The Threats to Trees
Humans can threaten a tree's health at three levels.
- The roots: soil compaction, construction activities, and pollution (oil, herbicides, and toxic chemicals) can injure or kill roots, and weaken or kill the tree.
- The trunk: damage to the bark wounds the tree, and some of the energy needed for maintenance and growth of the tree's existing root and branch system is redirected to healing the wound instead.
- The crown: improper pruning and air pollution can result in a decline in food production in the leaves, and the entire tree suffers.
See the city's Tree Management Ordinance or contact City Horticulturist Cynthia Holloway at 615-895-8059 for more information or questions.
Effects of Topping
The most obvious way that trees are injured is by topping. Tree topping is the drastic removal of large branches that are cut back to stubs. Topping is an unacceptable practice, although many people are unaware of its detrimental effects. As a result, the homeowner may spend hundreds of dollars to perform this senseless act, often with the best of intentions.
We'd like to share with you information about the consequences of topping and about the better alternatives that are available.
Good pruning practices rarely remove more than 1/4 to 1/3 of the crown, which in turn does not seriously interfere with the ability of a tree's leafy crown to manufacture food. Topping removes so much of the crown that it upsets an older tree's well-developed crown-to-root ratio and temporarily cuts off its food-making ability.
A tree's crown is like an umbrella that shields much of the tree from the direct sun. By suddenly removing this protection, the remaining bark tissue is so exposed that sun scalding may result.
Insects and Disease
The large stubs of a topped tree have a difficult time forming callous. The stubs are highly vulnerable to insect invasion and the spores of decay fungi. If decay is already present in the limb, opening the limb will speed the spread of the disease.
At best, the wood of a new limb that sprouts after a larger limb is cut is more weakly attached than a limb that develops normally. If rot exists or develops at the severed end of the limb, the weight of the sprout makes a bad situation even worse. These limbs are much more likely to break and fall during a storm.
Rapid New Growth
The goal of topping is usually to control the height and spread of a tree. Actually, it has just the opposite effect. The resulting sprouts (often called water sprouts) are far more numerous than normal new growth and they elongate so rapidly that the tree returns to its original height in a very short time - and with a far denser crown.
Some older trees are more tolerant to topping than others. Trees that do not sprout readily after severe pruning have reduced foliage, therefore less food is manufactured and most of the time this leads to the direct death of the tree.
A topped tree is a disfigured tree. Even with its regrowth it never regains the grace and character of its species. The landscape and the community are robbed of a valuable asset.
To a worker with a saw, topping a tree is much easier than applying the skill and judgment of good pruning. Topping may cost less in the short run. However, the true costs of topping are hidden. These include:
- Expense of removal and replacement if the tree dies
- Increased future maintenance
- Reduced property value
- Risk of damage from the weakened branches