Free saxy chat - Dendrochronology cross dating
As soil water declines through the summer, the cells become thicker-walled and more dense.Thus each annual ring consists of early (light) and late (dark) wood. Douglass, the 'father' of dendrochronology was interested in the affect of sunspots on the earths climate.
Cores are glued to a grooved pieces of wood such that the tracheids were approximately 30 from their original vertical orientation, ensuring maximum visibility of the latewood to earlywood transition between successive years.
The wood is sanded with progressive finer paper to expose the growth rings for counting and measurement of ring width. The fundamental technique in dendrochronology is cross-dating, whereby distinctive series of narrow and wider tree rings are identified and matched among trees of different ages.
Tree-ring series can be classified as either complacent (uniform ring widths where moisture and heat are sufficient throughout the growing season) or sensitive (pronounced year to year variation in ring width, where conditions are frequently near the limits of the trees tolerance, e.g. The search for proxy climatic data was the original application of tree rings. In 1901, he noticed ring-width variations on a cut log and reasoned that these were controlled by the tree's environment (Fritts, 1976).
Douglass (1920) illustrated the relationship between climate and ring width by plotting both against time, and introduced the technique of cross dating by correlating ring-width signatures (sequences of wide and narrow rings) among trees distributed over large areas.
Delayed growth response to disturbance, and errors in tree ring counting caused by missing or false rings, prevent exact results.