The bark of any tree is more than just a good-looking façade. Even the most graceful aspen or stately ponderosa requires bark to protect its sensitive inner flesh from disease, parasites, and other environmental stresses, such as fire. Much like our skin, this outer layer is a necessity to protect the biological functions occurring within its protective covering.
However, there is no denying that in many cases, bark has certain characteristics that make it pleasant to behold or otherwise experience.
The bark of a ponderosa pine, for example, has large, deep furrows and grooves that divide the surface of the trunk into a series of scales that fit together like the pieces of an intricate natural jigsaw puzzle. And, although the bark of this particular tree is a very mundane shade of dark blackish-brown when young, as the tree ages, the bark becomes a shade of orange reminiscent of a Caribbean sunset, a somewhat extraordinary color to encounter in the Rocky Mountains.
Besides being lovely to behold, the bark of the ponderosa is also remarkable for its occasionally delectable scent. On warm days, a smell that has been likened to vanilla or butterscotch exudes from the cracks between slabs of bark on the tree, creating a unique type of Rocky Mountain aromatherapy.
The ponderosa pine reaches maturity at about 150 years old, and through its possible lifespan of 700 years or more, changes much in appearance. Younger ponderosas have a more typical “piney” shape, with pointed tops and live crowns that extend farther down the trunk. As the tree grows older, the crown becomes less pointy and flattens out on top, and the trunk self-prunes lower branches, making the Ponderosa more fire-resistant.
The bark of a ponderosa also changes considerably as the tree ages, losing its deep furrows and becoming more smooth and flaky. The color of the bark changes so dramatically that young trees and old trees are known colloquially by entirely different names, and were originally considered to be distinct species. The younger trees, with their deeply furrowed, dark bark are known as blackjacks or bull pines, while the older trees are called western yellow or western red pine, or ponderosa.
If you are out enjoying a hike on a glorious early spring day, and admiring the bark of ponderosa pines, you might begin to notice an interesting pattern. Many of the mature trees, which can be recognized by their orange puzzle-piece bark, are only this attention-grabbing color on one side. It is as though someone has gone through the forest with a paint brush, but done a shoddy job of touching up the trees. The other, “unpainted” side is a more typical gray bark color, though with the same physical characteristics as the more vivid part of the trunk.
The more you look around at the ponderosas in the forest, the more you might notice this peculiar pattern. All the pines in a group are orangey-red only on one side, and always on the same side as one another. As you become more and more curious about the reason behind this intriguing pattern, questions invariably arise. Could it be the result of a specific directional exposure leading to more light hitting one side of the tree? Or perhaps it has to do with wind, or some other environmental factor? Simple observation will probably not provide the answer, though many people hazard a guess that it has something to do with “sunlight.”
A report by the U.S. Forest Service shows that their guess is mostly correct. The change in the bark color of a ponderosa pine can be due in part to bleaching from the sun, which would explain why only the older trees are this color, and those only on one side. The report also pointed out that the bark varies in hue from place to place, sometimes a lighter grayish-yellow, and sometimes a more vibrant yellow-orange. There are almost certainly a great number of factors that determine the shade of the bark of a ponderosa pine, just as there are many things that determine the complexion of a person. Genetics, habitat, age; all play a part in creating a uniquely individual tree. It seems that trees, like most things in nature, are more complex than most people give them credit for, right down to their bark.
"Field Notes" is produced by the Montana Natural History Center.