Tree bark is the complex outer layer that acts as a protective shield, defending the inner, living tissues from environmental threats, pests, and physical injury. Beneath the rough outer bark lies the phloem, which transports sugars and nutrients produced by the leaves throughout the tree. Loss of this exterior covering directly impacts the tree’s ability to regulate temperature, manage moisture, and transport energy. Determining whether peeling is a harmless, natural process or a symptom of serious distress requires careful observation of the pattern and the material revealed underneath.
Healthy Shedding and Normal Exfoliation
In many tree species, bark shedding is a normal part of growth and maturation. As a tree increases in girth, the rigid outer bark cannot expand and is naturally pushed outward and sloughed off. This process is a sign of a healthy, actively growing specimen.
For species known for exfoliating bark, the peeling is usually uniform and reveals a fresh, healthy layer beneath that is often lighter or differently colored. For instance, shagbark hickory is characterized by long, thick strips that curl away from the trunk. River birch features thin, papery sheets that flake off, while some maples display a cinnamon-colored new bark after the outer layer peels.
Damage from Temperature and Physical Injury
Abiotic factors, such as extreme weather and accidental wounds, frequently cause bark to crack and peel in localized areas.
Sun Scald and Frost Cracks
One common weather-related issue is sun scald, often called southwest winter injury. This occurs when intense winter sunlight heats the bark on the south or southwest side of the trunk, activating the underlying cambium cells. When temperatures rapidly drop at night, the activated tissue freezes and dies, resulting in vertical cracks and eventual bark detachment.
Temperature fluctuations can also cause frost cracks, which are deep, vertical splits resulting from the trunk rapidly expanding and contracting due to temperature extremes. The bark surrounding these splits may peel away as the tree attempts to form a callus layer to compartmentalize the wound.
Mechanical Injury
Physical or mechanical injury is another cause of localized bark peeling, typically occurring near the base of the trunk. Damage from lawnmowers, string trimmers, or construction equipment disrupts the bark and the phloem layer beneath it.
The peeling is concentrated around the perimeter of the wound as the tree attempts to seal off the damaged section with new growth. Although this peeling is a response to injury, the open wound creates an entry point for pathogens.
Identifying Pests and Pathogen Attacks
When peeling is accompanied by discoloration, holes, or abnormal growths, it signals an active attack by insects or pathogens.
Cankers and Fungal Infections
Fungal and bacterial infections often manifest as cankers, which are localized, sunken, or discolored lesions on the bark. These infections kill the tissue between the bark and the wood, causing the dead bark to crack and peel away, often revealing dark tissue beneath.
If a canker encircles the trunk (girdling), it cuts off the transport of sugars, leading to the death of the tree above that point.
Insect Borers
Insect borers are a significant biological threat that causes bark to detach as they feed just beneath the surface. The larvae tunnel through the phloem and cambium layers, disrupting the flow of water and nutrients, which results in large patches of dead, loose bark.
Signs of a borer infestation include small, round or D-shaped exit holes, or the presence of frass. Frass is a sawdust-like excrement pushed out of their tunnels that often collects at the base of the tree.
Internal Decay
Extensive internal wood decay, often caused by root rot or fungal infections, can also lead to bark peeling, particularly near the base. This peeling is usually associated with wood that feels soft or spongy when probed, indicating significant internal deterioration. The presence of mushrooms or other fungal fruiting bodies directly on the trunk or near the base indicates advanced internal decay.
Determining the Severity and Next Steps
The severity of bark peeling relates directly to the amount of living tissue damaged and the total circumference affected. If the peeling exposes healthy, green inner tissue that is actively trying to heal, the damage is likely superficial or a manageable localized wound. If the peeling exposes dry, brown, or soft wood, it indicates that the cambium layer, which produces new wood and bark, has been killed.
A tree faces a severe threat if bark loss extends more than 50% around the trunk’s circumference. This level of girdling severely compromises the tree’s vascular system.
For localized injuries, preventative measures can limit future damage. These include applying mulch away from the trunk to avoid mechanical injury, and protecting young trees susceptible to sun scald with commercial tree wraps or light-colored paint.
If the peeling is widespread, accompanied by active insect infestation, or shows signs of significant fungal growth, consult a certified arborist. An arborist can accurately diagnose the cause, assess the extent of internal damage, and recommend appropriate treatment to either save the tree or safely remove it if the structural integrity is compromised. Early intervention is often the best defense against issues that can quickly lead to tree decline or structural failure.