May 2007 - Volume 68, Issue 5
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In this issue
NextGEN Departments
Tree Killers in Our Yards continued...
Over time, the lawn care equipment gradually rubs or chips away the lower bark of a tree. This disrupts the tree’s vascular system, which is located just beneath the bark.
Trees need to have their leaves and branches attached to their root system so water and nutrients can go up the tree and products of photosynthesis—sugars and starches that are needed for tree growth and survival—can go down to the roots.
The path up for the water is called the xylem and is located in the wood. The path down for the sugars and starches is called the phloem and is located in the bark. The growth layer of the tree, the cambium, is located between the xylem and phloem at the divide between bark and wood.
Cambium cells divide every year, making a new row each of phloem and xylem. As every school child knows, you can count the rings—xylem rows—to tell how old a tree is. Only the new portions of xylem and phloem are used for transporting food and water.
Because these vital pipelines run through the outer part of the tree, they are easily injured by the careless use of equipment.
Young trees are more susceptible to lawn equipment damage because their bark is thinner, but even older, thick-bark trees can be killed. It is the equivalent of cutting the tree down with a chain saw, only slower.
Look for Damage
The most obvious sign of tree injury is missing bark at or near the ground line, where the string flays the tree or the lawn mower deck bumps it. Sometimes you can see one or several spots where the wood is worn bare.
About This Article
Author
HELENE MILLER has worked for the Department
for nearly 30 years. She has worked in Kansas
City as an urban forester for the past 10 years,
advising city governments, volunteer groups
and homeowners on tree-related issues. She
has also worked in Kirksville, Springfield, Rolla
and New Madrid. She can be found kayaking
and bicycling when not at work.
