The interpretation of archaeological tree-ring dates
Ahlstrom, Richard Van Ness
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A comparative approach to analysis of the body of tree-ring data from prehistoric sites in the American Southwest provides information on patterns of wood use, the effectiveness of interpretive methods, and culture history. Requisite to this approach is an interpretive framework developed since the 1920s by archaeologist versed in tree-ring analysis. Central to this scheme is indirect dating, by means of which dates derived from biological events of tree growth are applied to progressively more remote events in human history. A new contribution to this framework is an interpretive model that focuses on the shape of tree-ring date distributions. The framework guides re-interpretation of tree-ring data from sites categorized as mogollon 2 through 4, Basket maker III, Pueblo I, Pueblo II, Chaco, Pueblo III, Western Pueblo, Rio Grande, and Pueblo V, and from late pithouses and miscellaneous kivas. Coverage is relatively comprehensive for pithouse sites, Pueblo I sites, and kivas, but selective for post-Pueblo. Interpretations assign dates to construction and repair events, identify data from deadwood and from eroded, stockpile, and reuses beams, demonstrate the usefulness of detailed provenience information on individual tree-ring samples, and evaluate tree-ring data for reconstructing structure and site histories.The potential contribution to culture history of the corpus of tree-ring dated events is illustrated through discussion of 213 dated pitstructures. This body of data also contributes to knowledge of past wood use and to understanding of interpretive methods. Thus, dates from firewood samples tend to predate hearth use dates, "v" dates are close or equal to cutting dates, and "++" dates are useful though imperfect indicators of deadwood use. Construction-repair intervals indicate that pithouses typically survived for less than 20 years, no such limitations applies to divas. A sample of 20 or more dates is usually adequate for dating pitstructure, as the sample falls below this level, unless patterning is clearcut, dating confidence decreases. Patterning in date distributions suggests that many sites were abandoned within a decade or two after their latest tree-ring date.