mirrored file at http://SaturnianCosmology.Org/ For complete access to all the files of this collection see http://SaturnianCosmology.org/search.php ========================================================== dendochronology Index tree_ring.gif (47294 bytes) Dendrochronology is the study and comparison of tree ring growths, which can provide very accurate dates about the wood itself or artifacts found in close proximity to it. Clark Wissler of the American Museum of Natural History first recognized the potential for using tree rings as a dating method. He worked with A. E. Douglass now considered the father of dendrochronology at the University of Arizona, on Pueblo Bonito, a pre-historic Native American settlement in New Mexico. Dendroarchaeology is the use of tree rings to date when timber has been transported, processed, felled or used in construction. Rings are made of xylem. Pith is found at the center of the tree stem followed by the xylem, which makes up the majority of the trees circumference. The cambium layer keeps the xylem separated from the rough bark. Each spring or summer a new layer of xylem is formed, producing the rings we can count. A tree ring is a layer of wood cells produced by a tree in one year, consisting of thin walled cells formed in the early growing season (called earlywood), and thicker walled cells that are produced later in the growing season (called latewood). The beginning of earlywood and the end of latewood forms on annual ring. In dendrochronology, these rings are then counted and compared. A departure of growth for any one year, as compared to average growth is known as a tree-ring chronology. Tree rings are never identical but the patterns are similar, assuming you are looking in the same geographic area. When the climate is particularly moist it will produce wider rings and in the dry years, narrow rings. Due to severe weather, trees may not produce a ring every year. To ensure they are counting accurately scientists have developed a cross check system that uses nearby resources to verify the data. By looking at a species with a known sequence of growth they can look for matching patterns in the unknown and perhaps see the past more clearly. In order for this to be a reliable method for dating, four factors must be present: 1. The species studied must only produce one ring per growing season or year. 2. Only one dominant environmental factor can be the cause of hindered or increased growth. 3. The dominant environmental factor should vary each year so we can see the changes clearly in every ring. 4. And lastly, the environmental factor must affect a large geographic area so testing can be compared easily (Stokes and Smiley 6). Factors Affecting Tree Ring Growth rustbul1.gif (274 bytes) Slope Gradient rustbul1.gif (274 bytes) Soil properties rustbul1.gif (274 bytes) Temperature rustbul1.gif (274 bytes) Wind rustbul1.gif (274 bytes) Sun rustbul1.gif (274 bytes) Snow Accumulation Ring sensitivity is the variation of ring growth that can be observed resulting from the above factors. Complacent rings lack this variation due to constant weather conditions. Wood of course is organic and will generally biodegrade when the tree cells stop growing. Animals feasting on it, air, bacteria or water will also speed up this process. Fortunately there are certain climates, like the Southwest, which slow the biodegradation process. Dry weather, water logging or fossilization preserve the wood for hundreds or thousands of years, making dendrochronology possible. In the Southwest U.S. archaeologists have found many cliff dwellings and were able to date entire villages and learn about their technology by using this method. Advances in the known chronologies are helpful for dendrochronologists. In the American Southwest bristlecone pine chronologies now extend 8,500 years. Work done in Germany and Northern Ireland has expanded the European oak and pine chronologies to over 11,000 years. Work in the Aegean over the past twenty years has produced about 6,000 years of chronologies over the past 9,500 years. Principals of Dendrochronology Uniformitarian Principal - We can link current environmental variability evident in tree ring growth to past environmental variability and use it to predict future environmental change. Limiting Factor Principal - The fastest rate that plant processes or growth can occur is equal to the greatest limiting factor. The Principal of Aggregate Tree Growth - Any individual tree growth series can be broken down into an aggregate of environmental factors, both natural and human, that affected the patterns of tree growth over time. Such factors can be: age related growth trends, the climate that occurred over the course of the year, and various factors that occur within the forest stand and outside of the forest stand. The Principle of Ecological Amplitude - Tree species will be most sensitive to environmental flux at the latitudinal and elevational limits of its range. The Principle of Site Selection - Sites can be identified and selected for based on the criteria that will produce growth rings series that is most sensitive to the examining factor. The Principle of Crossdating - Matching patterns in tree ring width, density, and other characteristics across several tree ring series allows for the identification of the year in which the growth ring was formed. The Principle of Replication - The environmental signal being examined can be maximized and the affects of other variables can be minimized by sampling more than one stem radius per tree and more than one tree per stand. References Kuniholm, Peter I. Dendrochronology. American Journal of Archaeology. Vol 99: no 1. Jan 1995. pg 99-102. Rice, Patricia C. Doing Archaeology-A Hands on Laboratory Manual. Mayfield Publishing Company, 1998. Stokes, Marvin A. and Terah L. Smiley. An Introduction to Tree Ring Dating. The University of Chicago Press. Chicago and London, 1968. Image Credit: From Doing Archaeology, a hands on laboratory manual. Patricia C. Rice. Mayfield Publishing Co. 1998 http://www.duke.edu/~cmg6/ http://tree.ltrr.arizona.edu/~grissino/princip.htm