The answer to whether a tree can survive without bark depends entirely on the degree and depth of the damage. Bark is the tree’s armor, forming a protective barrier against external threats like insects, animals, and weather. If only the outermost, dead layers are removed, the tree can often recover. However, damage that penetrates deeper into the inner, living tissues can quickly become a deadly threat. Understanding the precise layers of the bark and their functions is necessary to determine a tree’s prognosis after an injury.
The Essential Structure and Function of Bark
The bark is composed of several distinct layers that serve separate, yet interconnected, biological functions. The outermost layer is the cork, or outer bark, which is a protective layer of dead cells that insulates the tree from heat, cold, and physical damage. This layer can be removed without immediately harming the tree’s internal systems.
Just beneath the outer bark lies the inner bark, which is composed of the phloem tissue. The phloem is the vascular tissue responsible for transporting sugars, or food, produced during photosynthesis in the leaves down to the roots for storage and growth. This tissue is located just outside the vascular cambium and is extremely sensitive to damage.
The vascular cambium is a layer of actively dividing cells situated between the phloem and the wood (xylem). This layer produces new phloem cells toward the outside and new xylem cells toward the inside. Because the cambium is responsible for all new bark and wood production, its intactness is essential for a tree’s long-term health and structural integrity.
The Difference Between Superficial Damage and Girdling
Damage to the bark can be categorized into two major types, and the tree’s survival hinges on which layers are affected. Superficial damage involves the removal of only the dead outer bark, or perhaps a slight scrape into the phloem, but the wound does not extend completely around the circumference of the trunk. In these cases, the vascular cambium remains largely intact, allowing the tree to continue its normal transport of nutrients and water. The tree can then focus its energy on sealing the wound with new growth.
A destructive injury is known as girdling, which occurs when a continuous ring of bark is removed around the entire circumference of the trunk or a branch. Girdling must penetrate deeply enough to sever the phloem and the vascular cambium completely down to the wood (xylem) layer. This circumferential removal cuts the tree’s internal pipeline, preventing the downward movement of sugars from the leaves to the roots.
Even though the xylem—the woody tissue that transports water from the roots up to the leaves—remains intact, the tree cannot survive without the phloem. The roots are unable to receive the carbohydrates necessary to sustain life, leading to slow starvation of the root system. Once the roots die, they can no longer transport water or nutrients, and the tree eventually dies, even though the crown may look healthy for months or years after the damage occurs.
Factors Influencing Survival and Tree Recovery
If a tree has sustained bark damage that is less than a complete girdle, its ability to survive and recover depends on a variety of biological and environmental factors. The most important variables are the size and width of the wound relative to the trunk’s diameter, and the overall vigor of the tree. Generally, if the damage covers less than 25% of the tree’s circumference, the tree has a high probability of survival.
Trees do not “heal” in the way human skin regenerates; instead, they seal off the damaged area through a process called compartmentalization. The tree forms specialized tissue known as callus wood around the edges of the wound, which grows inward to cover the exposed wood and wall off decay. This process can be accelerated by ensuring the tree has adequate water and nutrients, which support the growth of the callus tissue.
The species of tree and the time of year the damage occurs also play a role. Some species are naturally better at compartmentalizing wounds than others. Wounds sustained during the active growing season, particularly early spring, may be easier to seal because the tree has the energy reserves to immediately begin forming callus tissue. Conversely, damage during dormancy may remain exposed longer, increasing the risk of infection by fungi or insects.