Ring barking, technically known as girdling, involves the complete removal of a strip of bark around a tree’s trunk. This injury severs the tree’s internal transportation system, an act that is almost universally fatal. The timeline for death is highly variable, ranging from a single season to several years. Mortality depends on understanding the biological mechanisms destroyed and the factors that influence the tree’s internal reserves.
The Biological Mechanism of Girdling
A tree relies on two distinct vascular tissues for survival: the xylem and the phloem. The xylem, located deeper inside the trunk, transports water and dissolved minerals upward from the roots to the leaves. The phloem, which lies in the inner layer of the bark, is responsible for moving sugars produced during photosynthesis downward to the trunk and the root system.
Girdling kills the tree by interrupting the downward flow of sugars through the phloem. The leaves and canopy remain alive initially because the deeper xylem tissue remains intact, allowing water to move upward. However, the roots are cut off from their energy source, forcing them to rely on stored carbohydrates. This root system starvation leads to a delayed decline rather than an immediate collapse.
Factors Influencing the Mortality Timeline
The time it takes for a ring-barked tree to die varies significantly, often spanning from a few months to four years or more. The tree’s species plays a large role; some conifers, such as Larix and Pinus species, have been observed to survive for up to five years after being girdled. In contrast, some hardwoods may succumb faster, with most northern hardwoods dying within four years, and some within one year.
The season in which the damage occurs also affects the speed of mortality. Girdling performed in late spring or early summer, when the tree is actively growing and roots demand the most sugars, typically results in the quickest death. Conversely, damage inflicted during the dormant winter season is often less effective, as the roots are not actively drawing on reserves and may encourage vigorous sprouting in the following spring.
The width of the removed ring is also a factor, as a wider girdle prevents the tree from bridging the wound with new tissue. Younger trees tend to die faster because they have smaller carbohydrate reserves in their roots compared to large, mature trees, which can survive on stored energy for several years. Species with ring-porous wood structures may be more quickly top-killed than those with diffuse-porous wood.
Observable Signs of Tree Decline
The visual symptoms of decline often do not appear immediately following girdling, but become noticeable in the growing season after the damage occurred. The first signs are typically visible in the canopy, as the starved root system can no longer sustain the entire tree. These symptoms include leaves that are smaller than normal, appearing stunted or sparse, and often exhibiting a pale, yellowish color.
The tree may show signs of distress through its annual cycle, such as premature fall coloration and early leaf drop. As the roots continue to die, the decline progresses from the top down, leading to dieback of twigs and branches in the upper canopy. Ultimately, the entire crown will thin out, and the tree will fail to leaf out completely in a subsequent spring, confirming its death.
Mitigation and Salvage Options
If a tree has been completely girdled, the chances of survival are low, but immediate intervention can be attempted through bridge grafting. This process involves using small branches, called scions, taken from the same tree to create a bridge connecting the living bark tissue above and below the damaged area. The scions are grafted into the trunk to restore the flow of sugars and nutrients down to the roots.
This salvage procedure must be performed as soon as possible after the damage, ideally when the tree’s sap is running actively in the early spring, to maximize the chance of a successful union. For very young trees, a more drastic option involves cutting the trunk below the girdle and training a vigorous shoot to become the new leader. If a mature tree shows significant signs of terminal decline despite repair attempts, it becomes a safety concern. Dead wood is brittle and prone to sudden failure, requiring professional removal to prevent hazards to surrounding property and people.