1. Starvation: Good pruning practices rarely remove more than one-fourth 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.
2. Shock: A tree's crown is like an umbrella that shields much of the tree from the direct rays of the sun. By suddenly removing this protection, the remaining bark tissue is so exposed that scalding may result. There may also be a dramatic effect on neighboring trees and shrubs. If the tree thrives in shade and the shade is removed, poor health or death may result.
3. Insects and Disease: The large stubs of a topped tree have a difficult time forming callus. The terminal location of these cuts, as well as their large diameter, prevent the tree's chemically based natural defense system from doing its job. The stubs are highly vulnerable to insect invasion and the spores of decay fungi. If decay is already present in the limb, the opening will speed the spread of the disease.
4. Weak Limbs: At best, the wood of a new limb that sprouts after a larger limb is truncated is more weakly attached than a limb that develops more normally. If rot exists or develops at the severed end of the limb, the weight of the sprout makes a bad situation even worse.
5. Rapid New Growth: The goal of topping is usually to control the height and spread of a tree. Actually, it has the opposite effect. The resulting sprouts (often called water-sprouts) are far more numerous than the 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.
6. Tree Death: Some older trees are more tolerant of topping than others. Beeches, for example, do not sprout rapidly after severe pruning, and the reduced foliage most surely will lead to death of the tree.
7. Ugliness: 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.
8. Cost: To an arborist with a saw, topping a tree is much easier than applying the skill and judgment of good pruning. Therefore, topping may cost less in the short run. However, the true costs of topping are hidden. These costs include reduced property value, the expense of removal and replacement if the tree dies, the loss of other trees and shrubs if they succumb to changed light conditions, the risk of liability from weakened branches, and increased future maintenance.
8 Reasons not to "top" your tree
Bend Tree Care - Tips and Information
"Trees have Dignity. Dignity means to command respect. Tree mutilation destroys a tree's dignity.
Plan before you plant."