A tree is a woody plant: a woody, tall-growing plant found in almost every country in the world. It consists of roots, a tree trunk, and a tree crown with deciduous or needle leaves. Many trees together form a forest.
Some trees live for hundreds of years, some even more than 1000 years. Trees can not only grow very old but also very large: The largest tree still alive today is the “Hyperion” sequoia with a trunk length of over 115 meters. It is located in Redwood National Park in California, USA.
Trees can be grouped in a number of ways. The most basic is the division into coniferous trees such as pine or fir and deciduous trees such as maple, birch, beech, chestnut, or linden. Our deciduous trees shed their leaves every autumn, only a few of the conifers do this, for example, the larches. A distinction is also made between tropical woods and others. The tropical woods have no growth rings and are often harder.
Near the equator, trees grow similarly throughout the year because there are no seasons. In other countries, trees grow faster in summer and slower in winter. This is what you see when you cut down a tree: the trunk shows rings that look like the waves when you throw a stone into the water, one on the outside of the other. These annual rings form because the tree grows quickly in summer. This creates a broad, light ring in the wood. In winter, however, only a narrow ring of harder, darker wood develops.
How do scientists use annual rings?
Any child can do the simplest scientific task: count the growth rings on a freshly felled tree or trunk. You already know how old the tree was when it was felled.
Often, however, one would like to know how old a building is. This can be determined by the wooden beams found in the building. You have to drill a hole in a beam and lift out the drill core. It has the shape of a long cone. You can see the annual rings on it.
In a good summer, each tree puts on a broader annual ring, in a bad summer, a narrower one. The scientists recorded this sequence in tables or graphics. If you now have such a drill core, you can compare it with the known tables and graphics. This way you can find out exactly in which year the tree was felled. Most often, a log was installed in a house one to two years after the tree was felled. How to find the year a building was built. This science is called “dendrochronology”. That comes from the Greek language. “Dendro” means “wood”. “Chronology” is the “time sequences”.