Trees with white bark are easily noticeable and striking. This distinctive feature often sparks curiosity about the specific species, contributing significantly to the visual appeal of many natural environments.
Iconic White Bark Trees
Among the most recognized trees with white bark are various species of birch and aspen. The Paper Birch (Betula papyrifera), also known as American white birch or canoe birch, is famous for its thin, white bark that peels in paper-like strips. This peeling often reveals a pinkish or salmon-colored inner bark, with older trees sometimes developing small black marks and scars. Young Paper Birches initially have reddish-brown bark, which transitions to white after three years. It is a fast-growing, yet short-lived, species, typically reaching heights up to 30 meters.
The European White Birch (Betula pendula), or Silver Birch, features white bark, though it may be less bright and often appears dirtier with grayish splotches compared to the Paper Birch. Its bark can peel in narrow strips, but generally, it peels less extensively than the Paper Birch. This species is native to Europe and Asia but is widely planted in North America as an ornamental tree.
Quaking Aspen (Populus tremuloides) is another widely distributed tree known for its smooth, chalky white bark. The bark of younger aspens is typically light green, becoming whiter with age. It often displays dark, diamond-shaped openings or prominent black knots and scars on its trunk. Quaking Aspens are characterized by their tall, slender trunks and their leaves, which “quake” or tremble in the slightest breeze due to flattened petioles.
Other Notable White Bark Trees
Beyond the birches and aspens, other tree species also exhibit white or very light-colored bark, each with unique characteristics. The American Sycamore (Platanus occidentalis) features exfoliating bark, peeling off in large, irregular, brittle sheets. This process reveals lighter, creamy, off-white, or greenish inner layers, creating a mottled, camouflage-like appearance. The lower portions of older sycamore trunks may retain rough, gray-brown bark, while the upper sections become increasingly white.
Certain Eucalyptus species, commonly known as gum trees, also have white bark. The Ghost Gum (Corymbia aparrerinja, formerly Eucalyptus papuana) is an example with smooth, sometimes powdery, white to cream-colored bark that sheds in thin patches. This Australian native can reach heights of up to 18 meters and is often found in open woodland areas. Other Eucalyptus species like Eucalyptus apodophylla (Whitebark) and Eucalyptus alba (White Gum) also possess smooth, powdery white or pinkish-white bark that contrasts with their often pendulous, bright green leaves.
Key Identification Clues
Identifying white bark trees involves observing several distinguishing features, including bark texture, leaf characteristics, growth habit, and geographical range.
Leaf characteristics provide further differentiation. Paper Birch leaves are triangular or egg-shaped with double-toothed edges, while European White Birch leaves are more pointed. Quaking Aspen leaves are nearly round with small, rounded teeth and long, flattened petioles that cause them to tremble. Eucalyptus species generally have lance-shaped or curved adult leaves.
Observing the overall growth habit, such as whether the tree is single-trunked or multi-stemmed, and its typical height and crown shape, can also aid in identification. Geographical range is another important factor; for instance, Paper Birch is native to northern North America, while Ghost Gum is found in Central Australia.
Why Bark Appears White
The white appearance of tree bark is due to specific biological and structural properties. In birches, the white color is attributed to a high concentration of betulin, a triterpene compound. Betulin occurs as crystalline deposits within the outer layers of the bark, reflecting most of the sun’s rays, similar to how snow appears white. This reflective quality helps protect the tree from sunscald and extreme temperature fluctuations, particularly in colder climates.
For trees like Quaking Aspens, the chalky white appearance is due to the constant sloughing off of outer cork cells, which are either entirely separate or in small clusters on the surface. This powdery layer contributes to the bark’s light color.
In sycamores and some eucalypts, the white coloration becomes apparent as older, darker outer bark layers shed, revealing lighter, newer bark underneath. The underlying chemical compounds in the newly exposed bark layers reflect light differently, contributing to the pale or white appearance.