Girdling is a technique used to kill a tree by completely removing a ring of bark from its circumference. This process severs the tree’s internal transportation system, which is necessary for survival. The time it takes for a girdled tree to die is not fixed, but depends on several biological and practical variables.
The Biological Mechanism of Girdling
A tree’s survival relies on two distinct vascular systems that run vertically through the trunk. The outermost system is the phloem, which is situated just beneath the bark and is responsible for moving sugars produced during photosynthesis from the leaves downward to the roots and other non-photosynthetic parts of the tree. The inner system is the xylem, which transports water and dissolved minerals upward from the roots to the crown.
Girdling works by severing the phloem layer all the way around the trunk. Once this layer is removed, the roots are immediately cut off from their source of energy, the sugars created in the leaves. The roots cannot access the necessary carbohydrates for metabolism and growth, leading to a slow starvation process. However, the xylem, which makes up the wood, remains temporarily intact, allowing water transport to the leaves to continue for a period. This means the crown may appear healthy and green for months or even a full growing season, masking the fact that the root system is dying.
Practical Girdling Techniques
Effective girdling requires completely severing the cambium layer, which is the thin, actively growing layer just inside the bark. This layer is responsible for producing both the phloem and xylem, and its removal prevents the tree from healing the wound. The cut must penetrate down to the sapwood, the outermost layer of the xylem.
If any strip of cambium is left intact, the tree can often “bridge” the wound by growing new vascular tissue across the gap. This bridging allows nutrient flow to resume and will delay or prevent death.
To ensure success and prevent this bridging, the removed ring of bark must be wide enough. For smaller trees, a width of one to two inches may be sufficient, but for larger, more vigorous trees, a strip between six and eight inches is recommended. Tools commonly used for this process include a hatchet to chop a continuous notch or a specialized girdling tool that cleanly strips the bark. Making two parallel cuts with a chainsaw and then removing the bark between them is another highly effective method to guarantee the cambium is fully removed across the entire circumference.
Key Variables Affecting the Death Timeline
The time it takes for a girdled tree to die can range from several months to multiple years, depending heavily on the specific circumstances. One of the largest influences is the species of tree, as softwoods, such as pines, generally succumb faster than dense hardwoods like oaks and maples. Hardwoods possess much larger stored carbohydrate reserves in their roots, allowing them to survive for longer periods after the phloem is severed.
The size and age of the tree also play a significant role in the timeline. Smaller, younger trees have fewer stored resources and a less extensive root system, meaning they may die within a single growing season. Conversely, a large, mature tree can rely on its extensive reserves for up to two or three years before the lack of energy fully kills the root system.
The completeness of the girdle is also paramount. A poorly executed cut that allows the tree to begin forming callus tissue will greatly extend the time to death.
Timing the girdling to coincide with the tree’s biological cycle can accelerate the process. Girdling performed in late spring or early summer is generally most effective because the tree has just expended a large portion of its stored energy for leaf-out and new growth. The tree is left at its most vulnerable point, as its root reserves are at their lowest just when the phloem is severed. Furthermore, applying an appropriate herbicide directly to the fresh cut surface can drastically reduce the timeline, often killing the tree in a matter of months rather than years.
Signs of Decline and Confirmation
The visible symptoms of decline often appear long after the girdling has been successfully executed. Because the xylem continues to supply water for a time, the initial signs of trouble are often subtle changes in the foliage.
Leaves may appear smaller than normal, exhibit premature autumn coloration, or develop a yellowing known as chlorosis, indicating nutrient stress. These symptoms occur because the roots are no longer able to sustain the canopy.
As the root system dies from starvation, the upper branches and twigs will begin to die back, typically starting at the top of the tree and progressing downward. Premature leaf drop is common, and the tree may attempt to produce a large final flush of seeds or fruit as a stress response, known as a distress crop.
The ultimate confirmation that the tree has died usually comes with the failure to leaf out in the subsequent spring. If the tree fails to produce any new green foliage or if a scratch test on the cambium reveals brown, dry tissue rather than moist, green material, the girdling process has been successful.