thumb|300px|[[Pinus ponderosa stump section timeline]]
Dendroarchaeology is a term used for the study of vegetation remains, old buildings, artifacts, furniture, art and musical instruments using the techniques of dendrochronology (tree-ring dating). It refers to dendrochronological research of wood from the past regardless of its current physical context (in or above the soil). This form of dating is the most accurate and precise absolute dating method available to archaeologists, as the last ring that grew is the first year the tree could have been incorporated into an archaeological structure.
Tree-ring dating is useful in that it can contribute to chronometric, environmental, and behavioral archaeological research.
The utility of tree-ring dating in an environmental sense is the most applicable of the three in today's world. Tree rings can be used to reconstruct numerous environmental variables such as temperature, precipitation, stream flow, drought society, fire frequency and intensity, insect infestation, atmospheric circulation patterns, among others. In 1929, American Southwestern archaeologists had charted a non continuous historic and prehistoric chronologies for the Chaco Canyon Region.
Methodology
There are two types of dates that can be assigned to tree specimens: cutting dates, and noncutting dates. Which date is assigned to a specimen is dependent on whether or not there is evidence that the last ring present on the specimen was the last ring the tree grew before it died.
For trees to be useful in archaeological analysis, they must "produce annual growth rings that are uniform around the tree stem", they must "live for decades and, preferably, centuries" and they "must have been used extensively by humans either for habitation or fuel." Another difficulty in the use of tree-ring dating as applied to archaeology is the variety and condition of wood used in construction of archaeological sites. Many such samples are encountered wet. Heartwood can normally retain much of its substance and can be dried out and polished for analysis. On the other hand, ancient wet sapwood samples seldom survive drying out. As a result, the sapwood should either be measured wet and then allowed to dry, or it should be frozen or kept wet.
Dendrochronological dating is potentially applicable wherever trees were growing, except in tropical regions. For use in absolute dating of archaeological sites, it is partially limited by the availability of a master reference chronology for the region concerned. If there is a gap in the chronology (e.g. the inability to use a chronology constructed from pine samples in the British Isle prior to the 17th century due to the lack of use of pine in architecture then) then absolute dating cannot be applied.
Dendroarchaeology has been used extensively in the dating of historical buildings. After cross-matching the chronology from the building with the chronology of living trees, it is immediately possible to figure out the dates at which the historic timbers used in construction were felled. Archaeologists at Chaco Canyon, New Mexico used tree-ring dating and found structure remains originated fifty miles south from the Zuni Mountains. Similarly, if an extended chronology is available, then dating of samples from buildings of known or unknown date is possible. However, a limiting aspect of this application becomes apparent when dating medieval buildings. In such buildings, many timber samples lack completeness out to the underbark surface which can make the task of determining the felling year much more difficult.
The application of dendroarchaeology in uncovering past trade patterns is based on determining the provenance of the tree-ring patterns. This is called dendroprovenance (or dendroprovenancing). Patterns from individual samples will match much more closely with chronologies of tree-ring series from the same area than with chronologies from other regions. For example, strong cross dating is found between Irish and English chronologies, but individual ring patterns tend to match better against their local chronologies. Hence, this strong geographical component of tree ring chronologies can be used to source timber samples at archaeological sites to uncover trade routes required for the site construction. and medieval times, but also to Kauri timbers from New Zealand.
Dendrochronology can also be used in concert with radiocarbon dating to allow for more accurate date measurements using radiocarbon dating on archaeological sites. It is known that the concentration of carbon-14 in the atmosphere is not constant. By performing radiocarbon dating on timber samples in a known chronology, radiocarbon dates can be plotted against real time generating a calibration curve that can be used for future radiocarbon samples.
While dendrochronology is often considered as an absolute dating method, it can also be used as a powerful tool in the relative dating of an archaeological site. Timber samples may be able to be compared with others on the site to help construct a timeline of events for that particular site. Such samples can also be used to settle issues in constructing a chronological typology for artifacts found on site. The important point is that such within-site analysis can be done whether or not a chronology is available to date the whole assemblage. Dendroclimatology is a sub-discipline of dendrochronology and dendroarchaeology that utilizes research methods for climate analysis. Dendroclimatology research has charted humidity changes in the American southwest since 1600.
See also
- Archaeology