Bark: An appreciative look at the skin of our trees

  • Article by: CONNIE NELSON , Home
  • Updated: March 27, 2009 - 10:10 AM


Photo: Tom Wallace, Star Tribune

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Consider a tree in winter. Blossomless, leafless, seemingly lifeless.

But if you look a little closer, you'll see that each barren tree is actually shrouded in an elegant skin, a protective covering that has texture, pattern and color.

Though it is more subtle than fragrant apple blossoms or fire-red fall leaves, bark has a beauty all its own. The thick and deeply gnarled cottonwood, the papery, peeling river birch, the copper-colored amur chokcherry all boast bark that is unique to its species and captivating to a growing number of gardeners.

"There's a certain inherent beauty in a tree that doesn't have foliage on it," said Patrick Weicherding, an associate professor of horticulture with the University of Minnesota Extension Service. "Look at a bur oak in winter. It's majestic. There's nothing like it."

Gardeners have long appreciated bark -- perhaps most often in the form of mulch. But with the growing desire to create attractive winter landscapes, bark is coming out from behind the shadows cast by flowers and foliage.

"People are becoming aware of winter interest," said Nancy Rose, a research horticulturist with the Minnesota Landscape Arboretum, "and bark is certainly a part of that."

It was our long and comparatively bleak winters that made a bark aficionado out of Diana Thottungal. A naturalist at Eloise Butler Wildflower Garden and Bird Sanctuary in Minneapolis' Theodore Wirth Park, Thottungal learned to use bark to identify trees.

"It [winter] is awfully barren for an awfully long time," she said. "What's left? The bark of trees. Bark is an easy way of sorting out what kind of tree you're looking at. But there's also a real aesthetic there. It's beautiful."

Bark is prized for its patterns and textures, celebrated for its surprising range of colors and noted for its variation -- not only within a single species, but within a single tree. On an older poplar, for example, the bark on the lower part of the trunk may be thick, heavily ridged and almost black. Higher up on the trunk or in the branches, the bark is smoother and much lighter in color.

Bark also has staying power that flowers and foliage do not. According to Gary Johnson, associate professor of urban and community forestry at the University of Minnesota, bark offers "365 days of appreciation. I think it's weird to focus on flowers, especially on trees," he said, noting how quickly spring blossoms fade. "I always opt for, 'What's the fruit like?' 'What's the fall color like?' 'What's the bark like?' "

In fact, aside from the few northern trees that shed, bark is so long-lasting that when you look at many trees, what you see is an accumulation of many years of bark growth.

Bark basics

Bark is a nontechnical term that refers to the outer covering of a tree, shrub or woody stem. What we call bark is actually made up of many layers. The inner bark is the tree's life support system and is responsible for new growth and for conducting food, water and oxygen throughout the tree.

Outer bark is essentially dead. But it, too, is indispensable because it protects the tree from disease, injury, insects and animal pests. It can act as an insulator against heat or cold and, in some trees, as a fire retardant. Douglas fir, red pine, western larch and many species of oak have bark that protects against fire.

Bark also provides protection for a wide range of insects that live in tree bark as well as those that use bark as camouflage. Several species of moths, beetles and even a few amphibians have taken on the dappled colors of bark to protect themselves from predators. And a host of exotic-looking lichens, moss and fungi make bark their home.

For human consumption

Humans have found countless uses for bark -- harvesting rubber, cork and cinnamon from tree bark and producing varnish, shellac and lacquers as well as frankincense and myrrh from pine resin. Medicines (including quinine, an early treatment for malaria) and poisons (such as curare) are derived from bark. Bark has been used to make cloth and canoes. And the tannins widely found in bark have been and still are being used in tanning leather, processing food, ripening fruit and making some cocoas, teas and wines.

But one of the more recent -- and less intrusive -- uses of bark is its visual appeal.

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