Tree bark serves as a tree’s outer armor, safeguarding it from physical harm, pests, pathogens, and environmental stressors like extreme temperatures and water loss. While bark is a fundamental part of a tree’s biology, its shedding is a natural and expected process for many tree species, indicating growth and renewal rather than distress. Understanding this process helps to differentiate between a healthy tree’s natural cycle and signs of potential issues.
Key Reasons Trees Shed Bark
Trees shed their bark primarily to accommodate their increasing girth as they grow. As the tree’s trunk expands from the inside, the older, less flexible outer bark cannot stretch and must crack and slough off to make way for new layers forming underneath. This continuous outward pressure ensures the tree’s protective covering can keep pace with its expanding circumference.
Shedding also contributes to the tree’s ongoing protection and renewal. The process removes old, damaged, or dead outer bark, exposing fresh, healthy layers that maintain the tree’s defense system. This renewal fortifies the tree against environmental challenges and prevents moisture loss.
Bark shedding can also be a mechanism for trees to manage pests and diseases. By sloughing off outer layers, trees can rid themselves of harmful organisms like scale insects, fungi, mosses, or lichens that may have taken hold on the surface. This natural cleansing reduces potential threats to the tree’s health.
How Bark Sheds and Different Patterns
New bark originates from the vascular cambium, a thin layer of actively dividing cells located just beneath the inner bark. This cambium produces new wood (xylem) inwards and new inner bark (phloem) outwards. As new phloem cells are produced and pushed outward, they eventually become part of the outer bark, and older, outermost layers die and detach.
Trees exhibit various patterns as their bark sheds. Some species, like birch and sycamore, are known for their bark peeling off in long, thin strips or large, irregular sheets, revealing smoother, often lighter-colored bark beneath. Other trees, such as many pines or some maples, shed their bark in irregular plates or scales, a process referred to as flaking. Exfoliating bark, seen in crape myrtle, involves bark rolling or curling back to expose a different texture or color underneath.
Distinguishing Normal Bark Shedding from Distress
Normal bark shedding typically reveals healthy, often lighter-colored, intact bark underneath. This natural process usually occurs at specific times of the year or as the tree matures, and the shedding is generally uniform across the trunk or branches. If the tree otherwise appears robust with full, green leaves and no signs of insect damage or fungal growth, the shedding is likely part of its healthy growth.
However, certain signs indicate that bark shedding might signal distress. Shedding accompanied by sap oozing, discolored wood, or strong, unusual odors can be a cause for concern. Patches of bark falling off with underlying soft, mushy, or dark wood, or the presence of fungal mats, suggests disease or decay. Significant shedding outside the tree’s typical period or pattern, especially on young trees not known for shedding, warrants closer inspection. Other indicators of a problem include visible pests, extensive cankers (sunken, discolored lesions), or overall signs of tree decline such as wilting leaves, branch dieback, or stunted growth.