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Lead Article - Spring 2003 issue
Volume 29 Number 1
Tree Moving
Kerry Norman
The successful relocation of large trees is both a
remarkable and difficult feat. There is definitely an art to
it. Tree moving, which allows the addition of mature trees
to landscaping projects, has become a popular practice to
beautify or otherwise enhance large and small-scale
developments.
I have been involved with and have observed many successful
tree-moving projects where the relocated trees have
contributed significantly to the community for several years
now. Some people may, however, have a different opinion.
I've worked with and read the reports of those who argue
that tree relocation is generally a loosing proposition,
typically resulting in tree failure. One of these field
studies included trees that initially lacked vigor and
vitality. Some had experienced heavy fire damage while boxed
in the field and most suffered a lapse in care for a period
of approximately one year. These circumstances clearly do
not provide adequate grounds to arrive at a reasonable
conclusion that tree relocation can be dismissed as a means
of preserving heritage trees from condemnation due to
development.
Although tree relocation is a complicated and risky
prospect, it can usually be performed successfully. My
experience is that if you start with a healthy tree, box it
correctly and at the right time and provide adequate
maintenance, you can expect a high rate of success.
There are only a handful of tree moving companies in the
United States that are capable of moving large specimen
trees with root balls in excess of 10 feet in diameter. I
was the staff arborist for one of these companies for six
years. During this time, I evaluated trees for their
potential to survive relocation, and supervised their care
before, during and after. I also made regular site
inspections on many projects for up to five years following
tree relocation to diagnose problems and to evaluate our
tree moving procedures and maintenance practices. Based on
this experience, I will be discussing several topics
significant to tree moving. This article focuses primarily
on the relocation of Quercus agrifolia. I have been involved
with many tree relocations projects, both large and small,
involving residential, commercial and golf course
development and community redevelopment projects. The
following information and opinions is based on more than six
years of observations and hands-on experience working with
the relocation of mature trees.
Defining a Good Candidate
The first step in tree relocation is to conduct a
comprehensive inspection of the tree and site to determine
the likelihood of it surviving and thriving following
relocation. The tree must be healthy and vigorous, showing
no indications of stress. Structural integrity is also
critical because many trees are relocated from oak woodlands
to areas of high traffic where hazard potential is a
definite concern.
Trees must be thoroughly inspected for the signs and
symptoms of significant insect pests and diseases. Look for
structural problems, e.g., included bark, girdling roots,
cracks, cavities and decay in the trunk and branches. Tree
species must also be considered, as there are several that
do not respond well to relocation.
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Arbutus unedo- This tree was relocated approximately 5 years ago. It was put into a 20' box. The tree continues to perform and is clearly an asset to the property. |
Quercus agrifolia - This job consisted of relocating 12 trees. The work was performed approximately 10 years ago. It is clear to see they are doing well. |
Box Size
Determining the adequate box size for a particular tree
requires a great deal of experience and knowledge.
Considerations include, but are not limited to, species,
trunk diameter, canopy size, structure, size of roots and,
of course, site conditions. The ISA standard for determining
container size is approximately nine inches (diameter) of
root ball to each inch of trunk diameter. Most tree
companies, however, allow only about seven inches of root
ball per inch of trunk diameter. To be competitive,
tree-moving companies are forced to take this to the extreme
by putting trees in comparatively small boxes. While some
tree species may survive with smaller root balls than
recommended, others species are very sensitive to box size.
On the more sensitive species, I recommend using the largest
box allowable considering the project budget. The greater
the root mass the greater the likelihood of success.
Preparation
Removing a major portion of the root system during the
boxing process effectively induces drought stress. Although
not a generally accepted practice, I'm convinced that
drought stress in trees to be relocated can be significantly
reduced by thoroughly irrigating them 2-3 times within a two
to three-week period prior to any root pruning or
excavation. This allows the tree to take up ample water for
storage, which will help maintain normal life-processes,
allowing roots to regenerate. This important step should be
especially helpful during periods of drought. The use of
pesticides to prevent insect attack or disease development
may also be beneficial in preparation and is discussed later
in this article. Marking the trees orientation is also an
important reference when replanting. It is preferable to
replant a tree in its original orientation; primarily to
reduce the risk of sunscald to the bark and to minimize the
expenditure of stored energy to re-acclimate to the new
orientation.
