Tree girdling occurs when a ring of bark is removed or damaged around the full circumference of a trunk or branch. This injury severs the phloem, the tissue beneath the bark that transports sugars from the leaves down to the roots. The roots, unable to receive energy, eventually starve and die. Although the xylem (which transports water up) remains intact for a time, a completely girdled tree will eventually perish. Immediate intervention is necessary to reconnect the transport system.
Assessing the Extent of Girdling Damage
Determining the severity of the wound is the first step, as it dictates the necessary repair technique. A tree is considered partially girdled if the damage covers less than 50% of the circumference; complete girdling involves 100% of the trunk. The depth of the injury is equally important, determining whether the cambium layer has been destroyed. The cambium is a thin layer of dividing cells that produces new wood and bark. If the cambium layer remains intact, the tree has a much better chance of recovery.
To check the depth, look for the greenish layer just under the outer bark. If this layer is gone and you see only the inner, lighter wood (xylem), the cambium is damaged. Signs of decline, such as a sparse canopy, wilting leaves, or premature autumn color changes, indicate that the damage is already impeding the flow of water and nutrients.
Simple Care for Minor and Partial Girdles
Wounds that do not completely circle the trunk or have only superficially damaged the outer bark can often be repaired without surgical grafting. The goal is to encourage the tree to naturally form new tissue, a process called callousing, to cover the exposed wood. Begin by carefully removing any loose, jagged, or torn bark edges from the wound using a sharp, clean knife. Shape the wound into a smooth, vertical oval or football shape, known as bark tracing. This shape encourages faster wound closure from the sides.
The smooth edges allow the callousing tissue to grow over the exposed wood more efficiently. Avoid applying commercial wound dressings or sealants, as these can trap moisture and pathogens, hindering the tree’s natural healing process. Following the tracing, reduce stress on the tree by ensuring it receives consistent water, especially during dry periods.
Bridge Grafting for Complete Girdles
When a tree is completely girdled, the only viable option for repair is bridge grafting, a procedure that physically reconnects the vascular system. This technique requires dormant scion wood, which are one-year-old, straight shoots from the same species of tree. Scions must be collected while the tree is leafless. The procedure should be performed in early spring, just as the buds begin to swell, because the cambium is most active then. This timing increases the chances of the graft taking hold.
First, clean the damaged area and remove any loose bark. Gather enough scion wood to place a bridge every two to four inches around the circumference of the trunk. Each scion should be three to four inches longer than the width of the wound and sharpened into a wedge shape at both ends. Next, cut small, inverted T-shaped flaps into the healthy bark both above and below the girdled section. Ensure the cuts reach the live cambium layer.
The wedge-shaped ends of the scions are gently tucked under these bark flaps. Ensure the outer layer of the scion aligns perfectly with the inner bark of the trunk. The scions must be oriented with the buds pointing toward the top of the tree to ensure correct phloem and xylem flow. Secure the scions in place with small brad nails or grafting tacks. Finally, seal all connections and the exposed wood with a specialized grafting wax or compound to prevent desiccation and protect the graft union.
Long-Term Monitoring and Support
After the immediate repair, the tree requires sustained care to maximize the chance of survival and recovery. The primary focus is on stress reduction, meaning providing adequate moisture without over-saturating the soil. Deep watering during periods of drought is important to support the canopy. Avoid applying fertilizer for the first year, as this can force energy into new leaves instead of wound healing.
Regularly monitor the repair site, checking the scions for signs of successful attachment, such as swelling or the formation of callus tissue. If bark tracing was performed, look for the edges of the bark to roll inward, gradually closing the exposed area. Even with a successful bridge graft, the tree will have a structural weakness and may never fully regain its original vigor or height. Ongoing structural monitoring is often necessary, and installing protective tree guards can prevent future damage from rodents or machinery.