What the Trees Can Tell Us

Many of us have learned that you can tell how old a tree is by counting its “rings.”  Tree-ring dating, or dendrochronology, was first discovered by Andrew Ellicott Douglass, an American astronomer who was born on July 5, 1867.

In 1894, Douglass reported his observation that tree rings were thinner in years with sunspot activity.  He was contacted by naturalist Clark Wissler, who was trying to determine the age of archaeological ruins in the American Southwest.

Over the next 15 years, the two men compared wooden beams excavated from various ruins, trying to cross-date them by comparing the rings.  Finally, in 1929 Douglass succeeded in assembling a continuous record of tree-ring data all the way back to the year 700 AD.  He predicted that his discovery would be “destined to hold a place comparable to Egypt’s Rosetta Stone.”

Dendrochronology works because a tree grows a measurable ring of new cells each year in its lifetime.  The technique is so precise, it is used to calibrate radiocarbon dating.  (Not all trees can be dated this way.  Some trees, including evergreens and olive trees, do not have annual growth rings.)

Scientists have used dendrochronology to reconstruct historical events including fires, hurricanes, volcanic activity, glacial movement and precipitation.

Researchers from the Slovak and Czech Republics studied how various weathering and environmental factors can affect the ageing of wood.  They used an Agilent HPLC chromatograph for sample analysis and Agilent ChemStation software for data collection.

Dendrochronology is also used as a tool against illegal logging, where authorities can match the ring “fingerprint” of tree stumps against lumber samples.  Researchers in Poland demonstrated that DNA markers can also be a precise and suitable tool.  They used an Agilent Bioanalyzer System and Agilent software to perform their genotyping.


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