Protect Your Trees from Construction Damage
Trees add value to the home landscape. So, it only makes sense that we would want to protect and preserve them. Not many people are aware of the ways in which construction activities damage or kill trees. No matter how insignificant the perceived impact might be, considerable harm may be done. Often the damage is inadvertent by an unknowing individual and can be minimized or avoided, but it takes pre-planning.
Most property owners and contractors have little knowledge of trees. How tree root systems grow and respond to being damaged elude them. They don’t understand a tree’s basic needs for water, oxygen, mineral elements, and how they acquire them. They aren’t aware of the role a healthy soil plays in root development and how easily it can be destroyed Roots seldom grow deeper than 36 inches in the soil. Most roots grow away from the tree horizontally and can extend well beyond the tree’s dripline. The all-important feeder roots, grow predominantly in the top 10 inches of soil. Feeder roots are the most easily damaged when any form of construction takes place.
The following activities cause damage to a tree’s root system:
Replacing a sidewalk or driveway.
Digging a foundation.
Trenching for an underground utility line.
Changing the grade by removing soil.
Adding soil fill. Just a couple of inches depending on soil type can be quite damaging.
Compacting the soil with heavy equipment.
Changing the soil chemistry.
The type of damage and degree to which damage occurs will influence symptom development. It may take up to several years for the tree to decline and become a hazard. Root Severance – Results in the trees reduced ability to absorb water, oxygen and mineral elements. When extensive damage occurs in close proximity to the tree, stability may be compromised. Skimming just a few inches of soil from the surface can cause major root damage, as can trenching within several feet of the tree. A 1 inch wide and 10-inch-deep trench can be as damaging as a trench 4 feet wide and 8 feet deep. For new utility line placement, tunneling or boring under a tree’s root system can reduce root damage by 25%.
Broken Branches – Become a hazard and deform the crown. Broken bark and damage to the tree’s trunk and limbs can disrupt water and nutrient transport, growth regulator flow and energy distribution. Any wound is an open invitation to decay.
Soil Compaction – Soil structure and composition are changed by activities that include soil compaction by heavy equipment, grade changes, soil fill, and new pavement. Soil drainage, oxygen penetration, root penetration and root health are all adversely affected.
Soil Chemistry Changes – Soil chemistry is most frequently changed when crushed limestone or gravel are applied over or near a tree’s root system. Certain tree species like Pin oak, Red maple, Birch trees and White Pine are sensitive to these changes. Misapplied fertilizer applications lead to problems that can be hard to overcome.
It is easier to avoid or minimize tree damage, than it is to correct after the damage is already done! There are several pre-construction steps that can be taken and have proven effective in that respect.
The question most often asked is “How close is too close when working near a tree or trees? It depends. To minimize damage, there are several recommendations and formulas that can be applied. They include:
Work with an ISA Certified Arborist to evaluate and make recommendations before construction begins.
To many contractors and equipment operators, trees are an obstacle they must work around.
Root preservation isn’t much of a consideration. Discuss with them ahead of time how important your trees are to you. Careful attempts must be made to minimize damage.
Take before, during and after pictures. Establish damage penalties should damage occur.
Some trees just can’t be saved and should be removed.
Some tree varieties are more tolerant of root severing and soil compaction than others.
Define construction zone boundaries. Put up fencing and Off-Limits signs.
Stay out from under the tree’s dripline, or at least 10 feet away from the tree.
By not cutting roots larger than 2 inches in diameter, and making clean cuts on damaged roots, you are giving a tree a fighting chance at survival.
Nitrogen fertilization is not recommended following root injury. Nitrogen benefits decay- causing organisms more than it does the tree.
Root damaged trees will require supplemental watering.
Mulching root damaged trees will provide many benefits.
I have briefly touched on this topic. A University publication titled “Protecting Trees from Construction Damage” is more detailed and contains a Tree Species Tolerance table.
By: Steven Pregler
ISA Certified Arborist