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DON'T LET CONSTRUCTION DAMAGE DO IN YOUR PRECIOUS TREES
About the quickest way to kill a tree, short of cutting it down, is to build something next to it.
I get a lot of calls from folks asking what might be wrong with their tree because it's dropping leaves, or half of it appears to be dying. A few perfunctory questions generally reveal that, yes, they did dig a foundation 4 feet away last year, or, yes, they cut some roots off to put in a swimming pool.
I've driven through a number of housing developments, carved out of wooded areas, two or three years after completion; it's depressing to see mature oaks or maples wilting and dropping their leaves. Too often, the root systems of these trees were damaged during construction.
Construction damage can take a variety of forms: Severed roots from digging basements, footings, utility trenches or sewage systems; root compaction by heavy equipment; torn bark; and trunk or branch injuries; and poisoning from toxic spills.
Most large trees near proposed construction sites are worth saving. Some tree species are more sensitive to construction damage than others. Among the most sensitive to root severance are white oaks, northern pin oaks and black walnut. Trees that are sensitive to root compaction include pine, birch, basswood, maple, red oak and white oak. Prior to the arrival of construction equipment, there are some common-sense precautions that can maximize your chances of preserving your trees' overall good health.
First of all, consider that up to 95% of a tree's root system can be in the top 3 feet of soil, and more than half of a tree's roots are in the top 1 foot of soil. Professional arborists define the part of the root zone in which construction damage should be avoided as the "Protected Root Zone" (PRZ).
Historically, a common rule of thumb has been to avoid disturbing roots inside of the "dripline" - the area directly below the branches of the tree. However, since roots can extend horizontally up to two or more times the height of the tree, a safer guideline is to protect an area equivalent to 18 inches for each 1 inch of trunk diameter (e.g., for a 2-foot diameter tree, protect the area within 36 feet of the trunk).
I don't think it's a worthy goal to protect every tree around a building site. Cottonwoods, box elders, silver maples, spruce, elm and willow probably aren't worth saving, for a variety of reasons. It's better to remove these trees before construction and plant more desirable trees once construction is complete.
The best way to protect trees during construction is to agree with the builder and architect ahead of time on what trees are "off limits," and then install bright orange polypropylene fencing around the PRZ. Make sure your contractor and all subcontractors understand that nothing inside the fence is to be raked, dug, cut, driven on or dumped on.
My house near Chaska was built by Dave Durst in 1993 amidst mature bur oaks and basswoods. All the trees are still healthy today because Dave understood their value and instructed each subcontractor to follow the above rules.
Even if you want to save a tree closer than the PRZ - say 10-15 feet from the building site - there are some tricks you can use to increase the chances of a tree's survival; for details, drop me a note and we can discuss it further.
It's not always easy to save trees during construction but your efforts are worth the trouble. Healthy, well-placed trees can increase property values by up to 25%.
If you are facing a construction project, the best first-step is to consult with urban forester or arborist with experience in protecting trees from construction damage. Check the yellow pages under "Tree Service." Good luck!
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PUTTING DOWN ROOTS:
A Delightful Blend of
Gardening Wisdom, Wit
and Whimsy
$10 + $2 for shipping
by Cliff Johnson |
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