Trees are great storytellers. We just have to know how to read their clues.
Trees keep their stories hidden under a layer of bark. Not until a tree has fallen down can we read these tales. Trees tell their stories through their rings. Those rings tell the story of the tree’s life.
Counting a tree’s rings can tell you how old the tree is. Using tree rings to tell a tree’s age is called dendrochronology (from the Greek “dendron,” meaning tree limb, and “kronos,” meaning time). But each ring can also tell you more about each year of the tree’s life.
The oldest rings are in the middle of the tree. The outside rings, by the bark, are the youngest. The very center of the tree looks dark. It is called heartwood. The heartwood is dead layers of tree growth that are filled with sap. The heartwood works like a brace to keep the tree strong, supported and upright as it continues to grow year after year.
Surrounding the heartwood the wood is lighter. It is called sapwood. This newer growth is still alive. It works like a pipeline to bring water from the roots to the leaves.
In our area, trees only grow for part of the year: spring and summer. In tropical areas, trees are able to grow all year because the seasons don’t change and the weather stays warm. During their growing season, trees grow taller and wider. The wider growth can be seen as rings.
When you look closely at a tree stump you will see alternating dark and light rings. Light rings are called earlywood. Like the name suggests, earlywood shows the tree’s growth early in the season (spring). The darker rings are called latewood, and, you guessed it, they show the growth later in the season (summer). A light ring and dark ring together equal one year, so when you’re counting, only count the dark rings, which show the end of each growing year.
Let’s look at the patterns the rings make. Are they the same size? Are they even all the way around? Are there any markings? You’re probably noticing a lot of differences. Let’s find out what they mean.
Wide rings mean the tree had a great year. It received plenty of rain to help it grow, and good weather helped it have a long growing season.
Thin rings mean the tree had a difficult year. There could have been a drought (not enough rain) or a large amount of insects eating the leaves or causing other damage.
A ring that is wide on one side but thin on the other may mean the tree had something pushing against it that made it start to lean.
A very dark, thick spot is a sign of fire damage. Fire can scar the tree, but as years go by new growth will cover the scar.
A thicker line, or ruffle, running across the rings shows where a branch once grew before falling off. Like a scar from a fire, new growth will eventually cover the wound from the broken branch, and you won’t even be able tell there was damage — at least not until the tree falls, or is cut down, and you can read its story in the rings.
Now it’s your turn. Find a tree stump in a forest preserve, park or maybe even in your own yard. Look closely, and you will see the tree’s rings. If it’s hard to see each ring, trying wiping it with a wet cloth. Try to read the tree’s life story through its rings. You might want to use a magnifying glass to see all the details. While you are observing, ask questions:
Where is the heartwood?
Where is the sapwood?
How old is the tree?
How many good growing years did it have? How many difficult years?
Did this tree survive a fire?
Has the tree lost any branches? How many?
Maybe you want to know how old a tree is while it is still growing. You’ll need a flexible tape measure. First measure 5 feet high on the tree. Then wrap the tape measure all the way around the tree (circumference) at that height. Every inch equals about one year. It’s not as accurate as counting each ring, but it’s pretty close. Can you find a tree that’s the same age as you? Your parents? Your grandparents?
A tree’s rings tell its own story, but it also tells the story of the area around it – weather conditions, insect populations, fire and more. If you want to know more about the history of an area, remember to read the trees.
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