| |
Proper pruning is essential in
developing a tree with a strong structure and desirable form. Trees that
receive the appropriate pruning measures while they are young will require
little corrective pruning when they mature.
There are a few simple principles that everybody should
understand before they set out to prune a tree.
• Each cut has the potential to change the growth of
the tree. Always have a purpose in mind before a cut is made.
• Proper technique is essential. Poor pruning
can cause damage that lasts for the life of the tree. Learn where and how to
make the cuts before picking up the pruning shears.
• Trees do not heal the way people do. When a
tree is wounded it must grow over and compartmentalize the wound. As a
result, the wound is contained within the tree forever.
• Small cuts do less damage to the tree than large
cuts. This is why proper pruning (training) of young trees is
critical. Waiting to prune a tree when it is mature can create the need for
large cuts that the tree cannot easily close.
Making The Cut
Where you make a pruning cut is critical to a tree's
response in growth and wound closure. Pruning cuts should be made just
outside the branch collar. Since the branch collar contains trunk or parent
branch tissues, the tree will be damaged unnecessarily if you remove or
damage it. In fact, if the cut is large, the tree may suffer permanent
internal decay from an improper pruning cut.
If a permanent branch is to be shortened, cut it back to a lateral branch or
bud. Internodal cuts, or cuts made between
buds or branches, may lead to stem decay, sprout production, and misdirected
growth.
Pruning Tools
When pruning trees, it is important to have the right tool
for the job. For small trees, most of the cuts can be made with hand pruning
shears (secateurs). The scissor type, or
by-pass blade hand pruners, are preferred over the anvil type. They make
cleaner, more accurate cuts. Cuts larger than 1/2 inch in diameter should be
made with lopping shears or a pruning saw.
Never use hedge shears to prune a tree. Whatever tool you use, make sure it
is kept clean and sharp.
Establishing a Strong Scaffold Structure
A good structure of primary scaffold branches should be
established while the tree is young. The scaffold branches provide the
framework of the mature tree. Properly trained young trees will develop a
strong structure that will require less corrective pruning as they mature.
The goal in training young trees is to establish a strong trunk with sturdy
well-spaced branches. The strength of the branch structure depends on the
relative sizes of the branches,  the
branch angles, and the spacing of the limbs. Naturally, this will vary with
the growth habit of the tree. Pin oaks and sweetgums, for example, have a
conical shape with a central leader. Elms and live oaks are often
wide-spreading without a central leader. Other trees, such as lindens and
Bradford pears, are densely branched. Good pruning techniques remove
structurally weak branches while maintaining the natural form of the tree.
Trunk Development
For most young trees, maintain a single dominant leader. Do
not prune back the tip of this leader. Do not allow secondary branches to
outgrow the leader. Sometimes a tree will develop double leaders known as
co-dominant stems. These can lead to structural weaknesses, so it is best to
remove one while the tree is young.
The lateral branches contribute to the development of a sturdy well-tapered
trunk. It is important to leave some of these lateral branches in place,
even though they may be pruned out later. These branches, known as temporary
branches, also help protect the trunk from sun and mechanical injury.
Temporary branches should be kept short enough not to be an obstruction or
compete with selected permanent branches.
Back to Top
Permanent Branch Selection
Nursery trees often have low branches that may make the tree
appear well- proportioned when young, but low branches are seldom
appropriate for large growing trees in an urban environment. How a young
tree is trained depends on its primary function in the landscape. For
example, street trees must be pruned so that they allow at least 16 feet of
clearance for traffic. Most landscape trees only require about eight feet of
clearance.
The height of the lowest permanent branch is determined by the tree's
intended function and location in the landscape. Trees that are used to
screen an unsightly view or provide a wind break may be allowed to branch
low to the ground. Most large growing trees in the landscape must eventually
be pruned to allow head clearance.
The spacing of branches, both vertically and radially, in the tree is very
important. Branches selected as permanent scaffold branches must be
well-spaced along the trunk. Maintain radial balance with branches growing
outward in each direction.
A good rule of thumb for the vertical spacing of permanent branches is to
maintain a distance equal to 3% of the tree's eventual height. Thus, a tree
that will be 50 feet tall should have permanent scaffold branches spaced
about 18 inches apart along the trunk. Avoid allowing two scaffold branches
to arise one above the other on the same side of the tree.
Some trees have a tendency to develop branches with narrow angles of
attachment and tight crotches. As the tree grows, bark can become enclosed
deep within the crotch between the branch and the trunk. This is called
included bark. Included bark weakens the attachment of the branch to the
trunk and can lead to branch failure when the tree matures. You should prune
branches with weak attachments while they are young.
Avoid over-thinning the interior of the tree. The leaves of each branch must
manufacture enough food to keep that branch alive and growing. In addition,
each branch must contribute food to grow and feed the trunk and roots.
Removal of too many leaves can starve the tree, reduce growth and make the
tree unhealthy. A good rule of thumb is to maintain at least half the
foliage on branches arising in the lower 2/3 of the tree.
