Topping is perhaps the most harmful tree pruning practice
known. Yet, despite more than 25 years of literature and seminars explaining
its harmful effects, topping remains a common practice.
What is Topping?
Topping is the indiscriminate cutting of tree branches to
stubs or to lateral branches that are not large enough to assume the terminal
role. Other names for topping include “heading,” “tipping,” “hat-racking,” and
“rounding over.”
Topping is often used to reduce the size of a tree. A
homeowner may feel that a tree has become too large for his or her property, or
that tall trees may pose an unacceptable risk. Topping, however, is not a
viable method of height reduction and certainly does not reduce future risk. In
fact, topping will increase risk in the long term.
Topping Stresses Trees
Topping can remove 50 to 100 percent of a tree’s
leaf-bearing crown. Leaves are the food factories of a tree. Removing them can
temporarily starve a tree and trigger various survival mechanisms. Dormant buds
are activated, forcing the rapid growth of multiple shoots below each cut. The
tree needs to put out a new crop of leaves as soon as possible. If a tree does
not have the stored energy reserves to do so, it will be seriously weakened and
may die.
A stressed tree with large, open pruning wounds is more
vulnerable to insect and disease infestations. The tree may lack sufficient
energy to chemically defend the wounds against invasion, and some insects are
actually attracted to the chemical signals trees release.
Topping Leads to Decay
Correct pruning cuts are made just beyond the branch collar
at the point of attachment. The tree is biologically equipped to close such a
wound, provided the tree is healthy enough and the wound is not too large. Cuts
made along a limb between lateral branches create stubs with wounds that the
tree may not be able to close.
The exposed wood tissues begin to decay. Normally, a tree
will “wall off,” or compartmentalize, the decaying tissues, but few trees can
defend the multiple severe wounds caused by topping. The decay organisms are
given a free path to move down through the branches.
Topping Can Lead to
Sunburn
Branches within a tree’s crown produce thousands of leaves
to absorb sunlight. When the leaves are removed, the remaining branches and
trunk are suddenly exposed to high levels of light and heat. The result may be
sunburn of the tissues beneath the bark, which can lead to cankers, bark
splitting, and death of some branches.
Topping Can Lead to
Unacceptable Risk
The survival mechanism that causes a tree to produce
multiple shoots below each topping cut comes at great expense to the tree.
These shoots develop from buds near the surface of the old branches. Unlike
normal branches that develop in a socket of overlapping wood tissues, these new
shoots are anchored only in the outermost layers of the parent branches and are
weakly attached.
The new shoots grow quickly, as much as 20 feet (6 m)in one
year in some species. Unfortunately, the shoots are prone to breaking,
especially during windy or icy conditions. While the original goal was to
reduce risk by reducing height, risk of limb failure has now increased.
Topping Makes Trees
Ugly
The natural branching structure of a tree is a biological
wonder. Trees form a variety of shapes and growth habits, all with the same
goal of presenting their leaves to the sun. Topping removes the ends of the
branches, often leaving ugly stubs. Topping destroys the natural form of a
tree. Without leaves (for up to six months of the year in temperate climates),
a topped tree appears disfigured and mutilated. With leaves, it is a dense ball
of foliage, lacking its simple grace. A tree that has been topped can never
fully regain its natural form.
Topping Is Expensive
The cost of topping a tree is not limited to only the job
cost. Some hidden costs of topping include:
• Increased maintenance costs. If the tree survives, it will
likely require corrective pruning within a few years (e.g., crown reduction or
storm damage repair). If the tree dies, it will have to be removed.
• Reduced property value. Healthy, well-maintained trees can
add 10 to 20 percent to the value of a property. Disfigured, topped trees are
considered an impending expense.
• Increased liability potential. Topped trees may pose an
unacceptable level of risk. Because topping is considered an unacceptable
pruning practice, any damage caused by branch failure of a topped tree may lead
to a finding of negligence in a court of law.
Alternatives to Topping
Sometimes a tree must be reduced in height or spread, such
as for providing utility line clearance. There are recommended techniques for
doing so. Small branches should be removed back to their point of origin. If a
larger limb must be shortened, it should be pruned back to a lateral branch
that is large enough (at least one-third the diameter of the limb being
removed) to assume the terminal role. This method of branch reduction helps to
preserve the natural form of the tree. However, if large cuts are involved, the
tree may not be able to close over and compartmentalize the wounds. Sometimes
the best solution is to remove the tree and replace it with a species that is
more appropriate for the site
