Samstag, 25. Oktober 2008


Tree-rings of Picea, showing the annual growth rings with the brigth, and wider earlywood, and the darker latewood.

Dendrochronology deals with the dating and the study of the annual growth layers in woody trees and shrubs - appropriately claimed tree-rings. In temperate climates, with a growth period (spring-summer, the produced wood is the so called earlywood) and a rest phase (autumn-winter, the so called latewood) with no or very low growth, trees produce annual rings. Counting this annual rings, the age of the studied plant can be determinate.

Comparing the wide of the rings, claims about annual growth factors affecting the plant can be argued, like temperature, precipitations or competition. In the early fifteenth century, Leonardo da Vinci noted tree rings as annual patterns, and recognized a relationship between tree ring widths and precipitation.
In the following centuries the anatomy and ecology of tree rings were studied in detail. In 1904, the American astronomer Andrew Ellicott Douglass (he later founded the Laboratory of Tree Ring Research, University of Arizona), developed a tree ring chronology for the south-western United States, using the narrow tree rings found in Ponderosa pine trees, caused by droughts, to corelating different, individual trees. By 1914, he showed in a 500-year record a positive correlation between ring width and precipitation. He then used this chronology to date wood samples found in the Indian pueblo sites, affirming dendrology as dating method.
Joined in his studies by Edmund Schulman, they tried to improve and lengthened the tree ring record, discovering the (until then) oldest known trees of the world, the over 4.000 year old bristlecone pines in the Californian White Mountains. The bristlecone pine chronology, and so the climatic reconstruction, now dates back to 8.500 years. This methusalems were also used to calibrate the 14C curve (influenced by the atmospheric relationships of the carbon-isotopes).

Bristlecone pine (Pinus longaeva)


SMITH & LEWIS (2007): Dendrochronology. in ELIAS (ed.) (2007): Encyclopedia of Quaternary science: 459-465

1 Kommentar:

Silver Fox hat gesagt…

You should have entered our little tree meme!