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As cities and suburbs expand, wooded lands are being
developed into commercial and residential sites. Homes are
constructed in the midst of trees to take advantage of the
aesthetic and environmental value of the wooded lots.
Wooded properties can be worth as much as 20% more than
those without trees, and people value the opportunity to live
among trees.
Unfortunately, the processes involved with construction can
be deadly to the nearby trees. Further, unless the damage is
extreme, the trees may not die immediately but could decline
over several years. With this delay in symptom development,
you may not associate the loss of the tree with the
construction.
It is possible to preserve trees on building sites if the right
measures are taken. The most important step is to hire a
professional arborist during the planning stage. An arborist
can help you decide which trees can be saved, and can work
with the builder to protect the trees throughout each
construction phase.
How Trees Are Damaged During Construction
Physical injury to the trunk and crown
Construction equipment can injure the above-ground portion
of a tree by breaking branches, tearing the bark, and wounding
the trunk. These injuries are permanent, and if extensive, can
be fatal.
Cutting of roots
The digging and trenching that are necessary to construct a
house and install underground utilities will likely sever a
portion of the roots of many trees in the area. It is easy to
appreciate the potential for damage if you understand where
roots grow. The roots of a mature tree extend far from the
trunk of the tree. In fact, roots typically will be found growing a
distance of 1-3 times the height of the tree. The amount of
damage a tree can suffer from root loss depends, in part, upon
how close to the tree the cut is made. Severing one major root
can cause the loss of 5-20% of the root system.
The roots of a tree will extend far from the trunk and will be
found mostly in the upper 6 to 10 inches of the soil.
Another problem that may result from root loss due to digging
and trenching is that the potential for the trees to fall over is
increased. The roots play a critical role in anchoring a tree. If
the major support roots are cut on one side of a tree, the tree
may fall or blow over.
Less damage is done to tree roots if utilities are tunneled
under a tree rather than across the roots.
Soil compaction
An ideal soil for root growth and development is about 50%
pore space. These pores, the spaces between soil particles,
are filled with water and air. The heavy equipment used in
construction compacts the soil and can dramatically reduce the
amount of pore space. This not only inhibits root growth and
penetration but also decreases oxygen in the soil that is
essential to the growth and function of the roots.
Smothering roots by adding soil
Most people are surprised to learn that 90% of the fine roots
that absorb water and minerals are in the upper 6-12 inches of
soil. Roots require space, air, and water. Roots will grow best
where these requirements are met, which is usually very near
the soil surface. Piling soil over the root system or increasing
the grade will smother the roots. It only takes a few inches of
added soil to kill a sensitive mature tree.
Exposure to the elements
Trees in a forest situation grow as a community, protecting
each other from the elements. The trees grow tall with long,
straight trunks and high canopies. Removal of neighboring
trees or opening the shared canopies of trees will expose the
remaining trees to sunlight and wind. The higher levels of
sunlight may cause sunscald on the trunks and branches. Also,
the remaining trees will be more prone to breaking from wind
or ice loading.
Getting Advice
Hire a professional arborist in the early planning stage. Many
of the trees on your property may be saved if the proper steps
are taken. Allow the arborist to meet with you and your building
contractor. Your arborist can assess the trees on your
property, determine which are healthy and structurally sound,
and suggest measures to preserve and protect them.
One of the first decisions is determining which trees are to be
preserved, and which should be removed. You must consider
the species, size and maturity, location, and the condition of
each tree. The largest, most mature trees are not always the
best choices to preserve. Younger, more vigorous trees can
usually survive and adapt to the stresses of construction
better. Try to maintain diversity of species and ages. Your
arborist can advise you about which trees are more sensitive
to compaction, grade changes, and root damage.
Planning
Your arborist and builder should work together in planning the
construction. The builder may need to be educated regarding
the value of the trees on your property and the importance of
saving them. Few builders are aware of the way trees’ roots
grow and what is needed to protect them.
