TREE RINGS: A NATURAL DATA‐STORAGE SYSTEM
Authors: CREBER G. T. 
Published: January 2008

Summary1. The wood of trees grown in temperate regions shows a periodicity in the form of rings which, with certain known exceptions, accurately reflects the annual cycle of the seasons. The wood thus has a built‐in dating system.2. Tree rings are not always the same width in successive years; the widths show a positive correlation with variations in environmental factors.3. Trees in a given geographical area influenced by the same environmental conditions show similar patterns in their ring sequences and may thus be cross‐dated.4. Ring sequences from cross‐dated trees may be used to construct long, accurate chronologies. This practice, the science of dendrochronology, is now so reliable that it is widely used in archaeology and has also served to calibrate the14dating method.5. The extent of the variation in a ring sequence may be expressed in the form of a coefficient known as the mean sensitivity.6. The climatic effects recorded in the growth rings are those which operate at certain crucial periods, such as the growing season. The effects are primarily those of rainfall and temperature; humidity is usually only secondary.7. Damage by insects or fire may be dated by examination of ring sequences.8. As tree‐ring sequences correlate positively with contemporaneous meteorological data, they may be used in the reconstruction of past climates. This is the basis of extrapolatory dendroclimatology.9. New isotope techniques have been developed which indicate the possibility of deducing the ambient temperature of the tree's environment whilst its wood was being formed.10. Interpretative dendroclimatology aims to deduce from the features of a sample, or preferably from a number of samples of wood, the nature of the climate which influenced their development.11. The wood of most growth rings is divisible into two zones, earlywood and late‐wood. The former consists of larger, thin‐walled cells while in the latter the cells are smaller and thick‐walled.12. Beams of light, X‐rays and β‐rays have been used in various instruments to determine the earlywood‐latewood ratio.13. The earlywood‐latewood ratio is dependent upon genetic as well as climatic factors. Of the latter, summer rainfall is the most potent in producing latewood.14. The ring‐width data from a number of Recent and fossil wood specimens have been analysed to show that certain deductions may be made about the climate in which they were formed.15. A histogram technique has been devised to show differences between wood specimens with otherwise similar coefficients.16. Evidence has been produced in support of earlier work to the effect that ring‐width sequences from different radii of a tree trunk have fundamentally similar features, thus demonstrating ‘circuit uniformity’.17. The interpretation of the features of tropical woods is more complex. The mode of development of such a wood is the resultant of the interplay of genetical factors, endogenous rhythms and slight variations in environmental conditions.18. There is evidence that endogenous rhythms are also involved in the development of woods in temperate as well as tropical regions.