Pruning
The negative response in trees to pruning prior to
relocation has been very clear to me. When I first began
working in this field, it was common practice to prune
heavily, often I would see more than 50 percent of canopy
removed prior to boxing. At the time, I had just become a
Certified Arborist and was anxious to improve on the
process. I knew from basic tree biology that heavy foliage
removal, which has a negative impact on tree health, would
only add to the stress of severe root loss. Provided they
receive adequate care, trees will respond naturally to root
loss by shedding leaves (abscission) and/or branches as
needed. Foliage is necessary for energy production
(photosynthesis) and the manufacture of hormones; both of
which are critical for root regeneration. It didn't take
long to convince company managers to reduce pruning to a
minimum, only dead, dying, diseased or structurally weak
branches. Prior to this procedural change, relocated trees
typically took several years or more to recover. With the
new pruning practices in place, I noticed a remarkable
change in how the trees responded to boxing and relocation.
It appeared that defoliation was significantly reduced and
that roots regenerated more quickly. Other advancements have
been made in tree relocation over the past few years, but
none I've seen have been as significant as minimizing
pruning.
Fertilization, Supplements and Soils
I have seen little in the way of fertilizers or supplements
that provide a noticeable or significant difference in the
survival of relocated trees during the critical period, 30
to 60 days after boxing. I believe, and there is a general
consensus within the industry, that fertilization and the
use of certain supplements applied during the maintenance
phase after this critical period can influence tree
performance and long-term survival. Although, I have tried
many of the so called,miracle products, I have yet to
witnessed a miracle. I have also inoculated several trees
using various forms and applications of mycorrhizae, but
have not noted any observable change in survival or
performance in the treated trees. I believe that if a tree
is healthy prior to relocation, soil nutrient levels are
adequate and that the native mycorrhizae are present.
However, when a tree is relocated to another site where soil
conditions may be unfavorable or nearly sterile due to
excavation, loss of topsoil, etc., mycorrhizae and certain
amendments may be useful, based on a soil analysis.
According to ISA standards, amending the backfill soil for
tree planting is generally not recommended, however, should
a soil analysis reveal toxicity or deficiencies, corrective
measures are appropriate. When dealing with soils of varying
texture and structure, consideration must be given to water
percolation, water-holding capacity, drainage and aeration,
as irrigation practices may affect survival and
performance.
Cabling/Guy Wires
Stabilizing trees during the establishment period to prevent
toppling is an extremely important topic when discussing
tree relocation , it can determine success or failure. In
addition, a falling tree may affect others nearby.
Obviously, root anchorage is severely compromised during the
boxing process, and for this reason all relocated trees
should be guy wired. Typically, one considers installing
cables after planting, however, it is equally important to
consider stability during boxing, transporting and planting
trees. It is advisable to provide temporary guy wires during
these procedures. My experience is that cables must remain
in place for no less than two years and in some cases up to
five years. Maintenance of cables plays a vital role in the
success and safety of tree moving. Proper cable installation
and maintenance insures the safety of people, property and
the tree as well.
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Close up of current years shoot growth, some in excess of 9". |
These two photos are shown in rebuttal to an article published in SCOPE (Santa Clarita organization for planning the community) in 2002, the article can be visited at (www.scope.org/welcome.html). The writer claims that the Quercus lobata is failing due to being moved. The photos I shot were taken in April 2003 of the same exact tree and it is again clear the tree is far from dead. |
Planting
The planting of relocated trees is fairly straightforward.
When working with large trees remember to install guy wires
during planting to reduce the risk of the trees toppling.
The planting pit dimensions will normally be one to three
feet larger than the root ball and up to six inches
shallower than root ball depth. Amending the backfill soil
is seldom necessary except to correct specific problems
determined by a soil analysis. The compaction of backfill is
very important; it not only increases stability but also
affects irrigation efficiency by eliminating air pockets.
Irrigation water can collect in large air pockets, bypassing
the root ball. It is advisable to install a drainage system
in all planting pits, with the exception of those where
excess water can freely drain away, e.g., sandy soil, slopes
or mounds.
Maintenance and Irrigation
These two procedures, I believe, are the most critical
factors in the success and survival of relocated trees.
Trees are particularly sensitive to soil moisture levels,
following the loss of often more than 80 percent of the root
system. The need for supplemental water greatly increases
due to the reduced capacity of the remaining root system to
absorb water. Initially, the root ball soil provides the
only reservoir for water until the roots begin to grow into
the native soil. Trees that usually survive without water
for long periods now require regular and frequent
irrigation, resulting in an increased risk of soil
pathogens. A fine balance between soil that is too wet and
too dry must be maintained. This can only be achieved by
regularly scheduled servicing by experienced staff, usually
supervised by a certified arborist. Although the practice of
irrigating a tree may sound simple, great care and effort is
required to insure proper soil moisture. It is imperative to
check soil moisture by using a soil probe before and after
watering to determine how much water if any to add.