Sometimes small changes in the placement or design of your
house can make a great difference in whether a critical tree
will survive. An alternative plan may be more friendly to the
root system. For example, bridging over the roots may
substitute for a conventional walkway. Or, instead of trenching
beside a tree for utility installation, tunneling under the root
system is much less damaging.
Erecting Barriers
Because our ability to repair construction damage to trees is
limited, it is vital that the trees be protected from injury. The
single most important action you can take is to set up
construction fences around all of the trees that are to remain.
The fences should be placed as far out from the trunks of the
trees as possible. As a general guideline, allow one foot of
space from the trunk for each inch of trunk diameter. The
intent is not merely to protect the above-ground portions of
the trees but also the root systems. Remember that the root
systems extend much farther than the driplines of the trees.
Instruct the construction personnel to keep the fenced area
clear of building materials, waste, and excess soil. No digging,
trenching, or other soil disturbance should be allowed in the
fenced area.
Protective fences should be erected as far out from the trunks
as possible in order to protect the root system.
Limiting Access
If at all possible, it is best to allow only one access route on
and off the property. All contractors must be instructed where
they are permitted to drive and park their vehicles. Often this
same access drive will later serve as the route for utility wires,
water lines, or the driveway.
Specify storage areas for equipment, soil, and construction
materials. Limit areas for burning (if permitted), cement wash-
out pits, and construction work zones. These areas should be
away from protected trees.
Specifications
Get it in writing. All of the measures intended to protect your
trees must be written into the construction specifications. The
written specifications should detail exactly what can and
cannot be done to and around the trees. Each sub-contractor
has to be made aware of the barriers, limitations, and specified
work zones. It is a good idea to post signs as a reminder.
Fines and penalties for violations should be built into the
specifications. Not too surprisingly, sub-contractors are much
more likely to adhere to the tree preservation clauses if their
profit is at stake. The severity of the fines should be
proportional to the potential damage to the trees, and should
increase for multiple infractions.
Maintaining Good Communications
It is important to work together as a team. You may share clear
objectives with your arborist and your builder, but one sub-
contractor can destroy your prudent efforts. Construction
damage to trees is often irreversible.
Visit the site at least once a day if possible. Your vigilance will
pay off as workers learn to take your wishes seriously. Take
photos at every stage of construction. If any infraction of the
specifications does occur, it will be important to prove liability.
Final Stages
It is not unusual to go to great lengths to preserve trees
during construction, only to have them injured during
landscaping. Installing irrigation systems and rototilling
planting beds are two ways the root systems of trees can be
damaged. Remember also that small increases in grade, as
little as 2-6 inches, which place additional soil over the roots
can be devastating to your trees. Careful planning and
communicating with landscape designers and contractors is
just as important as avoiding tree damage during construction.
Post-Construction Tree Maintenance
Your trees will require several years to adjust to the injury and
environmental changes that occur during construction.
Stressed trees are more prone to health problems such as
disease and insect infestations. Talk to your arborist about
continued maintenance for your trees. Continue to monitor
your trees, and have them periodically evaluated for declining
health or safety hazards.
Despite the best intentions and most stringent tree
preservation measures, your trees may still be injured from the
construction process. There are remedial treatments that your
arborist can suggest to help reduce stress and improve the
growing conditions around your trees. In addition, the
International Society of Arboriculture offers a companion to
this brochure titled Treatment of Trees Damaged by
Construction
For Additional Information
This brochure is one in a series published by the International
Society of Arboriculture as part of its Consumer Information
Program.
Why Hire an Arborist
Tree Benefits
Tree Values
Tree Selection
Buying High Quality Trees
Avoiding Tree & Utility Conflicts
New Tree Planting
Mature Tree Care
Plant Health Care
Trees and Turf
Proper Mulching Techniques
Pruning Young Trees
Pruning Mature Trees
Why Topping Hurts Trees
Insect & Disease Problems
Avoiding Tree Damage During Construction
Treatment of Trees Damaged by Construction
