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What is Dendrochronology?

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  • Written By: Mary McMahon
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  • Last Modified Date: 03 November 2016
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Dendrochronology is a science which involves the study of growth ring patterns in trees, and using these growth patterns to establish a chronology of dates. In some areas, fully "anchored" chronologies lasting tens of thousands of years have been established by dendrochronologists through painstaking inspections of vast numbers of trees and lumber artifacts. Using dendrochronology, scientists can learn a number of interesting things about the natural environment and human history.

This science relies on the fact that living trees create distinctive layers known as growth rings for each year of life, and that each growth ring will vary in composition and appearance depending on the conditions at the time of the growth. During drought years, for example, a growth ring might be extremely slender, reflecting the fact that the tree didn't grow very much. In temperate years, a growth ring might be fat, reflecting ideal growing conditions for the tree.

By looking at the pattern of rings in a cross-section of tree trunk, a scientist can learn about the weather conditions that the tree witnessed. By analyzing isotopes and minerals from each growth ring, it is even possible to learn about volcanic eruptions and other major events in the area. Tree-ring dating can sometimes explain subtle cultural shifts spurred by climate change, making it of interest to anthropologists and archaeologists as well as scientists who are interested in the environment and climate change.

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While studying a single tree can certainly be interesting, the real science in dendrochronology lies in comparing trees across generations, using a distinctive growth ring as a marker to create a timeline. If, for example, 1873 created a characteristic growth ring, a scientist could find that ring in timber from a tree which grew from 1776 to 1897 and in a tree which grew from 1849 to 1913, thereby creating a timeline from 1776 to 1913. By looking for another distinctive growth ring in, say, 1812, the scientist could go further back with an older piece of wood or tree trunk, and so forth.

A dendrochronologist can use cut timber in dwellings and other structures for dendrochronology studies, along with whole tree trunks, fossils, and living trees. By studying the pattern of the tree rings, scientists can learn about climate change and the ways in which subtle changes have an impact on the natural environment. Dendrochronology is an especially fruitful period of study in desert conditions, where the environment preserves wooden artifacts; this may explain why the science originated in Arizona.

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stl156
Post 6

@titans62 - Good questions. I actually took a brief dendrochronology course one time to learn how to do the things you are talking about. It is actually a pretty detailed process.

Once they get the tree cores, they are mounted into grooves on long wooden blocks. Next, they have to be sanded down to give them a flat surface that easily distinguishes the different rings. Then they have special microscopes and measuring equipment that can take detailed measurements for the exact ring widths. They have special computer programs, too, that can analyze that type of information.

If you are really interested in dendrochronology, check out how to make skeleton plots. They are basically how the researchers match up the different rings from various trees like was mentioned in the article.

titans62
Post 5

@TreeMan - I agree with you. Dendrochronology for kids can be a great learning experience. I remember doing different activities like that when I was younger.

I am curious, though, how far back can dendrochronologists go with tree rings? What are the oldest trees that are out there? I am guessing probably the redwoods and sequoias, but I don't really know. If they had a tree that big, though, how would they ever be able to get a core that was big enough to look at in detail? I definitely don't think they are cutting them down to look at the rings.

Also, what is the whole dendrochronological process like? Once they get tree cores and stuff, what do they do with them? Are there any special techniques or anything that scientists use? If you wanted to study something like this, how would you go about it?

TreeMan
Post 4

I think making dendrochronology activities is one of the best ways to introduce children to things in nature. It is really a great learning experience for kids to see inside of a tree and put the pieces together that every ring means the tree is another year older. Then, they start to realize that most trees are very, very old. Hundreds of years in some cases.

Once they get a little older, another interesting thing to do is look at tree rings and pinpoint the years where different historical events happened and see how the tree has grown since then.

About the rings themselves, though, what exactly makes the annual rings? Why are there always light and dark bands?

Izzy78
Post 3

@anon186556 - Scientists can get tree cores from live trees with something called an increment borer. Basically, it is a long, hollow bit with some threads on the end of it, and it fits into another perpendicular piece to make a "t" shape. Then the person getting the core can just drill into the tree, and a core gets pushed into the hollow bit. They can pull out the core and then take it back to the lab to analyze.

There has been some controversy about whether or not taking out increment cores damages the trees or not. The hole itself will never kill the tree, but it might allow pathogens to enter easier. It really just depends on what

species of tree you are coring and the time of the year.

Almost every tree has some sort of pest or infection that can damage it, so it is important to know when those things are active and take the cores at different times. That way, the trees have time to heal the wound and prevent infection.

anon186556
Post 1

Very interesting article. I wanted more! Also, how can they study live trees?

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