The protective covering of a tree, known as bark, is a complex layer of dead and living tissues that shield the inner wood from physical damage, insects, and disease. When people see patches of bark peeling from their maple trees, they often worry the tree is dying. While excessive or rapid shedding can signal a serious underlying problem, minor peeling is often a healthy, natural part of the tree’s growth. The difference lies in understanding the appearance of healthy bark versus the signs of damage or distress.
How to Identify Healthy Maple Bark
A maple tree’s bark appearance changes dramatically as it matures, making age an important factor in determining what is normal. Young maple trees, regardless of species, typically have smooth, thin, and light-gray bark. This smooth texture allows the tree to expand easily in its early, rapid growth years. As the tree ages, its bark thickens and develops distinct patterns, which vary among different maple types. Sugar maples (Acer saccharum) develop deep, vertical furrows and ridges. In contrast, the bark of a mature silver maple (Acer saccharinum) is often visibly shaggy, peeling away in long, thin strips. The presence of these characteristic fissures and plates on older trees is a sign of normal development.
Natural Causes of Bark Peeling
The primary reason healthy maple trees shed their outer layer is due to secondary growth, which increases the tree’s girth. The living cambium layer, located just beneath the bark, constantly causes the tree trunk to expand in diameter. This continuous expansion pushes the older, outermost bark layers outward. The outermost layer of bark, known as the rhytidome, is composed of dead, corky cells that are inelastic and cannot stretch with the growing trunk. As the circumference increases, the rigid outer bark is forced to crack, split, and eventually exfoliate in small pieces or flakes. This is a slow, gradual process and the peeling is generally uniform around the trunk, revealing a healthy, fresh layer of bark underneath.
Serious Issues Indicated by Shedding Bark
While minor flaking is natural, the rapid loss of large plates or strips of bark often signals a serious issue stemming from environmental stress, pests, or disease. This pathological peeling is distinct because it indicates that the underlying tissue is compromised. To differentiate, look for large areas of exposed, bare wood, oozing sap, or soft, discolored patches, as these signs indicate significant stress.
Sunscald
Sunscald is damage caused by sudden temperature fluctuations in winter. The sun warms the south or southwest side of the trunk on a cold day, stimulating cellular activity. A rapid drop in temperature at night then freezes and kills the living cells. This causes the bark to die and peel off, often the following summer.
Pests and Borers
Insects that bore beneath the bark are a major cause of pathological peeling, as they disrupt the tree’s vascular system. Specific pests, such as various borer species, tunnel into the tissues under the bark, which kills the overlying layer. This damage causes the bark to detach in large, premature patches, and the area may show signs of sawdust-like frass or small, circular exit holes.
Fungal Infections
Fungal infections can also lead to bark death and sloughing, often appearing as distinct, localized lesions called cankers. Fungi kill the bark in specific spots, which then dries out, cracks, and falls away. This process reveals discolored wood underneath.