Peeling bark (exfoliation) is a distinct visual characteristic that serves as a primary identifying feature for many tree species. This process is a natural and healthy part of a tree’s growth cycle. For these specific trees, the shedding of the outer layer is not a sign of distress but rather a genetically programmed phenomenon. The texture, color, and pattern of this sloughing bark offer unique ornamental interest, transforming the trunk into a dynamic feature in the landscape.
The Biology Behind Exfoliating Bark
The shedding of a tree’s outer layer of bark is a necessary physiological adaptation driven by two main factors: physical expansion and biological defense. Trees grow radially from the inside out, meaning the trunk’s diameter continuously increases throughout its life. Because the outer bark, or periderm, is composed of rigid, dead cork cells, it cannot stretch to accommodate this outward pressure. This pressure causes the inelastic outer layer to crack and split, leading to its eventual detachment, allowing the new, larger layer of bark underneath to form a fresh protective covering.
The second function of this regular shedding is to maintain a sterile and clean surface. By continually sloughing off the oldest outer layers, the tree effectively removes biological “hitchhikers” that may have established a hold on the trunk, helping prevent the buildup of mosses, lichens, fungi, and insect pests.
Trees Known for Horizontal and Sheet Peeling
Some of the most recognizable examples of exfoliating trees shed their bark in thin, paper-like sheets or horizontal strips. The birches (Betula species) are the most famous, with the Paper Birch (Betula papyrifera) known for its smooth, bright white bark that peels away in large, papery horizontal curls, exposing a pinkish or cream-colored inner layer. The River Birch (Betula nigra) has a finer texture, with the outer layers peeling back in thin, ragged, cream-to-cinnamon-brown sheets. Another species is the Paperbark Maple (Acer griseum), a smaller tree with coppery-cinnamon bark. Its bark exfoliates in fine, translucent, paper-thin curls that often remain partially attached, giving the trunk a textured, metallic appearance.
Trees Known for Vertical and Platy Peeling
In contrast to the fine, horizontal sheets of the birches, other species shed their bark in thick, vertical strips or large, irregular plates. The Shagbark Hickory (Carya ovata) epitomizes this pattern, with its thick, gray bark separating into long, curved plates attached only near the center, giving the trunk a rugged, shaggy texture. The American Sycamore (Platanus occidentalis) and the London Plane tree exhibit a platy exfoliation that results in a mottled, camouflage-like pattern. The dark outer bark flakes off in large patches, revealing a smooth, lighter-colored inner bark that ranges from cream and white to pale green and gray. Crape Myrtles (Lagerstroemia indica) also shed their bark in irregular patches, exposing a smooth, polished underlayer that is often a mix of light tan and cinnamon.
Distinguishing Healthy Peeling from Tree Distress
It is common for observers to confuse natural bark exfoliation with a sign of a sick or damaged tree. The most reliable indicator of healthy peeling is the appearance of the tissue underneath; natural shedding exposes healthy, fresh, and often brightly colored bark. This process is uniform across the trunk and is characteristic of the species throughout its life. Peeling that indicates distress is usually localized and accompanied by other warning signs. If the peeling exposes entirely bare wood, or if the underlying tissue is discolored, soft, or covered in dark fungal growth, the tree may be struggling with disease or pests.