Chapter 13 - Tree Rings

Abstract

Variations in tree ring widths from one year to the next have long been recognized as an important source of chronological and climatic information. The mean width of a ring in any one tree is a function of many variables, including the tree species, tree age, availability of stored food within the tree and of important nutrients in the soil, and a whole complex of climatic factors (sunshine, precipitation, temperature, wind speed, humidity, and their distribution through the year). The problem facing dendroclimatologists is to extract whatever climatic signal is available in the tree ring data and to distinguish this signal from the background noise. Climatic information has also been obtained from density variations, both inter- and intra-annually (densitometric dendroclimatology), and isotopic variations in wood have been studied as a possible proxy of temperature or precipitation variations through time. Despite the complexities of fractionation both within the hydrological system, and in the trees themselves, detailed isotopic analysis of wood from tropical trees, in which distinct annual rings may not be clearly visible, has provided new insights into growth rates and climatic variations over recent centuries.