Discover why topping is not a good pruning technique and what alternatives are available.
Among tree pruning practices, topping is perhaps the most harmful. Even so, topping remains a common practice in spite of decades of literature and seminars describing its harmful effects.
The act of topping is the indiscriminate cutting of branches to stubs or to lateral branches that are not large enough to play the terminal role. A number of other terms have been used, including "heading," "tipping," "hat-racking," and "rounding."
Tree topping is often used to reduce the size of a tree. It is common for homeowners to see large trees as a threat to their property. However, topping is not an effective method of reducing height and may increase risk in the future. Trees depend on their leaves for food, but topping can remove 50-100% of their leaf-bearing crowns.
The removal of leaves can potentially starve the tree and trigger its survival mechanisms. As a result, dormant buds are activated, resulting in rapid growth of multiple shoots below each cut. A new crop of leaves must be produced as soon as possible.
In the absence of stored energy reserves, a tree will be seriously weakened and may even die. Stressed trees with large, open pruning wounds are more susceptible to insect and disease infestations. Insects are actually attracted to the chemical signals trees release because they lack sufficient energy to chemically defend the wounds.
There are thousands of leaves produced by branches within a tree's crown to absorb sunlight. By removing the leaves, the remaining branches and trunk are suddenly exposed to a high level of light and heat. It may cause sunburn to the tissues underneath the bark, resulting in cankers, bark splitting, and branch death.
During each topping cut, trees develop multiple shoots as a survival mechanism. Buds grow near the surface of old branches to form these shoots. The new shoots are weakly attached to the parent branches and do not develop in a socket of overlapping wood tissues like normal branches.
Some species have new shoots that grow as much as 20 feet (6 meters) in one year. In windy or icy conditions, shoots are prone to breaking due to a weak attachment. In spite of the original goal of reducing risk by reducing height, limb failure risk has now increased.
Trees lose their natural form when they are topped. Despite their variety of shapes and growth habits, trees all have the same goal: to present their leaves to the sun. It often leaves ugly stubs after topping the branches. The natural shape of a tree that has been topped can never be fully regained.
In order to prune properly, cuts should be made just beyond the branch collar. Trees can naturally close wounds of this size if they are healthy enough and they are not too large. A stub or wound created by indiscriminately cutting between lateral branches may not be closed by the tree. Decomposition begins in the exposed wood tissues. It is usually possible for trees to "wall off," or compartmentalize, decaying tissues, but many trees are not able to protect themselves from multiple severe wounds caused by topping. As a result, decay organisms can move freely through the branches.
There is more to the cost of topping a tree than just the job cost. Here are a few hidden costs:
An increase in maintenance costs. Within a few years, the tree will likely require corrective pruning (e.g., crown reduction or storm damage repair). In the event that the tree dies, it will have to be removed.
A decrease in property value. Having healthy, well-maintained trees can add 10-20% to a property's value. Trees that have been disfigured or topped are considered an impending expense.
Starved" trees - Topping often removes 50-100 percent of the leaf-bearing crown robbing the tree of food-creating leaves.
Creation of weak shoots- As a defense mechanism, a tree will quickly grow (up to 20 feet in one year) food-producing shoots that are weak and prone to breaking, resulting in a more hazardous tree.
Added stress for the tree- If a tree does not have enough stored energy it will not be able to produce the chemicals required to defend the multiple wounds from a disease or insect attack.
"Sunburned" trees- The leaves within a tree's crown absorb sunlight. Without this protection, branches and trunks are exposed to high levels of light and heat which can burn the tissues beneath the bark.
Poor aesthetics- Topping removes the ends of branches often leaving unsightly stubs, and destroying the natural form of the tree. A tree that has been topped can never fully regain its natural form.
Higher maintenance costs- Trees that have been topped will need pruning more often, or may die and need to be removed. Topped trees are potential liabilities and can reduce property value.
Having trees topped may pose a high level of risk. Due to the fact that topping is considered an unacceptable pruning practice, damage caused by branch failure can be considered negligence in court.
By reducing branches properly, natural form can be preserved. The height or spread of a tree may need to be reduced in order to provide clearance for utility lines, for example. Several techniques can be used to accomplish this.
It is best to remove small branches back to the point of origin. In order to shorten a large limb, the branch should be pruned back to a lateral branch that assumes the terminal role (at least one-third the diameter of the limb being removed). It is possible to maintain the natural form of the tree using this method of branch reduction. In some cases, removing the tree and replacing it with a species that is more appropriate is the best solution.
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