Trees can be
damaged or killed by a wide variety of construction activities. It's not
always easy to save trees, but your efforts will help. This document
describes measures to minimize construction impact.
First, protect roots that lie in the path of construction. Approximately
90 to 95 percent of a tree's root system is in the top three feet of soil,
and more than half is in the top one foot. Construction activities should
be avoided in this area. Protect as much of the area beyond the tree's
dripline as possible. Some healthy trees survive after losing half of
their roots. However, other species are extremely sensitive to root damage
even outside the dripline.
If possible, do
not disturb the Protected Root Zone (PRZ). The PRZ is defined by its
"critical root radius." It is more accurate than the dripline for
determining the PRZ of trees growing in forests or that have narrow growth
habits. To calculate critical root radius, measure the tree's diameter (dbh)
4.5 feet above the ground. Measure in inches. For each inch, allow for 1
to 1.5 feet of critical root radius. If a tree's dbh is ten inches, its
critical root radius is 10 to 15 feet.
CREATE A SUCCESSFUL LANDSCAPE PROTECTION PLAN:
Mark construction zone boundaries
at the edge of the protected root zone. Use
measuring tape, stakes and string to mark them.
Inventory trees on the site.
Record the location, size, and health of each tree. Trees that are
over mature, display poor form, lean heavily over buildings, or have
insect or disease problems should be removed prior to construction. Also
mark trees that need pruning.
Select the trees to be saved.
Note how each tree fits into the landscape. If the PRZ falls inside the
construction zone, seriously consider changing the original design,
adding protection measures or removing the tree before construction
Protect the trees you plan to save.
Develop a map while working with the builder showing the location of
trees to be protected and the safest route for access to the building
zone. Then install bright orange polypropylene fencing and post "Off
Limits" signs at the PRZ of the trees you plan to save. SOIL
COMPACTION IS ONE OF THE MOST COMMON KILLERS OF URBAN TREES.
Stockpiled materials, heavy machinery and excessive foot traffic damage
soil structure and reduces soil pore space. Roots suffocate.
Make sure all construction workers
know that nothing inside this area is to be disturbed.
A landscape protection contract will help ensure compliance. Take
several photographs of the site before construction begins.
Prepare trees for construction
disturbance. You'll boost your trees' chance
for survival if they're vigorous. Regularly water if rainfall is not
adequate. Fertilize if trees are nutrient stressed. Prune branches that
are dead, diseased, hazardous or detrimental to natural form.
Monitor the construction process.
Visit the site regularly and inspect the trees. Should damage occur,
begin repairs as soon as possible. Water trees throughout the
Make final inspection of the site.
After construction has been completed, evaluate the remaining trees.
Look for signs and symptoms of damage or stress. It may take several
years for severe problems to appear.
considerations during construction include site clearing, soil damage,
grade changes, soil excavation and pavement installation. Work with an
experienced professional urban forester or arborist, certified with the
International Society of Arboriculture.