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Biology 103
2002 First Paper
On Serendip

How Bark is Protection for Trees

Jodie Ferguson

Bark: It is defined by the American Heritage Dictionary as "the outer covering of the woody stems, branches, roots, and main trunks of trees and other woody plants, as distinguished from the cambium and inner wood. Most of us can easily identify bark when presented with a question similar to: where is the bark? To answer such a question we will point to a tree, because trees are covered in bark. This seems very obvious and is. There is much about bark, however, that most people either do not know or have never taken the time to know or realize. I can name at least ten different trees off the top of my head, and although each has bark, each type of bark is different. Bark can be used as an aesthetic way to distinguish one tree from another; tree A had bark of a dark, flaky variety whereas tree B had bark of a pale, tightly covering the tree variety. When one looks at bark aesthetically, one misses the point of bark: that it is a protective device for the tree, and that its unique characteristics are functional.

The state tree of New Hampshire is the white birch. The bark of this tree is papery and white. As children, we would often peel off pieces and write to each other on them. The white color is supremely white—as white as this page. I was talking to my mother earlier this evening and she told me that the color of the bark is to reflect the winter sunlight—if the tree absorbs too much heat it will die. The white color of the bark prevents this from happening. The white birch tree is found in New Hampshire as well as other northern regions. It loses its leaves in the winter, thereby exposing its bark to the harsh sunlight of winter. The pale color of its bark allows the tree to survive.

One of the most famous types of tree in America is the redwood. These huge trees are found mostly in California, and are artifacts of an unsettled American wilderness. To further express how large these trees are: redwoods average eight feet in diameter and can be as wide as twenty feet. There are some as tall as 375 feet, which is taller than the Statue of Liberty. A typical redwood forest contains more biomass per square foot than any other area on earth, including the rain forests in South America. These trees are large. It would seem that they would be unharmed by anything in nature—could you imagine a beaver trying to chew through a twenty foot wide trunk? Still, there are things in nature that can harm these trees—namely, fire. A fire can burn any tree. Redwoods are not invincible, but they have evolved to avoid being burnt to the ground by the periodic fires the area experiences. The branches of the redwood do not start until very high off the ground—the branches are thinner than the trunk and therefore are more easily devoured by flame. Because the trees are so thick, nearing a foot thick in some trees, the fire chars the wood instead of burning through it. The charred wood acts as a heat shield and prevents the entire tree from being destroyed. Redwood trees can also withstand Redwood trees have been around since about the time of the dinosaurs. As we all know, not much has survived from that time. (1)

The Eucalyptus tree is to Australia as the redwood is to America. This tree is also found in California and other parts of the United States. The bark of the eucalyptus is very oily, so if it is caught in a fire the oil burns rather than the tree itself. The bark that is damaged by the fire sheds, so the tree does not catch on fire. There are also roots below ground that are very wet; their moisture protects them from the fire. There have been several reports of eucalyptus forests being completely burned, regenerating, being completely burned again, and regenerating again. To survive, the plant had to become resistant as possible to fire. That is what it has done. By being able to regenerate after a destructive fire, the plant adapts to a harsh climate. Other examples of plants that use fire to their advantage are the Jack pines, which have seritonous cones. This means that in order for the cones to open and go to seed, they must be exposed to direct and intense heat—that is, fire. Without the fire, the plant could not actually continue as a species.(2),(3)

Bark serves to protect a tree. Without bark, there would not be trees. Bark has its uses to humans as well as to trees: Native Americans used birch bark to build canoes and wigwams. The bark was also used to write on. There are oils in many different barks around the world that humans use. These same oils and other chemicals in the bark of trees and other plants can also serve to protect the plant. We are all familiar with poison ivy, one of the most irritating poisonous plants. There are also trees with poisonous bark—trees that we are somewhat familiar with. A few such trees with poisonous bark are the black locust, the yew tree, and the elderberry tree. There are many other plants that are completely poisonous, which would include the bark, but they seem to be smaller plants that do not necessarily have bark. A poison in the bark is a way to prevent being eaten by animals. (4)

We sometimes think of trees and plants as living things that are just there, passively accepting human interference and animal destruction. We often forget that trees have ways of being active organisms—they have ways of protecting themselves (obviously beyond the bark as well) that we rarely notice or think about. In discussions in class it has seemed that people have forgotten that trees are even living at all. It is important to recognize that such beings as trees do exist and are very necessary for human life. With all the protective devices trees have, they cannot withstand humans and their chain saws. We are hazardous to these plants. Perhaps if there were something akin to chain saws in nature, however, there would be plants whose bark was so tough and strong it could withstand such a cut. Despite the toughness of wood and bark, however, we have managed to create and build with the hardwood trees. With our tools we can almost anything with wood.(5) There is nothing stopping humans. Even trees will never have the chance to adapt to withstand us. They have developed as to withstand so much else that we should step back, stop cutting so many of them down, and admire their ability to continue with life even under the harshest conditions.

WWW Sources

1)Redwood Tree Information
2) Eucalyptus Tree Information
3) Jack Pine Information
4) Poisonous Plants
5) Interesting Use of a Hardwood

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