The key is found in linking growth curves together, using old living trees to make connections to sawn lumber, timbers in buildings, and old furniture. Going back to our example of that 200-year-old pine: Imagine that there is a 150-year-old house nearby, built of timbers cut onsite. Many of those timbers came from trees that were likely far older than our standing grandfather pine, with which they share 50 years of overlap in their growth curves. Once that overlap is confirmed, it becomes possible to count backwards in the rings of the old house timbers and create an extended chronology. Utilizing local structures and archaeological finds in this way, a regional “master chronology” can be built that extends many centuries into the past.
Of course, areas of the world that feature very old living trees are at a great advantage in that the entire chronology can be established with just a few samples. The bristlecone pines of the southwestern United States give an extreme example, as the most ancient living tree is nearly 5,000 years old. Utilizing cross-dating methods in analyzing dead pines found in the area (which decay very slowly), a complete chronology extending 9,000 years has been established there. For archaeologists, this offers tantalizing opportunities to precisely date many wooden artifacts and ancient structures found in the area and to accurately calibrate radiocarbon dating; for climatologists, it represents a treasure trove of information on snowpack trends, temperature, and atmospheric conditions over millennia.
–Michael Updegraff, excerpt from “Scribes of Nature: Dendrochronology & the Deeper Story of Wooden Objects,” in Issue Nine