06/17/2026
ISA Arborist Exam Study Series – Part 1
⚠️ Caution: This topic may be controversial!
As I continue studying for the ISA Certified Arborist Exam, I plan to share interesting facts and concepts that I learn along the way. Today's topic is one that surprised me because it is such a common practice.
Topping Trees
When driving around, I see topped trees everywhere. Before taking classes through Penn State Extension, I never gave them much thought. During one of the courses, I learned why topping is considered one of the most harmful pruning practices for a tree.
Why Is Topping Harmful?
1. Loss of Food Production
When a large portion of the canopy is removed, the tree loses many of the leaves responsible for photosynthesis. Without those leaves, the tree's ability to produce food (carbohydrates) is greatly reduced.
2. Reduction of Auxin Production
Auxin is a hormone produced in the upper portions of the canopy. It travels downward through the tree and helps suppress dormant buds. When the canopy is removed, auxin production is reduced, allowing dormant buds to become active.
3. Emergency Growth Response
In response to the sudden loss of foliage, the tree uses stored energy reserves to rapidly produce epicormic shoots (often called water sprouts) in an attempt to rebuild its canopy.
Breaking It Down
🌳 Leaves are the tree's power plants. Without them, the tree cannot efficiently produce food.
🌳 Auxin helps keep dormant buds from sprouting. When auxin levels drop, those buds begin growing.
🌳 The tree is trying to survive. It quickly produces new shoots and leaves to replace what was lost.
Why Do People Top Trees?
Some common reasons include:
• Reducing the size of a tree
• Restoring or creating a view
• Attempting to make a tree safer
• Preventing interference with utility lines
• Maintaining a specific appearance
While these goals may seem reasonable, topping often creates long-term structural and health problems for the tree.
What are your thoughts on topping? Have you seen examples in your area?
Like, Follow, and Share for more interesting information as I continue studying for the ISA Certified Arborist Exam!
