
repeated defoliation, SGRs, or other factors that cause a reduction in the trees normal reserves of
chemical energy. When the reserves are depleted the tree can have difficulty in leafing out in the
spring and dealing with the harsh realities of urban life in the landscape. Eventually, the tree will
have difficulties in capturing and storing (photosynthesis) additional energy reserves causing a
"decline spiral" to a certain premature death. The first symptoms observed when SGRs are
causing the decline may be leaf scorch or leaf wilting when other trees in the area are not
showing symptoms. Soon, a tree with an SGR may exhibit early fall coloration, early leaf drop
or slow leaf-out in the spring.
Research has shown that many declining and failed trees are the result of SGRs. The University
of Minnesota concluded that 80.2 percent of 220 trees in decline, SGRs were the only causal
agent. These trees had significant stem compression and had been planted 12 to 20 years earlier.
They also found that trees planted too deeply or too much mulch placed over the roots
predisposed the tree to SGRs. During a study on wind damaged trees they concluded that
boulevard trees with 6 to 10 inch diameter trunks snapped off at compression points at a depth of
4 or more inches below the ground. Often the weather is blamed on tree failure which results in
the tree being hastily removed and replaced without regard to why the tree failed. In a study to
determine which trees are most often planted too deeply it was concluded that sugar maples are
almost always planted too deep while hackberry is least likely to be too deep.
The only question that remains is "what can be done about SGRs"? First and foremost don't
plant trees too deep. Assuming that trees in containers are already planted too deeply, remove
the extra soil and find the root mass. The root mass should be one inch below the soil surface.
Don't pile mulch against the trunk. Leave an area about three inches from the trunk. If you have
trees that you suspect may have SGRs investigate. Complete a root collar examination using a
trowel and a wet-dry vacuum, remove the soil until the root mass is found. If SGRs are found
remove them. If the roots are too deep do not replace the soil. If nothing is done the problem
will only get worse. If during the root collar exam you find sever compression of the stem it
might be best and safest to remove the tree and replant.
If you have questions about this article or other horticultural topics feel free to contact me at 605-
394-2188 or e-mail to firstname.lastname@example.org.