Bark is so common that we scarcely take the time to appreciate its wonders. It is of course essential to trees and vines—and very useful to humans in many ways—but it also intrigues at least two photographers, at different ends of the earth, who have contributed text and images. We have each spent much time enjoying the presence of bark, and we hope to entice other photographers to share the experience.
Bark surrounds every tree. It is the “ruptured epidermis” of a tree (Raven), the cracked and furrowed skin that protects—and beautifies—a tree’s trunk and roots after a certain age. There are many different ways to look at bark: one is motivated by the botanist’s interest in the origin, composition and function of bark; another is the field naturalist’s desire to identify species; a third is driven by the incessant human urge to make use of natural “resources;” and a fourth, the photographer’s gaze, is fixated on the visual appearance. In this post I’ll naturally focus on the various looks of bark, after some brief words about botanical interest and practical benefits, and then turn the podium over to Pete.
“Bark” is a colloquial term, not a technical botanical one. Bark is not a natural kind like “species,” but a widespread feature of many vascular plants, and so there is no unified account or evolutionary history of all its varieties—it varies with its species. Perhaps that’s why there is no good general interest book on bark. But I did consult the introduction to Gil Nelson, Christopher J. Earle, and Richard Spellenberg, Trees of Eastern North America (Princeton U.P., 2014); Peter H. Raven, Ray F. Evert, and Susan E. Eichhorn, Biology of Plants, 7e (W. H. Freeman, 2005); and of course the ubiquitous Wikepedia.
Bark includes all the tissues outside the vascular cambium, the growing edge of the woody part of trees, shrubs and vines; this cambium produces xylem to the inside and phloem to the outside. Xylem and phloem are terms we all learned in high school biology and still constantly confuse, like stalactites and stalagmites. Xylem (from the Greek xylon, meaning “wood”) are vessels that conduct water and nutrients upward from the roots to the leaves; phloem (from the Greek phloios, “bark”) are vessels that transport nutrients down from leaves to roots—a marvelously efficient circuit (though it is more complicated than that). Just outside a tree’s wood lies the inner bark or cork cambium; it is living tissue, and produces the outer bark, or cork, which is the dead tissue that we see. As the tree grows in girth, the cork is no longer able to keep abreast, and so it deforms—it wrinkles, cracks, splits and furrows—creating a surface unique to every individual tree, though quite similar to other trees of its species. Internal to the cork region, there are surprisingly many parts and structures, all of which delight botanists and bedevil students. I’ll spare you the minimal details I have absorbed but only note that bark, like all living things, is…complicated.
Field guides to trees often use differences in the visual appearance of bark for identification, particularly of deciduous trees in the winter, though spring flowers and summer leaves provide more reliable clues. Here’s a partial list of kinds of bark that you might observe in a forest (or bush, as Pete would say), to assist in your identification of species. [A stray irreverent thought: why do we so need to label and classify things? Is that the best way to understand them?]
Human uses of bark are multifarious, even in industrial societies. Bark can cover and protect human habitations—just as it does trees. It is also used in many products, of which I can give only a few examples: spices and other flavorings (cinnamon), tannin (tanning), resin (lacquer, polish, wax), latex (rubber), medicines (quinine, aspirin), poisons (eucalyptus and manchineel), and of course corks for wine bottles. The phloem layers of some species is edible, though I wouldn’t try this without instruction. Bark has been used to make cloth, shoes, canoes, ropes and backpacks, and it has served as a surface for paintings and maps. Suburbanites spread bark mulch everywhere.
All of this is important, but photographers have a further interest in bark: its appearance. Pete and I share a common fascination with the look of bark, although our current set of examples is disjoint and limited: Pete lives in Perth, Australia, home to a dazzling array of gum trees (eucalypts), among others, and I live in western Virginia, home to a diversity of deciduous and evergreen trees. All our images are drawn from these locales, save for the California redwood and an orange eucalypt from Washington state. But both venues provide only a small sampling of the worldwide total of over 60,000 tree species! We are both entranced by the visual features of bark, such as the following. (This amateur analysis is only a pale sketch of the rich appearances of bark.)
Let’s start with color. For many casual observers, bark may seem dull and uncolorful; adding further insult, some drab and unstylish outdoor clothing gets the color label of “bark.” Granted, there are exceptions. For example, eucalyptus—I mean gum—trees sometimes have bright colors, including orange.
But in the main, trees aren’t vivid. I rather prefer to think of them not as drab but as understated, with many delicate shades of white, brown, gray and black in different species. Moreover, bark colors are quite worth exploring in different lights, as they will change in subtle ways.
Various other forms of life enliven the scene without harming the tree—lichen, moss, vines, epiphytes of all kinds. Tree bark is home to many species (botanists frequently call it a “substrate,” but I prefer the anthropomorphic “home”).
Bark excels in texture. Sometimes this texture is on the smooth side, with only specks of structure or pattern.
Other times bark peels off in small or larger plates, all with visual interest. 
But in most species bark can’t keep up with the constant growth of the cambium, and so it buckles and twists and deforms into furrows and ridges in infinite variety. You could spend an afternoon just scrutinizing the texture of one tree, minutely and carefully, from different perspectives, with different focal lengths and in different lights. Sometimes you can’t see the forest for the trees, but other times you can’t see the tree for the forest.
There are patterns in bark and also patterns of bark. Sometimes a tree’s bark is remarkably repetitious, with each ridge and furrow closely resembling the next.
Sometimes the bark of one tree is juxtaposed with the bark of another species.
And sometimes bark falls from trees and becomes a separate entity on the ground, forming structures and arrangements with other pieces of bark—or with twigs, plants, insects, animals and rocks.
Then, of course, there are the patterns that circumstance engraves or gouges. For example, burls bulge from trees struggling to contain an infection or damage.
Burrowing insects and their pursuers (such as woodpeckers) add smaller or larger holes, to the detriment of the tree’s health but to the delight of photographers.
Humans also add scars, especially on smooth bark: “JEDPEG” or “Kilroy was here” for example, or embedded fencing or logging mishaps.
Enough barking by me. Now it’s time to turn it over to Pete, and then we can both get outside to look at more trees. “Time spent among trees is never wasted” (Anon).
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