CORVALLIS, Ore. – This fall’s display of colorful leaves has blown to the winter winds and now garden trees are beginning to reveal their subtle beauty with the colors and textures of their bark.
Neil Bell, an Oregon State University Extension community horticulturist, explains how the function of bark leads to such variety in its appearance. “The basic function of bark is to help the plant survive drying winds and extremes of temperature," he said.
The cork-like protective layer is dotted by pores that permit plant tissues to breathe. The size and pattern of pores is characteristic of certain kinds of trees. Some trees, such as paper birch, have smooth bark. These form new paper-thin layers of tissue every year. As the tree grows, the pores stretch, forming horizontal stripes in the bark. Smooth-barked aspens produce new layers of inner bark while outer layers are shed as powdery cells.
Smooth bark sheds water easily, keeping the trunks dry and less susceptible to lightening strikes. But smooth-bark trees are more vulnerable to chewing rodents and less resistant to fire than trees with thicker bark.
Trees with scaled or furrowed bark produce new bark tissue in overlapping patches. Older tissue is pushed outward, forming a thick coat of non-living cells. In some trees, this old coat stretches as the tree grows, splitting the bark into furrows. In others, including eucalyptus and plane trees, older bark sloughs off in patches, revealing an eye-catching pattern of different colors.
Shaggy-barked plants, such as grapes and cedars, form new bark tissues alternated with layers of food-conducting tissues. As the plant grows the layers separate, splitting the bark vertically into a shaggy coat.
"Take time to notice the tones and textures of the winter garden," Bell said. "Colorful branches, such as those of the red- or yellow-twig dogwood, also add to the subtle beauty of the leafless season."
To help select plants that will catch your eye in winter, the OSU Extension Service offers the publication, “Plant Materials for Landscaping: A List of Plants for the Pacific Northwest,” PNW 500. Order online, or call 800-561-6719 to purchase a copy. Cost is $2.50 plus shipping and handling.