Newly Planted Trees
Pruning of newly planted trees should be limited to
corrective pruning. Remove tor n or broken branches, and save other pruning
measures for the second or third year.
The belief that trees should be pruned when planted to compensate for root
loss is misguided. Trees need their leaves and shoot tips to provide food
and the substances which stimulate new root production. Unpruned trees
establish faster with a stronger root system than trees pruned at the time
of planting.
Wound Dressings
Wound dressings were once
thought to accelerate wound closure, protect against insects and diseases,
and reduce decay.
However, research has shown that dressings do not reduce decay or speed
closure and rarely prevent insect or disease infestations. Most experts
recommend that wound dressing not be used. If a dressing must be used for
cosmetic purposes, use a thin coating of a material that is not toxic to the
plant.
Back to Top
|
Pruning Mature Trees
reprinted with permission from the ISA web site
http://www.treesaregood.com/treecare/pruning_mature.asp
|
|
Pruning is the most
common tree maintenance procedure. Although forest trees grow quite well
with only nature's pruning, landscape trees require a higher level of
care to maintain their safety and aesthetics. Pruning should be done
with an understanding of how the tree responds to each cut. Improper
pruning can cause damage that will last for the life of the tree, or
worse, shorten the tree's life.
Reasons for Pruning
Since each cut has the potential to change the growth of
the tree, no branch should be removed without a reason. Common reasons
for pruning are to remove dead branches, to remove crowded or rubbing
limbs, and to eliminate hazards. Trees may also be pruned to increase
light and air penetration to the inside of the tree's crown or to the
landscape below. In most cases, mature trees are pruned as a corrective
or preventative measure.
Routine thinning does not necessarily improve the health of a tree.
Trees produce a dense crown of leaves to manufacture the sugar used as
energy for growth and development. Removal of foliage through pruning
can reduce growth and stored energy reserves. Heavy pruning can be a
significant health stress for the tree.
Yet if people and trees are to coexist in an urban or suburban
environment, then we sometimes have to modify the trees. City
environments do not mimic natural forest conditions. Safety is a major
concern. Also, we want trees to complement other landscape plantings and
lawns. Proper pruning, with an understanding of tree biology, can
maintain good tree health and structure while enhancing the aesthetic
and economic values of our landscapes.
When to Prune
Most routine pruning to remove weak, diseased, or dead
limbs can be accomplished at any time during the year with little effect
on the tree. As a rule, growth is maximized and wound closure is fastest
if pruning takes place before the spring growth flush. Some trees, such
as maples and birches, tend to "bleed" if pruned early in the spring.
This may be unsightly, but is of little consequence to the tree.
A few tree diseases, such as oak wilt, can be spread when pruning wounds
allow spores access into the tree. Susceptible trees should not be
pruned during active transmission periods.
Heavy pruning just after the spring growth flush should be avoided. This
is when trees have just expended a great deal of energy to produce
foliage and early shoot growth. Removal of a large percentage of foliage
at this time can stress the tree.
Back to Top
Making Proper Pruning Cuts
Pruning cuts should be made just outside the branch collar. The branch collar contains
trunk or parent branch tissue and should not be damaged or removed. If
trunk collar has grown out on a dead limb to be removed, make the cut
just beyond the collar. Do not cut the collar.
If a large limb is to be removed, its weight should first be reduced.
This is done by making an undercut about 12-18 inches from the limb's
point of attachment. A second cut is made from the top, directly above
or a few inches further out on the limb. This removes the limb leaving
the 12-18 inch stub. The stub is removed by cutting back to the branch
collar. This technique reduces the possibility of tearing the bark.
Pruning Techniques
Specific types of pruning may be necessary to maintain a
mature tree in a healthy, safe, and attractive condition.
Cleaning:
the removal of dead, dying, diseased, crowded, weakly attached, and
low-vigor branches from the crown of a tree.
Thinning:
the selective removal of branches to increase light penetration and air
movement through the crown. Thinning opens the foliage of a tree,
reduces weight on heavy limbs, and helps retain the tree's natural
shape.
Raising:
removes the lower branches from a tree in order to provide clearance for
buildings, vehicles, pedestrians, and vistas.
Reduction:
reduces the size of a tree, often for clearance for utility lines.
Reducing the height or spread of a tree is best accomplished by pruning
back the leaders and branch terminals to lateral branches that are large
enough to assume the terminal roles (at least 1/3 the diameter of the
cut stem). Compared to topping, this helps maintain the form and
structural integrity of the tree.
Back to Top
How Much Should Be Pruned?
The amount of live tissue that should be removed depends
on the tree size, species, and age, as well as the pruning objectives.
Younger trees will tolerate the removal of a higher percentage of living
tissue than mature trees. An important principle to remember is that a
tree can recover from several small pruning wounds faster than from one
large wound.
A common mistake is to remove too much inner foliage and small branches.
