The science of Dendrochronology (derived from the Greek words for “tree” – “dendro” and “knowing the time” – “chronology”) is a set of techniques by which the annual growth layers of trees can be assigned to a definite calendar year. The history of changes in the tree’s environment is reflected in various properties of the tree rings. These properties include ring width, cell size, wood density, trace element composition, and concentrations of stable isotopes and radioactive isotopes. External environmental variables affect the physiological processes that control tree growth and leave a permanent record in ring properties.
Tree-ring series can be used to reconstruct past variations in precipitation, river flows, temperature, soil moisture, the frequency of droughts, forest fires, major forest pest outbreaks, and other phenomena important to the management of natural resources and the natural and human environment. What can be reconstructed depends on those factors that limit growth. The reconstructions typically cover several centuries, but can occasionally extend to millennia and, as a result, be a valuable tool for researchers and managers in their quest to understand the variability of systems on timescales beyond the reach of conventional instrumental records. Such understanding can be especially important in regions such as the Mediterranean, where general circulation models project considerably increased aridity as a consequence of increasing greenhouse gases.