Browsing Tree-Ring Research, Volume 65 (2009) by Title
Now showing items 15-17 of 17
Research Communication: An International Tree-Ring Isotope Data Bank- A Proposed Repository For Tree-Ring Isotopic DataThe International Tree-Ring Data Bank (ITRDB) is an invaluable resource, providing access to a massive and growing cache of tree-ring data. Oxygen, carbon, nitrogen and hydrogen isotope treering studies, which have provided valuable climatic and ecological information, have proliferated for decades so an ITRDB expansion to include isotopic data would likewise benefit the scientific community. An international tree-ring isotope databank (ITRIDB) would: (1) allow development of transfer functions from extended isotopic data sets, (2) provide abundant tree-ring isotopic data for meta-analysis, and (3) encourage isotopic network studies. A Europe network already exists, but the international data bank proposed here would constitute a de facto global network. Associated information to be incorporated into the database includes not only the customary ITRDB entries, but also elements peculiar to isotope chronologies. As with the current ITRDB, submission of data would be voluntary and as such it will be crucial to have the support of the tree-ring isotope community to contribute existing and forthcoming isotope series. The plan is to institute this isotope database in 2010, administered by the National Climatic Data Center.
Tree-Ring Dating Of Old-Growth Longleaf Pine (Pinus Palustris Mill.) Logs From An Exposed Timber Crib Dam, Hope Mills, North Carolina, U.S.A.On 26 May 2003, intense rainfall from a series of thunderstorms in eastern North Carolina caused flooding that eventually destroyed the concrete dam in Hope Mills, draining Hope Mills Lake, and revealing a formerly submerged and buried structure that was identified as a timber crib dam. Inspection revealed these logs to be old-growth longleaf pines, which are now rare on the coastal plain landscape. Our primary objective was to develop a new multi-century longleaf pine tree-ring chronology by crossdating the tree rings from sections extracted from logs in the crib dam with an anchored tree-ring chronology created from nearby living longleaf pine trees. We also examined the climatic response in the longleaf pine trees to evaluate their potential for reconstructing climate. Using tree-ring measurements obtained from old-growth longleaf pines found at a nearby church, we were able to date the rings on 21 series representing 14 logs from the crib dam, spanning the years 1597 to 1825. Distorted sapwood in many of the logs prevented us from finding absolute cutting dates and lessened the strength of correlation during the period of overlap between the church series and crib dam series. Human disturbances, specifically related to the naval stores industry, likely influenced the growth-ring patterns of the crib dam pine samples, as well. Correlation analyses between the longleaf pine chronology and temperature, precipitation, Palmer Drought Severity Indices, and North Atlantic sea surface temperatures showed a significant response to cool and wet spring months.
Variance Stabilization Revisited: A Case For Analysis Based On Data PoolingThe traditional approach to standardizing tree-ring time series is to divide raw ring widths by a fitted curve. Although the derived ratios are conceptually elegant and have a more homogenous variance through time than simple differences, residual heteroscedasticity associated with variance dependence on local mean ring width may remain. Incorrect inferences about climate forcing may result if this heteroscedasticity is not corrected for, or at least recognized (with appropriate caveats). A new variance stabilization method is proposed that specifically targets this source of heteroscedasticity. It is based on stabilizing the magnitude of differences from standardization curves to a common reference local mean ring width and uses data pooled from multiple radii. Application of the method to a multi-site kauri (Agathis australis (D. Don) Lindley) data set shows that (a) the heteroscedasticity issue addressed may be generic rather than radius-specific, at least for some species, (b) variance stabilization using pooled data works well for standardization curves of variable flexibility, (c) in the case of kauri, simple ratios do not appear to be significantly affected by this cause of heteroscedasticity, and (d) centennial-scale variance trends are highly sensitive to the analytical methods used to build tree-ring chronologies.