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Tree Rings: A Timeline To History

By Edited Sep 10, 2015 6 16

A tree grows at different rates. In the spring and summer it grows more, and bands are light and wide. Growth slows in autumn, and during winter, it goes dormant and leaves a dark narrow ring. These tree rings provide a record of the past. The light and dark rings are a timeline to history.


Tree rings are a rainfall record during a year. During a wet year, a tree grows more, and makes the rings wider and light-colored. Years that have cool summer temperatures produce denser wood. This makes the light-colored bands of wood thinner. A researcher can tell what the area's climate was like hundreds of years ago by the thickness and density of the tree rings. Trees that grow in the same climate develop matching thick and thin ring patterns.

Other Climate Factors

Other factors influence tree growth and tree rings. The soil properties, wind, sun and location of the tree on a slope will affect growth rings. By noting the location and the climate influences on the tree, it is used to identify trees grown in similar conditions.


A tree grows one dark ring each year it's alive. Counting the dark tree rings gives the age of the tree when it died. By comparing tree rings of two contemporary trees grown in the same geographical and climate area, ring thicknesses may overlap, and sections of ring patterns match if they grew at the same time. This crossdating principle allows using tree rings to extend reliable dating techniques back over thousands of years.


Dendrochonology is the study of tree rings. A. E. Douglass developed the process of determining dates using tree-rings in the early 1920's. He founded the Laboratory of Tree-Ring Research at the U of A, University of Arizona in Tucson. Samples of tree-rings are stored at the university, and it has one of the largest tree-ring collections in the world. One source tree ring data is obtained is from trees that have been cut down. A section is cut from the tree and the tree rings counted. Live trees also yield data by core samples. A drill bit with a hollow shaft called an increment borer is used to remove a plug from a tree which shows the tree rings. These cores and sections continuously date tree-rings hundreds of years in the past. By matching site samples found with these known samples educators and scientists establish dates for the old wood in the same area.


Tree ring samples and dating have wide uses to determine climate and weather conditions in the past. It indicates the amount of carbon dioxide, forest population and other environmental conditions in the past. This allows archaeologists and others to establish dates for cities, settlements and past events.



Jan 14, 2011 1:26am
Wow! Very interesting!
Jan 14, 2011 9:46am
Jan 14, 2011 4:11pm
Sweet! Congratz on the front page. Tree ring info is fascinating.
Jan 14, 2011 9:11pm
Thanks for this interesting article. It is a pity that we forgot or didn't ever know to read the nature 'language' which is gorgeous and out there in front of us.
Jan 15, 2011 3:39am
Worthy of the front page. I've seen 1000 year old trees marked with key events, but this article shares info I never knew.
Jan 15, 2011 2:03pm
Fascinating information. Thanks for sharing this information with us!
Jan 15, 2011 4:10pm
Great information. Well written too.
Jan 15, 2011 7:25pm
greta feature piece. good job
Jan 20, 2011 7:06am
very informative piece of work:)
Feb 2, 2011 12:57am
This is a great article lots of info. Thumbs up!!
Feb 7, 2011 7:09am
congratulations on the feature article, trees are so fascinating, I always want to stop on the side of the road to draw them, they have so much character too them all very different in there own way.

Thanks for sharing that it was interesting and learnt something new too.
Mar 4, 2011 4:31am
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Apr 11, 2013 11:56am
Dendrochronology rocks. Just a minor correction: The Laboratory of Tree Ring Research is at the University of Arizona in Tucson (my alma mater), not Arizona State University.
Apr 11, 2013 4:32pm
Thanks for pointing out the error. At least I had it in the right state. Of course there's no rivalry between the U of A and ASU.
May 26, 2013 1:34am
Dendrochronology is a valuable tool for scientists, yet it is such a fascinating thought that trees are a 'window into our past'. Great article!
May 26, 2013 3:52pm
Thanks for the reading the article and the nice comment.
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