Kids and Critters: Learn how to read a tree

From small to tall, each one has a tale to tell

  • Each arrow in this photo points to an interesting event in this cottonwood tree's life. The red arrows indicate injuries and the blue arrow indicates an area where competition is occurring. Bill Danielson photo

Published: 3/6/2016 4:21:52 PM

To the west of my house stands a beautiful cottonwood tree. I’ve probably looked at this tree a thousand times during all seasons of the year, but recently I saw it from a slightly different perspective and noticed something very interesting. Here and there the trunk changes direction, which points to some interesting events in the life of this particular tree.

Trees grow from the very tips of their branches in a very special region of tissue known as the apical meristem. You may be more familiar with the term “bud,” which does indeed contain a meristem. This is where the plant cells are dividing and elongating at a quick pace and there is usually one particular meristem that becomes the leading tip of a growing tree. Other buds (containing meristems) occur off to the sides of the main stem and when they grow they become the branches of the tree.

Since trees are plants, which need sunlight, it makes sense that all trees grow upward toward the sky. I’m forced to generalize a bit here, but different groups of trees have developed different mechanisms that allow them to accomplish this feat and although each species is different, they all start off by growing as straight and as tall as possible.

In a perfect world with perfect weather conditions many trees would grow as straight as an arrow, but we all know that the weather can turn nasty from time to time. Storms with strong winds, or ice storms in the winter, can damage tree branches. So what happens to a tree if the leading tip of the trunk is broken off?

Well, this is where the side buds that usually become the branches start to respond to the emergency. If the main stem is injured, the branches will start turning upward and will compete for dominance. At some point, one branch will win and assume the role of the main stem. But because only the tips of the branches can actually get longer, the path that they take is recorded in their shapes. Thus, if you know what to look for you can read the history of a tree in the shape of its branches and trunk.

Take my cottonwood tree as an example. I have added three arrows to draw your attention to the recent events in this tree’s life. The bottom arrow points to a spot where the leading stem must have been broken. If I think back many years I recall that there was a severe ice storm that might explain what happened to this tree. This is the point where the trunk splits because this is the point where two different branches started to compete for dominance.

Go up to the next arrow (the blue one) and you will see an area where the various branches on this left-hand stem are still competing for the role of the new trunk. Two are trying to grow straight upward, but one appears to be a little taller than the others and may take over the leading role.

On the right-hand stem there is even more evidence for damage from later storms. The third arrow points to a spot where the leading stem was again injured and the stem splits into another “y” shape. The “main” stem bends to the right, but at the leading tip of that split the branch is straightening out and assuming the role of the main trunk.

With the sun rising a little earlier each morning this is the perfect time of year to look at the shapes of trees on the way to school. Look for perfectly straight trees and you will be surprised at how few you actually find. Many trees bear the scars of past injuries and the evidence of the timing of these injuries is locked in the shape of their trunks and branches. All you have to do is learn to “read” a tree and the world will become a much more interesting place for you.

Bill Danielson has worked as a naturalist for 16 years. In that time, he has been a national park ranger, a wildlife biologist and a field researcher. He currently works as a high school chemistry and biology teacher. His Speaking of Nature column runs weekly in The Recorder, except for the first Monday of each month, which is when his Kids and Critters column for young readers appears. To contact Bill, or to learn more about his writing, visit www.speakingofnature.com.




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