It is important to maintain an even distribution of foliage along large
limbs and in the lower portion of the crown. Over-thinning reduces the
tree's sugar production capacity and can create tip-heavy limbs that are
prone to failure.
Mature trees should require little routine pruning. A widely accepted
rule of thumb is never to remove more than 1/4 of a tree's leaf bearing
crown. In a mature tree, pruning even that much could have negative
effects. Removing even a single, large-diameter limb can create a wound
that the tree may not be able to close. The older and larger a tree
becomes, the less energy it has in reserve to close wounds and defend
against decay or insect attack. The pruning of large mature trees is
usually limited to the removal of dead or potentially hazardous limbs.
Wound Dressings
Wound dressings were once thought to accelerate wound
closure, protect against ins ects and diseases, and reduce decay.
However, research has shown that dressings do not reduce decay or speed
closure and rarely prevent insect or disease infestations. Most experts
recommend that wound dressings not be used. If a dressing must be used
for cosmetic purposes, then only a thin coating of a non-toxic material
should be applied.
Hire an Arborist
Pruning large trees can be dangerous. If pruning
involves working above the ground or using power equipment, it is best
to hire a professional arborist. An arborist can determine what type of
pruning is necessary to improve the health, appearance, and safety of
your trees. A professional arborist can provide the services of a
trained crew, with all of the required safety equipment and liability
insurance.
There are a variety of things to consider when selecting an arborist:
• Membership in professional organizations such as the International
Society of Arboriculture (ISA), the Tree Care Industry Association (TCIA),
or the American Society of Consulting Arborists (ASCA).
• Certification through the ISA Certified Arborist program.
• Proof of insurance.
• A list of references (Don't hesitate to check.)
• Avoid using the services of any tree company that:
- Advertises topping as a service provided. Knowledgeable arborists know
that topping is harmful to trees and is not an accepted practice.
- Uses tree climbing spikes to climb trees that are being pruned.
Climbing spikes can damage trees, and their use should be limited to
trees that are being removed.
Back to Top
|
| Thinning trees to withstand hurricanes, storms
By CHUCK LIPPI
Consulting Arborist
St. Augustine Record, Aug. 27, 2005
| Because of concern with wind
damage from hurricanes and tropical storms, many homeowners
are asking tree service companies to thin their trees. As
with most procedures, there is a right way to thin a tree
and a wrong way. Unfortunately, I see a lot of improper tree
thinning being done throughout Florida. Worse yet, improper
thinning can make trees more susceptible to wind damage.
Proper thinning is done by removing smaller branches
evenly throughout the tree canopy. Improper thinning removes
an excessive amount of branches and foliage from the
interior of the tree. In effect, removing interior branches
and foliage leaves a large percentage of the branch weight
out at the ends of the branch which puts additional stress
on the branch and increases the likelihood of failure in
storms.
The term used by some tree services is cleaning, which
implies something good is going to be done to the tree. Who
can turn down an offer to clean anything? Mom would be
proud. Those ugly and useless internal branches and sprouts
are going to be removed. I'll clean that tree up for you so
it looks real pretty, is the way I have often heard the
thinning service presented to customers. A more accurate
term for the procedure of removing interior branches is
stripping or lion tailing. 
Another problem with removing foliage and small interior
branches is reduced diameter growth of larger branches.
Remember leaves are the engine that powers tree growth and
health. Carbohydrates produced by leaves are deposited and
stored in the sapwood of nearby larger branches. Remove the
small interior branches and foliage and the large branch on
which they were growing will slow its increase in diameter
and be more prone to breakage.
Sprouts (called waterspouts by arborists) growing on
interior large branches are often described as ugly growth
that should be removed. But these sprouts are often the
result of over pruning, over-thinning and lion tailing.
Sprouts are the tree's attempt to replace foliage that had
been removed. Sprouts should be left in place for several
years. Then select the strongest sprouts to keep being sure
they are evenly spaced along the branch and train these
remaining sprouts as new branches. The rest of the sprouts
can be thinned. If too many sprouts are removed, they will
grow back, which means the tree is trying to tell you
something -- it has been over pruned. 
Another problem with lion tailing is one I encounter
often when giving advice to homeowners on proper pruning. If
a lion tailed branch must be reduced in size because it is
hazardous or is carrying too much weight, there is no crotch
to which the reduction can be made without cutting all the
way back to the trunk. Lion-tailed branches are difficult to
correct and repair with current acceptable pruning
techniques.
In general, do not remove more than about 15 to 20
percent of the live foliage on a mature tree at one time. If
possible, only remove 5 to 10 percent on mature trees. Less
pruning is always better than more pruning.
Based upon the latest research on tree structure and
observations of hurricane damage last year, we have a better
understanding what methods work best for tree safety as well
as what is best for the health of trees. Proper thinning is
not only better for a tree's wind resistance, but it is also
better for the tree's health. Tree wind resistance can vary
by tree species and the type and size of structural problems
that may be found in the trunk and branches.
|
| Back to Top |
|
|
|
|
