Dating tree cores
This process indicated that the radiocarbon chronology underestimates the true ages of materials older than 2,000 years and that C dates must be corrected.The technique is based on the concept that each year (four seasons) a tree will accumulate one growth ring, and that that ring's attributes reflect the specific climatic regime of that year.
It has been reported that even relatively short-term maintenance of high water-deficit conditions would impact on the characteristics of tracheids by suppressing the capacity of the developing xylem to generate positive turgor, reducing wall extensibility and ultimately reducing cell expansion rates ().There are no studies on cork ring width variation in the first periderm, but the visual observation of stem discs with virgin cork show a decrease of ring width especially after around 20 years of age.Calculations of mean ring width for old virgin cork samples showed 0.95 mm for a sample with 93 years of age, and 0.85 mm for another sample with 183 years of age ().Therefore the growth curves of cork are analysed only in relation to the years with complete growth, and the first year of complete cork growth corresponds therefore to a traumatic phellogen in its second year of age.summarises the mean values of cork growth for the 8 complete years of growth in five sites in one region in Portugal (40 trees in each site).In the dry inner alpine valley, however, an irrigation experiment revealed that control, nonirrigated, trees presented tracheids with a wider lumen (a more effective water-conducting system) than control trees (Baas and Schweingruber, 1987; Woodcock, 1989; Sass and Eckstein, 1995; Sass-Klaassen et al., 2007; Pumijumnong and Park, 1999; Wimmer, 2002; Garcia Gonzales and Eckstein, 2003; Vaganov et al., 2006; Fonti et al., 2010; Drew et al., 2013; Xu et al., 2013 as an archaeological dating tool enjoyed tremendous expansion in the 1990s, particularly in western North America, Europe, Siberia, and the eastern Mediterranean, it is used wherever appropriate trees occur and a sequence has been established.
Most importantly, directly dated tree rings have been instrumental in the calibration of the radiocarbon timescale discussed below.
Based on the changes in radial cell diameter within the tree rings and the variation in ring width (), it is possible to extrapolate climate information, which is especially useful when coupled with information from megafossils, microfossils, and the sedimentological record of the site.
This approach has been utilized successfully by Parrish and Spicer in their work on Late Cretaceous floras from the North Slope of Alaska (Parrish and Spicer, 1988; Spicer and Parrish, 1990).
There are no research studies comparing for the same period the production of cork in one periderm and in successive periderms, and only a few singular cases are available for measurement.
One such example is shown in 150–200 years, it is estimated that the accumulated production of cork in trees with periodic removals of cork and periderm renewal is 3–5 times higher than the cork produced by the first periderm of a never debarked tree of the same age.
To take account of likely continual changes in atmospheric composition, it is almost a requirement that more sophisticated analyses be developed to interpret dendrochronological records. The discovery that sapwood converts to heartwood after a fixed number of years allows a retrospective analysis of tree leaf area, which together with stem diameter growth provides a reconstruction of individual tree and stand growth efficiencies backward in time.