Yes, sycamore trees shed their bark in a process known as exfoliation, a defining characteristic of the species. This phenomenon is a normal part of the tree’s growth cycle and is not a sign of sickness or distress. The American sycamore, Platanus occidentalis, is famous for this distinctive appearance. This natural habit results from a mismatch between the tree’s rapid growth and the physical properties of its outer skin.
The Biological Reason for Bark Exfoliation
The sycamore’s shedding habit lies in the unique combination of its rapid secondary growth and the rigidity of its outer bark tissue. Sycamores are known for their fast growth rate, especially when young and in ideal, moist riparian environments. As the trunk rapidly increases in diameter each year, the outer protective layer, called the rhytidome, is unable to stretch to accommodate the expansion.
Most trees possess elastic bark that can stretch or develop deep fissures to manage increasing girth. The sycamore, however, develops less flexible bark that resists this outward pressure from the interior woody tissue. Consequently, the stiff outer layers cannot remain intact as the tree’s circumference expands.
This internal pressure causes the older, rigid bark to crack and break away in large, irregular plates or patches. The exfoliation process exposes the living inner bark layers, which are not yet fully rigid and have a different coloration. This natural shedding can occur throughout the year, becoming more pronounced during periods of rapid growth, such as the warmer summer months.
Understanding the Unique Patchy Appearance
The result of this constant exfoliation is the sycamore’s camouflage-like pattern, a visual consequence of the exposed underlayers. The outer, older bark that is shed is typically rough, dark gray or brown. When these rigid patches flake off, they reveal the smoother, vibrant tissue beneath.
The newly exposed inner bark presents a remarkable contrast, displaying colors that range from creamy white and pale tan to a light olive green. These distinct color patches represent different ages of bark exposure, with the whitest areas being the most recently uncovered. As these lighter patches are exposed to air and weather, they gradually darken before eventually hardening and exfoliating.
This mottled pattern, particularly noticeable on the upper limbs and younger trunks, gives the sycamore a ghostly appearance, especially in winter.
Distinguishing Normal Shedding from Health Issues
For the sycamore, peeling bark is overwhelmingly an indicator of normal growth, but it is important to recognize the difference between natural exfoliation and signs of actual distress. Normal shedding involves the flaking of dry, rigid patches that fall away cleanly, primarily from the younger parts of the trunk and the branches. The exposed area beneath should appear firm, smooth, and healthy, with the characteristic light coloration.
A cause for concern arises when the bark loss is sudden, extensive, and occurs primarily on the lower trunk of a mature tree, which typically retains a more furrowed, darker bark. Signs of an underlying health problem often include localized areas of bark death accompanied by weeping sap or a foamy, watery discharge known as slime flux or wetwood. This oozing fluid is often dark and may stain the bark below the lesion.
Another indicator of an issue is the presence of long, vertical strips of bark suddenly peeling away, which is unlike the typical irregular flaking. Additionally, if the exposed wood beneath the bark shows signs of powdery mildew, fungal growth, or insect activity, a professional arborist should be consulted. The bark itself should not exhibit signs of decay or localized necrosis due to this natural shedding process.