Tree Killers in Our Yards

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Published on: May. 2, 2007

Last revision: Nov. 30, 2010

Would you let someone come in to your yard with a chain saw and cut down all your trees? Would you do it yourself? How about the trees in your city park?

Trees provide many benefits, including increased real estate values, reduced heating and cooling bills, reduced storm water flows, shady places to play and park and noise buffering. They are usually considered assets around homes and cities. Yet, many people are gradually killing their trees with their lawn care equipment.

Recently, an acquaintance of mine stopped me in the grocery store. She knew I was the urban forester for her region, and she wanted me to contact a local city government about some lawn maintenance contractors who were hitting “her” tree—one which had been planted in her honor at a nearby city park.

She knows what many people do not know: that trees can be seriously injured or killed when they are repeatedly hit with lawn mowers and string trimmers. I see this all the time in yards, city parks, commercial developments and other places that have trees and lawn.

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

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