When a tree has its main branches or trunk drastically cut back to stubs, a process known as “topping,” the immediate answer is yes, it will grow back. However, the regrowth is structurally unsound, rapidly replaces the lost height, and is detrimental to the tree’s long-term health. Topping involves cutting large branches to points that lack a suitable side branch, creating large, open wounds. This process often results in a tree that is weaker, more susceptible to disease, and ultimately more hazardous.
Understanding Apical Dominance
The reason a tree responds to topping with explosive, seemingly chaotic growth is rooted in a natural biological process called apical dominance. This mechanism ensures that the central leader or main stem grows predominantly upward, establishing the tree’s overall vertical structure. Apical dominance is regulated by the plant hormone auxin, which is primarily produced in the terminal bud, the growing tip of the main shoot or branch.
Auxin travels downward through the tree’s vascular system, suppressing the growth of lateral buds further down the stem. This hormonal signaling directs the tree’s energy toward vertical growth, helping it compete for sunlight. When the terminal bud is removed by topping, the flow of auxin is interrupted, eliminating the suppression signal. This triggers the rapid activation of numerous dormant or adventitious buds, as the tree attempts to restore its lost canopy and photosynthetic capacity.
The New Growth: Water Sprouts and Structural Failure
The growth that emerges following the removal of apical dominance is characterized by numerous, fast-growing shoots known as epicormic sprouts, often called water sprouts or suckers. These shoots emerge rapidly in clusters near the large, exposed wounds left by the topping cuts. This rapid growth is a survival mechanism, but it does not produce the strong, integral branch structure of a healthy tree.
Unlike branches that develop naturally with a strong branch collar, water sprouts are weakly attached to the underlying wood. They arise from shallow, dormant buds and lack the necessary structural wood integration, making their attachment points fundamentally flawed. As these sprouts gain weight and length, their weak connection makes them highly prone to breaking off during high winds or heavy snow loads. Ironically, this structural failure increases the safety risk of the tree, which is often the opposite of the intended result of topping.
Long-Term Effects on Tree Health
The severe physical damage caused by topping extends far beyond the production of weak sprouts. The large cuts leave massive, open wounds that the tree cannot effectively seal, creating direct entry points for insects, fungi, and bacterial pathogens. Trees manage damage through compartmentalization (CODIT), but topping wounds are typically too large for the tree’s defense mechanisms to contain the decay. This often leads to extensive internal rot that weakens the branch and trunk structure.
The sudden removal of a large portion of the tree’s leaf mass severely stresses the organism because leaves are the tree’s food factory. This massive defoliation forces the tree to immediately expend huge reserves of stored energy to produce a replacement canopy. This stress compromises the tree’s ability to defend itself against pests and disease, leading to a long-term decline in vigor. Furthermore, stripping the canopy exposes the inner bark of the remaining limbs to intense sunlight, which can cause sunscald and cracking, creating additional points of entry for decay.
Recommended Pruning Techniques
Instead of topping, professional arborists use specific techniques to safely reduce a tree’s size while preserving its health and structure. The preferred method for reducing height or spread is the reduction cut. This cut involves shortening a branch by cutting it back to a smaller, healthy lateral branch.
The remaining lateral branch must be large enough to assume the terminal role and should be at least one-third the diameter of the branch being removed. This ensures the new growing point is structurally sound and prevents dieback of the remaining limb. Another technique is crown thinning, which involves the selective removal of entire branches back to the branch collar to improve air circulation and light penetration. Proper pruning adheres to the rule of never removing more than about one-third of the tree’s live crown in a single growing season to minimize stress.