"Monitoring of soil moisture can be scheduled, the actual
irrigation cannot". Two of the most common problems are over
or under watering.
In my opinion, the most serious threat to the survival of
relocated trees is over-watering. I would rather see
irrigation error on the drier side. Over-watering usually
occurs when the tree is either planted below grade or the
soil grade has been increased around the tree. These
conditions frequently result in serious problems. Other
conditions that are associated with over-watering include
broken irrigation lines, planting in poorly drained soil and
at the base of a slope. Under- watering most often occurs
when the irrigation water does not percolate readily into
the root ball, this most commonly happens as water runs over
the top of the root ball and into the backfill.
Consequently, the soil within the root ball remains dry
because the water in the backfill does not move readily into
the root ball. Soil watering basins must be maintained just
inside the edge of the tree root ball to ensure percolation.
Mulching, which reduces soil temperature and helps conserve
soil moisture, is conducive to new root growth as newly
developed fine roots are highly susceptible to
desiccation.
One of the key pitfalls related to maintenance is that
contractors, developers, homeowner's etc., rarely budget for
post-relocation tree care. Problems requiring immediate
corrective action are likely to develop without a
maintenance program and regular monitoring. It may be too
late by the time someone recognizes the problem. I've found
that about 70 percent of the failures in relocating trees
are attributable to inadequate maintenance. Adverse site
conditions, construction-related problems and undetermined
causes are responsible for the other failures.
Pest and Disease Problems
Root loss associated with tree relocation causes stress,
increasing susceptiblity to certain insect and disease
pests. Careful monitoring for the signs and symptoms of
developing pest problems is needed to prevent or minimize
such problems. When dealing with pest problems "the best
defense is a good offense". It is preferable to prevent
problems than to have to deal with them later, hence,
careful evaluation and selection, preparation, timing and
follow-up care are critical. Some pest and disease issues
are best managed by using appropriate chemicals as a
prophylaxis. This is especially true in the prevention of
bark boring insects. As mentioned earlier, trees undoubtedly
become stressed during relocation; therefore preventative
measures must be taken. The most common disease problem
encountered in relocated trees is "Phytophthora" , a root
and root crown disease of trees associated with poor
drainage and over-watering. Although fungicidal treatment
may be useful, the best way to manage phytophthora is
through careful irrigation practices. Although, other
insects and diseases may be noted, only a handful can
actually threaten the health and survival of relocated
trees. Chemical treatment should be reserved for serious
problems.
Reestablishment
As stated earlier, my remarks regarding responses to
relocation are relevant primarily to Quercus agrifolia. The
reestablishment period of relocated trees varies widely
among species. Trees reestablish their root to shoot balance
by first regenerating root at the expense of shoot growth.
Therefore, some trees may have a period of reduced aesthetic
quality. This period can be short providing that the tree
was healthy and vigorous initially. My experience is that a
minimum of two years or longer is required for
reestablishment. This is contingent upon a closely
supervised maintenance program. After approximately two
years, maintenance demands greatly decrease, reducing tree
care costs. Trees that have been relocated will require some
maintenance and monitoring for the remainder of their lives,
however requirements continue to diminish as time passes. At
the very least, it is recommended that relocated trees be
evaluated by an experienced certified arborist no less that
3-4 times a year.
Conclusion
I have been involved with several projects that include the
relocation of Quercus agrifolia in box sizes up to 18 feet.
On many of these projects more than 10 years has elapsed
since the trees were moved, and they have performed
beautifully and continue to show vigor. In more recent
years, with greater experience and industry innovations some
trees seem to hardly miss a beat when relocated. I attribute
these successes to proper selection, preparation, proper
pruning, and adequate follow up maintenance.
Tree moving is a big investment and should not be taken
lightly. Not only is the relocation process costly, but also
long-term maintenance and monitoring must be factored into
the budget. There are obviously risks involved with
relocation and some trees are poor candidates. In my
opinion, tree relocation should be considered as a last
resort, it is always best when a tree can remain
undisturbed. Tree moving has saved many trees to the benefit
of countless communities. Landmark heritage and specimen
trees can be spared when it is necessary to make way for
development.
Kerry Norman
Certified Arborist
Western Chapter International Society of Arboriculture
235 Hollow Oak Drive, Cohasset, CA 95973
Phone: (530) 892-1118
FAX: (530) 892-1006