Tree Anatomy: Bark

Now that the leaves have fallen from deciduous trees, this is a great time to admire an often-overlooked part of tree anatomy: the bark.

Bark Function

Bark serves several crucial functions for the tree. Inner bark transports nutrients throughout the tree. Unintentional girdling of a tree with staking materials or ropes causes severe damage to the tree by preventing this distribution of nutrients. The outer bark forms a protective layer made of dead cells. New cork layers form and die and the bark grows thicker. Waste products are deposited in this outer bark. A tree’s bark will peel away in long strips or flake away in small scales depending on the orientation of this cork layer to the outside of the tree. The bark of the Western red cedar sheds in long thin strips, as seen in the picture above. The outer bark protects the tree from the elements, the sun’s rays, fire, animals and insects.

Bark Patterns

There is an astounding variety of bark patterns from the square bark division of the Oregon white oak, to the elongated asymmetrical plates of the Ponderosa pine, to the thick rivulets of bark of the Douglas fir (seen above left to right). The variety of bark pattern is not only determined by the species of tree, but also by the age of the tree. Many species exhibit smooth bark at a young age and develop rougher bark later in life. The subtle bark pattern difference of two distant trees is sometimes not obvious. Lightly rubbing the side of a crayon over a piece of paper laid on the bark will reveal the characteristic patterns. The bark rubbings can then be compared side by side without the visual distraction of color variations.

Visible Bark Features

Trees exchange gases with the atmosphere through pores in the outer bark called lenticels. In some species, these lenticels are visible from the outside of the bark and are used in tree identification. The lenticels are a prominent feature of the bark of the flowering cherry tree seen below.

Many trees and shrubs are selected for planting in our landscapes due mainly to the visual interest of the bark. Along with winter berries, colored bark lends visual interest to the winter landscape. The coral bark Japanese maple branch seen below has multicolored bark with white and yellow at the base of the main trunk, green at the branch bases reddening to crimson twig tips.

On your next winter stroll, note the unique features of the barks of the trees in your neighborhood. You might be surprised at the diversity of patterns you have overlooked in the past.