Why does this topic matter?
Roots and shoots are linked through a kind of circulatory system: what hurts the one, hurts the other.
Roots supply water and nutrients to the shoots, and get back sugar and other compounds they need to live. Roots also store food, synthesize hormones, and provide support.
Most roots lie in the top 6-18" of the soil, and usually extend far out from the trunk.
Damage to the root system can often be detected from discoloration, reduced size, or death of part or all of the tree's crown.
When does damage happen?
When something cuts the roots, or stops them from growing or breathing, it causes damage and threatens the life of the tree.
Common urban activities that often damage roots include:
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building construction |
road widening |
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utilities repair |
sidewalk replacement |
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lawn parking |
patio or paving installation |
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grade change |
stockpiling on the ground |
How do these acts hurt the tree?
Loss of support. When the big buttress roots are cut close to the tree, the tree has no support on that side and is prone to windfall.
Loss of water. Cutting the roots that supply water makes the tree vulnerable to drought, and also to pest problems that often attack water-stressed trees.
Loss of nutrients. Feeder roots must grow to take up many nutrients, and when the soil is compacted by traffic or other loads, roots are unable to penetrate it.
Loss of food. Roots, like people, must be able to breathe to use the food they get from the leaves. When roots are smothered, they die from starvation.
How can the roots be protected?
Fence off the ground underneath the tree's crown before construction begins. If traffic must go through that area, first put down 12" of gravel or coarse mulch.
Work with your utility company to tunnel under tree roots, when appropriate.
When replacing sidewalks, lay them around (or up and over) the roots of older trees.
Don't raise the soil grade over roots more than a few inches without special precautions to make sure they can get the oxygen they need.
Set paving blocks in sand, and don't mortar them together.
Mulch wide and 2-6" deep, especially younger trees trying to establish their roots.
Where can I get more information?
Alex Shigo, "Troubles in the Rhizosphere," Tree Care Industry, October 1996, 6-18. If you have trouble locating this or other materials on the topic, call your local office of the DEC or Cooperative Extension--or us at the Community Forestry Education Project, 716-461-1000.