An introduction to tree ring dating pdf
Critical to the science, trees from the same region tend to develop the same patterns of ring widths for a given period of chronological study.Researchers can compare and match these patterns ring-for-ring with patterns from trees which have grown at the same time in the same geographical zone (and therefore under similar climatic conditions).Each ring marks a complete cycle of seasons, or one year, in the tree's life.In his Trattato della Pittura (Treatise on Painting), Leonardo da Vinci (1452–1519) was the first person to mention that trees form rings annually and that their thickness is determined by the conditions under which they grew. S., Alexander Catlin Twining (1801–1884) suggested in 1833 that patterns among tree rings could be used to synchronize the dendrochronologies of various trees and thereby to reconstruct past climates across entire regions.Direct reading of tree ring chronologies is a complex science, for several reasons.First, contrary to the single-ring-per-year paradigm, alternating poor and favorable conditions, such as mid-summer droughts, can result in several rings forming in a given year.
Growth rings result from new growth in the vascular cambium, a layer of cells near the bark that botanists classify as a lateral meristem; this growth in diameter is known as secondary growth.In addition, some genera of trees are more suitable than others for this type of analysis.For instance, the bristlecone pine is exceptionally long-lived and slow growing, and has been used extensively for chronologies; still-living and dead specimens of this species provide tree-ring patterns going back thousands of years, in some regions more than 10,000 years. P., the radiocarbon dates are calibrated against dendrochronological dates.When one can match these tree-ring patterns across successive trees in the same locale, in overlapping fashion, chronologies can be built up—both for entire geographical regions and for sub-regions.
Moreover, wood from ancient structures with known chronologies can be matched to the tree-ring data (a technique called cross-dating), and the age of the wood can thereby be determined precisely.
The rings are more visible in trees which have grown in temperate zones, where the seasons differ more markedly.