Dendrochronology – Tree Rings and Dating

Dendrochronology – Tree Rings and Dating

Anyone who has ever been around wood for even the minimal amount of time have seen the rings at the end of a board or piece of firewood. Many people never think much of these rings and continue on with the work at hand. They have never given any thought to what these growth rings could tell them about a piece of wood. The growth rings are clearly visible on most tree species as there is a wide, light colored area of  “early wood” which is added during the rapid growing season of late spring and summer.

When the growth slows down in the Fall, a very narrow, dark ring is formed and this is called “late wood”. Generally speaking¸ one growth ring means one year of growth. This is not completely so as some species,such as southern yellow pine have a second and even a third flush during the growing season. These flushes result in a faint growth ring(s) between the more prominent late wood rings. These rings are formed when the growth slows down for a period of time and then takes off once again. In the tropics where temperatures and rainfall are adequate for year around growth, growth rings are not formed. This would be the case of palm trees.

In temperate regions, cottonwood and aspen do have growth rings but they are very hard to discern. In the temperate regions of the world, the width of growth rings can be dependent on growing conditions as well as competition from other trees growing close to them. If a tree had too much competition from surrounding trees, then the growth rings will be very close together. If these trees are removed from competition by disease of cutting, then the remaining tree(s) will show a spurt in growth. This was the case when the chestnut blight moved though the eastern United States and removed competition to the remaining oak, pine and hemlock.  

In the Southwest and other arid regions, the abundance or lack of rain can be a direct correlation to the width of growth rings. As vegetation in these areas is sparse rainfall is the main contributor to the growth rate of species. Dr. A.E. Douglass discovered these patterns of growth rings that were indices of weather patterns. He spent much of his life studying these patterns and thus was formed the science of dendrochronology. The study of these growth ring phenomena coupled with carbon dating has done much to dating the ruins of paleo-man in the Southwest. It has also told us about weather patterns, glacier advances and patterns of fire in the forests of the United States.  

From something as simple as rings etched into the cross section of a tree a whole new science has developed which aids man in understanding the civilizations and weather patterns from thousands of years ago. In fact, one bristlecone pine in the mountains of Nevada was found to be over 5,000 years old and the growth rings have lent additional knowledge about climate of that area. Who knows what discoveries lie just around the corner from the diminutive growth rings of trees!

Source by Clyde Cremer
#Dendrochronology #Tree #Rings #Dating speaking tree

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