Reprinted from:
City Trees: Journal of the Society of Municipal Arborists
www.urban-forestry.com
July 2007
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Calabash
tree (Crescentia cujete) arrow indicate 5 yr old compression
damage. |
Recently I visited
a job site where large tropical specimen trees had been relocated two
years ago, a year before construction began. I know the trees were properly
moved by competent professionals, because I met the team and was able
to observe the trees immediately after the move. What surprises me now
when I visit the site is the amount of damage to the trees that has occurred
since the relocation.
Hiring experienced professionals
to relocate specimen trees is very important to the ultimate survival
of those trees. What is just as important, or perhaps even more so, is
the pre-relocation and post-relocation care of the trees. The pre-relocation
care ensures that the trees are in the best condition, have recovered
and responded well to the root pruning, and are ready to be relocated.
The post-relocation care is perhaps the most critical time of the move.
At this time, the tree is under stress and will not be able to respond
to damage in the same manner as it would in its most healthy and vigorous
state.
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Bo
Tree (Ficus religiosa) arrow indicates 5 yr old compression
damage from a tree strap. Aerial roots on the Bo tree began to grow
over the damage two years ago and are now being trained to a pole
to create an extra trunk for stabilization during hurricanes. |
I recognize that the
key to all of this is the bottom line—the budget and those that
are in charge of the budget. But most owners and developers are not aware
that their costly investment in the relocation of specimen trees is not
necessarily assured without long-term care. Often “value engineering,”
or cost reduction, interferes with the long-term care that is necessary
to the survival of these trees.
Pre-relocation Care
Root-pruning by backhoe is much cheaper than root-pruning by hand, but
the results are never the same. The danger of pulling and tearing out
roots at the trunk using a large piece of equipment is high, and the resulting
damage to the trunk can be fatal. When roots have been torn away from
the trunk, rot will likely occur. My observation—and this includes
palm trees—has been that even if the rot is compartmentalized in
time, the tree may become structurally unsound and hazardous.
I always suggest root pruning
by hand to ensure roots are cut cleanly. Roots compartmentalize damage
the same way as branches and trunks, and they require a clean cut. In
addition, do not let the tree dry out. Make sure the roots of the tree
are irrigated on a regular basis and just before relocation. A moist root
ball is heavier—thereby requiring larger equipment—but will
be better equipped to survive the relocation.
Methods of
Moving Large Tropical Trees
There are three primary methods for relocating trees: building a container
around the root system and picking it up; pinning the tree by drilling
a hole through the trunk and inserting a steel pin that will be utilized
as a pick-up point; or rigging the branches and/or trunk with straps.
In my opinion, picking up root containers is the best way to move large
trees. Expense is the major disadvantage.
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Black
Olive (Bucida buceras) arrow indicates 5 yr old compression
damage. |
One advantage of the
second method, pinning the trunk, over straps is that the branches do
not have to bear the stress of picking up the tree. However, we know that
wounds close—they don’t heal. The wood that was exposed to
the drill and any stressed wood surrounding the pin will never be restored
to its original health. One hopes for optimum compartmentalization by
the tree’s natural immune system so fungi and pathogens can’t
spread very far into sound wood, but there is the possibility that the
tree will become hazardous in time.
The third method, strapping
a tree trunk or several branches for pickup, is perhaps the most common
(and cheapest) method of rigging large trees for moving. I have seen trees
weighing up to 80 tons picked up by the branches (in this instance, at
four points) and eventually recover and thrive in their new location.
There is a problem, however: trunk compression from the strap.
Different species of tropical
trees react differently to trunk compression. In some cases,
I attribute immediate damage to poor rigging, but some species simply
do not tolerate straps, especially over a certain total tree weight. Other
species seem to resist compression from strapping initially—the
bark is intact when the straps come off—but show damage two to three
years later. Depending on the tree species and the way it was strapped,
this damage can result in rot and disease in the main trunk and/or total
branch loss.
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This
arjuna tree (Terminalia arjuna) was moved two years ago, the arrow
shows the resulting compression damage from tree straps. |
Post-relocation
Care
Large specimen tropical trees can be relocated successfully, but the horticultural
care required in the subsequent two years is critical. Trees are very
vulnerable on construction sites due to equipment damage and soil compaction.
Also, when trees are moved onto active construction sites, they are sometimes
planted at a higher grade until construction is completed and the surrounding
grade is raised. Those trees, basically planted on a mound, can dry out
fast. In tropical areas or any area with high temperatures, keeping the
root ball well irrigated can be very difficult. But if a newly planted
tree keeps drying out, stress will be a constant factor, and insects and
other pathogens will have a better opportunity to attack the tree.
When working in areas prone
to hurricanes or typhoons, braces and other supports must be removed just
before the winds hit, so the tree can blow over unencumbered. I have observed
that if the braces or stakes are left on, trees may snap off. But among
tropical trees, blow-downs can be promptly replanted and often recover
well.
The cost involved in the relocation
of a large tree can be substantial. But the alternative, if “value
engineering” wins the day, is more costly: at least, wasted effort
and at worst, a hazardous tree that could eventually cause damage to life
and property.
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The
arrow show the hole where a steel pin was inserted through the trunk
of a kepoh tree (Sterculia foetida) two years ago. Also
shown are nails that have been hammered into the tree to attach
braces. Cambial dieback and rot are likely due to these deep holes
in the trunk-a potential hazard tree even with the callus forming
around the larger hole. |
Relocated
five years ago with rigging from three tree straps, this kamani
tree (Calophyllum inophyllum) shows the kind of damage
that can occur from trunk compression. The arrow shows where the
strap was attached and compression occured. The entire trunk will
have to be removed. |
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 |
This
seagrape (Coccoloba uvifera) was relocated five years ago
by tree strap without any trunk or branch damage. |
More
than 100 tropical trees at Parrot Jungle Island were successfully
relocated five years ago, including Bo tree (Ficus religiosa),
kamani (Calophyllum inophyllum), and black olive (Bucida
buceras). Some strap damage occurred, but pre- and post-planting
care ensured successful establishment. |
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