Tree-rings are wider or narrower, brighter or darker and they reflect conditions under which the tree grew, mainly the climate conditions.
The ring widths, the anatomical characteristics of the wood, and other features of their growth vary from year to year with changing environmental conditions.
We have an extensive collection of samples from the Aegean and Mediterranean for the last nine millennia, and a growing collection from northeastern North America, including samples from the Late Glacial chronozone.
We are developing methods for recording additional parameters, such as earlywood and latewood widths and densities, and maximum and minimum densities.
Facets such as vessel area and tracheid size are measured with image analysis.
Tree-rings are easy to observe in the cross-section of most sawn tree trunks.
Each ring is one of the many concentric bands surrounding the pith and all are more or less distinguishable from each other.
The context of the sample - whether from archaeological sites, a historic building, or a work of art - gives us a range of possible dates for the individual rings and the patterns contained in the rings.
Dendrochronology in general includes establishing calendar dates for samples and chronologies that include forest trees and historic sequences that securely crossdate; and establishing absolute dates for floating chronologies by securely crossdating the unknown sequences with other chronologies that are absolutely dated, or, if necessary, by radiocarbon wiggle-matching samples contained in the chronology.
Samples are collected by coring live trees, extant structural beams, boards, and rafters, and by taking cross-sections whenever possible.
For art historical objects and artifacts, the tree rings are measured directly on the object or from a digital photograph, both methods nearly non-destructive.
Well-known as the most precise dating method, dendrochronology enables us to study different aspects of the past with annual, and sometimes seasonal, precision over time.
Of the numerous definitions describing the essence of dendrochronology, here at the Cornell Tree-Ring Laboratory, we adhere to Eckstein's definition: "dendrochronology is a science of extracting chronological and non-chronological information from dated tree-rings." The key to dendrochronology and related sciences is tree-ring growth.
Cross-dating allows us to place sequences in time by matching the patterns securely, mainly with a visual inspection, using statistical tests to suggest possible relationships.