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Prune Before Monsoon
Andrew Backhaus, Ph. D. Artistic Arborist Inc.
4519 N. 7th Ave, Phoenix, AZ 85013
Monsoons = Tree Damage
The most serious damage to our landscape trees occurs during monsoon season,
when high winds cause tree's to be uprooted and limbs to crash into power lines
and trees. The economic damage is incredible. To minimize damage to your trees
and home it is vital to have your trees pruned correctly. Unfortunately much of
the damage to our properties is the result of poor pruning which sets up
structural weaknesses in our threes and makes them potential hazards. We can
divide the problems into to two major categories, structural tree crown problems
and root problems.
 Above are example
of poor pruning and tree management practices
The Key to Good vs. Bad Tree Crown Structure is Balance
A good crown has good balance. Stand back and look at the tree. If the
trunk has a visible lean or one side of the crown has an abundance of limbs on
one side and an absence of limbs on the other, it becomes obvious that such a
tree may be predisposed to falling over.
Balance Between Top and Bottom of the Crown
Less obvious is the imbalance between the top and the bottom of the tree crown.
Here is were we see a lot of problems created by bad pruning, because most
untrained "tree trimmers" tend to remove most of the wood that's closest too the
ground. This causes the trees to be top heavy, and creating a sail that traps
high wind and causes tree limb failure. We find many trees pruned this way, and
it does create a hazard. Often the trunks and scaffold limbs are shaved of all
small interior branches which causes undue structural stress on the limb. A
simple test, use your arm to push up on the limb in excess of 6" in diameter and
at least 10' long. If it moves up and down easily, like a teeter totter, it
means excess counter weight on the branch ends and it is a candidate for limb
failure. This happened because when the small interior branches were removed, it
prevented the limb from tapering. The counter weight at the end of the limb, was
left unpruned and caused the imbalance. In our practice we have seen extreme
situations where fat 16" diameter limbs extending out 25' could be moved with a
finger. This is a dangerous situation.
'V' vs. 'L' Branch Angles
Another vital structural characteristic is angle of attachment of large interior
branches. Remember, the strongest angles are wide angles. In general a 'V' is
weaker than an 'L' angle. When trees are pruned to improve structure, the 'L'
branches should be favored over the 'V'. Frequently on mesquites, we'll see 'V'
limbs that split from the trunk. Make sure the arborist you hire understands the
difference. If he doesn't, he hasn't been trained properly. In the case were a
'V' attachment is vital for the tree, such as mature trees or trees where the
'V' maintains upper crown balance, in say a eucalyptus, then it is important to
consider having those limbs cabled or braced. Hire a trained arborist who knows
where to install the lag bolts that hold the limbs in place. Proper cabling will
allow the limbs to sway and "give" in the wind. They are not intended to hold
the limbs rigidly in place, but rather prevent those limbs from crashing into
the ground or house in case they do fail. Corrective pruning to lighten the end
weight of your limbs is the best insurance against limb failure.
Avoid Dangerous Situations
The tree above shows a power line entering the tree crown, a
potentially hazardous situation, especially in monsoon season. Find a skilled
arborist to have such trees thinned out to minimize the hazard.
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| Trunk above has
good taper and good root flare |
Trunk above has no taper and no
root flare |
Root Structure - A Key to Holding Your Tree Up
As with the crown, a tree's root system also needs balance. The key indicator is
good root flare. The base of the tree trunk should flare out and have a shape
like this ® ∆, not this ®
l
(see diagram above.) A tree must
have good taper to be withstand wind storms. This taper must be visible all around the
trunk, not just on one side. Lack
of taper indicates structural root problems with girdling or kinking roots below the soil
or a tree that was planted too deep. Trees with poor taper have a greater potential
to blow over in winds. Often times, after severe wind storms, blown down trees
will reveal severe cork-screw root systems that too weak to hold up the heavy
tree crown. If your trees show signs of these kinds of conditions, better have
your
arborist do a crown weight/size reduction, especially before the monsoon season.
It's also a good idea to not irrigate your trees too heavily, as wet soils tend
to destabilize trees with weak root systems compared to dry soils.
These are a few guidelines to follow for the upcoming monsoon season. If you
suspect you have a potential problem, call Artistic Arborist to schedule a
visit. Remember, tree doctors do make house calls. The pruning experts in our
service department can also do the necessary structural pruning to make your
trees safer and healthier.
© 2003-2005 Artistic-arborist.com, Inc. All
rights reserved.
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