Tree girdling is a deliberate method of tree removal involving cutting away a band of bark and the underlying growth tissue around the circumference of a trunk. This technique is often employed for selective tree clearing where immediate felling or the use of herbicides is undesirable.
The goal is to induce tree death by interrupting the biological systems that sustain life, allowing the tree to die slowly while standing. For this method to be successful, a specific amount and depth of tissue must be removed to ensure the tree cannot repair the damage.
The Vital Role of the Bark Layers
A tree’s survival depends on a thin layer of living tissue just beneath the rough outer bark. The outer bark primarily protects the tree against weather, insects, and physical damage. Directly beneath this protective shield lies the phloem, which transports sugars produced during photosynthesis from the leaves down to the roots. These sugars are the energy source that keeps the root system alive.
Inside the phloem is the vascular cambium, a single layer of dividing cells that generates new phloem toward the outside and new wood (xylem) toward the inside. The cambium is the growth engine that increases the tree’s girth. Girdling works by completely severing the phloem layer, stopping the downward flow of nutrients to the roots.
Once the phloem is interrupted around the entire trunk, the roots are starved of energy, eventually leading to their death. The rest of the tree above the girdle remains alive for a time using stored reserves, but the entire organism will eventually perish without new energy from the leaves. The xylem, which transports water and minerals up from the roots, remains functional, so the canopy may appear healthy for several months or even a year after the girdle is established.
The Critical Dimensions for Effective Girdling
To ensure a tree dies from girdling, two dimensions must be addressed: the width and the depth of the cut. The removal must be complete around the entire trunk, creating a 360-degree gap. Leaving even a small strip of intact tissue allows the phloem to transport enough nutrients to sustain the roots, enabling the tree to survive and attempt to bridge the gap.
The width of the removed band must be wide enough to prevent the tree from bridging the wound before it starves. For most trees, a removal band between 4 and 8 inches wide is recommended. A narrow cut, such as one or two inches, can often be healed by the tree’s natural growth mechanisms, especially on younger specimens. The wider band forces the tree to expend more energy attempting to close the wound, draining its reserves quickly.
The depth of the cut is the most critical factor. Removal must penetrate through the outer bark and the phloem, extending down to and including the cambium layer. If the cambium is not fully removed, the cells will continue to divide and rapidly produce new phloem and xylem, healing the wound. A successful girdle exposes the underlying sapwood, or xylem, which is the hard, pale wood of the trunk.
To confirm the cambium is fully removed, the exposed wood should be scraped to ensure no slick, greenish-white tissue remains. The cambium is a very thin layer that is easily missed, but its complete removal is necessary for successful girdling.
Variables Influencing Girdling Success
The success and speed of tree death after girdling are influenced by several biological and environmental factors. The species of tree plays a significant role, as some possess a greater capacity for sprouting and healing than others. Certain oaks, maples, and black locusts are known for their aggressive ability to send up new shoots from the root collar or the trunk below the girdle, which can quickly re-establish nutrient flow to the roots.
Girdling is most effective when performed in the late spring or early summer, a period when the tree is actively growing and the sap is flowing. During this time, the tree has depleted stored carbohydrates to fuel new growth, making it vulnerable to the interruption of the phloem. When the cambium is active, the bark is also easier to peel away cleanly, helping ensure the entire layer is removed.
The age and vigor of the tree also modify the outcome. Younger trees, which are actively growing and possess a higher ratio of sapwood to heartwood, often have more extensive energy reserves and a greater ability to initiate a repair response. These younger specimens can attempt to bridge the girdle more quickly or produce vigorous basal sprouts. Conversely, older, less vigorous trees with limited energy reserves succumb to the damage more quickly after proper girdling is performed.