Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
5/17/02
Contacts:
Chris Feeley, Forestry, (515) 294-6739, cfeeley@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning May 17, 2002
Preventing Construction Damage to Trees
Chris Feeley
Forestry Extension Specialist
Iowa State University
Spring has sprung! The flowering ornamental trees are putting on a display this year that is rarely matched, and the larger shade trees have flowered and are now developing their leaves. Construction is another springtime event in Iowa. Just about anywhere you look there is a new house, a new addition to an existing building, a new sidewalk or new roadway being built. I receive numerous phone calls this time of year from people asking how they can prevent construction damage to their trees. Here are some of the basic steps I use to determine which trees to save and how to protect them from construction damage.
Valuable trees are often cut down, killed or severely damaged during construction work. To save their trees, people spend a great deal of time and money only to have the tree sicken and die shortly after the construction. When faced with these problems, many people choose to remove existing trees and replant new trees when construction is finished. In spite of this, there are a few simple inexpensive steps that could be used to keep trees alive and healthy.
It is usually cheaper and easier to save an existing tree than to cut it down and replant a new tree. However, you can waste a lot of time and money trying to save the wrong tree. As a general rule, the roots out to the drip line of the tree must be protected. The drip line is the area where the branch tips end. This area is critical and must be protected from cutting, soil compaction and back filling. The tree should be removed if you cannot protect the drip line.
To decide which trees to save, identify trees that are damaged, decaying or have poor form. These trees are considered a hazard and will not be worth protecting. Next, look at the building/construction plans and determine where the structure and utility lines will be located. Use stakes and twine to accurately mark out the proposed location of buildings, roads, parking, sidewalks and utility lines. Stand back and look at the site. Decide which trees are worth saving or could be saved by making sure that construction will not interfere with the drip line. Quite often a small shift in where sidewalks, utility lines, parking or even where the building structure is located can make the difference between saving or removing a tree.
Measures should be taken to help protect the roots of the trees being saved. Most tree roots are found within the first two feet of soil and are very sensitive to compaction, so construction activities must be kept outside of the drip line. Adding a 2 to 4 inch layer of wood mulch will help preserve the soil moisture, reduce the chances of compaction and kill the competing grasses. In addition, fence in the area around the drip line and declare this area off limits for all construction activities.
Grade changes around the tree almost always guarantees a slow death for the tree. Removing the soil around the tree changes the soil moisture level. If the cut is relatively shallow, less than one foot, and the cut is made outside the drip line, the tree usually is not harmed. Removing the soil next to the trunk typically will kill the tree. Adding extra soil around the tree will smother the fine feeder roots that are located within the top one to two feet of soil. If these delicate roots die, the tree is doomed. Death from grade changes takes 3 to 5 years.
Finally, there are trees that are more susceptible or resistant to construction damage. Trees that are fairly tolerant of root damage are generally found native in the floodplains where they have adapted to constant soil changes. Examples of trees that are tolerant to root damage include silver maple, basswood, cottonwood and river birch. Trees that are moderately sensitive to root damage include sugar maple, red maple, ash, walnut, sycamore and hackberry. Trees that are very sensitive to root damage include some of the most desirable shade and ornamental trees. Sensitive species include oaks, hickories, honey locust, Kentucky coffee tree, white birch, redbud and all conifers. Great care must be given to species that are sensitive to root damage. However, if the entire root system is protected these trees should survive.
Taking these relatively simple and inexpensive steps will not guarantee that the tree will survive. However, implementing these steps will greatly increase the chances of the tree surviving. If possible, have a professional forester, arborist, horticulturist, nursery person or other tree expert help determine which species can be saved and the best way to protect them.
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