Picture 1: The bark of a ponderosa pine tree grows into plates as the trunk grows taller and wider. Photo by Bob Dryja
Picture 2: Sections of older grey, lumpy textured bark on the left and right while layers of orange colored younger bark layers are in between. A drop of sap can be seen on the section of orange colored bark. Photo by Bob Dryja
By ROBERT DRYJA
Los Alamos
A ponderosa Pine Tree can immediately stand out due to its various kinds of dimensions. Some may reach 230 feet in height and be over 6 feet in diameter. They may live for up to 600 years but one tree has been found to be 935 years old. This means some trees were already 50 years old when Columbus discovered the Americas. It also means an occasional tree started growing in about the year 1100 in the Middle Ages. Size and age are remarkable.
The growth of bark reflects the growth of the trunk. A trunk diameter of 6 feet means a perimeter of about 18 feet. The bark surface that grows in the early years spreads out both upwards and around the trunk. The trunk becomes covered with what look like vertical plates. The relatively rigid bark comes apart as the perimeter of the trunk grows larger. (See Picture 1). Furrows develop between the plates as a result.
The furrows can provide a view of what is happening to bark as it becomes thicker as well as apart. Several things become apparent. First, the initial bark to grow on a young tree is textured with a lumpy surface that is dark grey in color. Second, bark grows in layers in later years underneath the initial bark. Third, some of the dark top layers of a plate may fall away, and younger orange-colored plates become visible below. Fourth, the furrows that develop between plates may penetrate the entire thickness of the bark. The bark of a ponderosa tree may become up to four inches in thickness and composed of many layers of bark, (See Picture 2).
A single layer is thin. It may be only 1/12 of an inch thick. A section of bark that is four inches thick therefore may be composed of about 50 layers. The smooth pieces of an orange-colored layer also are relatively small for their width and length. A piece may be only up to about three inches in size. Overall, the bark looks like pieces from some sort of jig saw puzzle, (See Pictures 3 and 4).
Water is transported up to the top of a tree from its roots to support the growth of its needles. Water also is transported down from the needles, taking nutrients to the roots. This flow is known as sap and the bark receives nutrition from it. The growing bark in turn can provide nutrition to beetles and other insects. A trunk may have numerous holes dug into by beetles probing for food.
A characteristic of bark is that it can be smelled. The sap can have an aroma that reminds people of vanilla. The aroma is produced as part of a category of chemicals called terpenes that can poison or discourage insects from infesting the tree. Holes that are bored into the bark by beetles can have sap enter holes to block beetles. Fissures also provide opening into the bark. Together they allow the chemicals to be released to the air and discourage insects from coming. The aroma also can attract birds that then eat insects on the tree. Bark therefore has a very dynamic life in the way it grows and protects a tree from insect infection.
Picture 3: Younger orange-colored bark is smooth next to the older, grey, lumpy textured bark. Photo by Bob Dryja
Picture 4: The smooth orange-colored bark grows like pieces of a jig saw puzzle. Photo by Bob Dryja