When the main trunk or all of the ends of branches on a tree are cut straight off the top of a tree, that is called tree topping. While people sometimes do this to reduce the overall height of a tree, the practice of tree topping is never recommended. Industry standards for pruning unanimously agree this practice is harmful and specifically prohibit topping.
There are a number of ways topping harms trees. First, topping promotes decay, creating wounds that serve as an entry point for insects and disease. It also produces rapid growth of “watersprouts.” The waterspouts and smaller remaining limbs are structurally insecure and greatly increase the likelihood of limb breakage and tree failure. Finally, because topping removes a large portion of the tree’s leaves. This decreases the tree's ability to produce energy (photosynthesis), weakening its vigor and starving the tree.
The best method to avoid topping is to select the right tree in the first place, always considering the full grown size and height of the species. Proper pruning from a young age will also encourage a strong form for the life of the tree. As the tree matures, reduction pruning can help provide clearance from nearby structures while reducing the risk of tree failure.
View more tips