Tying tree ring fragments in the tools to established chronologies, Bill and Daly (2012) discovered that all three of the mounds were opened and the grave goods damaged during the 10th century, likely as part of Harald Bluetooth's campaign to convert Scandinavians to Christianity.
Lübeck's medieval history includes several events that are pertinent to the study of tree rings and forests, including laws passed in the late 12th and early 13th century establishing some basic sustainability rules, two devastating fires in 12, and a population crash between about 13 resulting from the Black Death.
It had long been known that three 9th century Viking period boat-grave mounds near Oslo, Norway (Gokstad, Oseberg and Tune) had been broken into at some point in antiquity.
See the cal BP discussion for additional information about radiocarbon calibration.
Tree-ring dating works because a tree grows larger--not just height but gains girth--in measurable rings each year in its lifetime.
Evergreen cambiums are commonly irregular and not formed annually.
Trees in arctic, sub-arctic and alpine regions respond differently depending on how old the tree is--older trees have reduced water efficiency which results in a reduced response to temperature changes.Ideal trees for analysis grow in exposed situations, often on infertile soils, where they lack competition with other trees and therefore show a more direct growth response to climatic variation.If conditions become too harsh, however, false and missing rings may occur; these must be recognized by analysis of replicate cores or cross sections.Not all trees can be measured or used without additional analytical techniques: not all trees have cambiums that are created annually.In tropical regions, for example, annual growth rings are not systematically formed, or growth rings are not tied to years, or there are no rings at all.Features such as wood density, the elemental composition (called dendrochemistry) of its makeup, the anatomical features of the wood, and stable isotopes captured within its cells have been used in conjunction with traditional tree ring width analysis to study air pollution affects, the uptake of ozone, and changes in soil acidity over time.