• The Bootstrapped Response Function

      Guiot, J.; Laboratoire de Botanique Historique & Palynologie, UA CNRS (Tree-Ring Society, 1991)
      The bootstrap procedure provides a way to test the significance of the regression coefficients and the stability of the estimates in response functions generated by regression on principal components. A subroutine RESBO, which calculates a bootstrapped response function, has been added to Fritts' program PRECON.
    • Special Sanding Films and Sandpapers for Surfacing Narrow-Ring Increment Cores

      Yamaguchi, David K.; Brunstein, F. Craig; Mountain Research Station and Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado; U. S. Geological Survey, Denver, Colorado (Tree-Ring Society, 1991)
      Special sanding films (400 grit to 23 micron) and fine sandpapers (1200-1500 grit) can be used to surface increment cores containing narrow rings (e.g., >50 rings per cm) so that rings are clearly visible for microscopy and photography.
    • Dendrochronology of Abies Religiosa in Michoacan, Mexico

      Huante, Pilar; Rincón, Emmanuel; Swetnam, Thomas W.; Centro de Ecología, UNAM, Ciudad Universitaria, México; Laboratory of Tree-Ring Research, University of Arizona, Tucson, Arizona (Tree-Ring Society, 1991)
      An exploratory investigation of tree growth and climate relationships in Abies religiosa from Michoacan, Mexico, produced the first crossdated and standardized tree-ring chronology from the North American tropics. Pearson correlation coefficients and principal components response function analysis were employed. Results indicate that ring-width series from this species have moderately high signal-to-noise ratio (S/N = 13.42). A substantial percentage of the ring-width signal can be explained by instrumented monthly climate data, particularly spring precipitation and winter temperature. Although correlation between climate data and the tree-ring measurements indicate that growth of Abies religiosa is highly influenced by year-to-year climate variation, longer climate records and tree-ring chronologies are needed from this tropical region to improve understanding of climate -tree growth relationships, and for dendroclimatic reconstruction.
    • The Dendrochronological Signal of Pine Trees (Pinus Spp.) in Spain

      Richter, K.; Eckstein, D.; Holmes, R. L.; Institute of Wood Biology, University of Hamburg, Hamburg, Germany; Laboratory of Tree-Ring Research, The University of Arizona, Tucson, Arizona (Tree-Ring Society, 1991)
      Thirty-one old-age pine stands in nine mountainous regions of Spain were studied in order to delineate dendrochronologically uniform areas. A country-wide cross-correlation analysis of the autoregressively standardized site chronologies showed the dendrochronological signal decreasing with distance so that beyond about 450 km crossdating becomes less reliable, but even over 630 km, the correlation coefficient is sometimes significantly high. A principal components analysis of the variance among the site chronologies segregated the chronologies into a northern and a southern group roughly along a line from Madrid to Barcelona. Two low-elevation northern sites were grouped with the southern sites. Moisture supply limits the growth of the pines in this group. In contrast, the high-elevation northern sites do not suffer from prolonged droughts. According to the uniform and extensive tree-ring signal in the south of the peninsula, the potential of dendrochronology for dating cultural objects is predicted to be favorable. Because of the greater variability between sites in the north, further studies are necessary to delineate uniform areas.
    • Identifying Low-Frequency Tree-Ring Variation

      Sheppard, Paul R.; Laboratory of Tree-Ring Research, University of Arizona, Tucson, Arizona (Tree-Ring Society, 1991)
      I propose an approach to provide 95% confidence intervals for a chronology of low-frequency tree-ring variation so that a level of significance or importance for trends can be inferred. The approach also visually reveals the portions of a chronology in which sample depth is so poor that low-frequency variation is not robustly estimated. A key characteristic of the approach is that it is essentially a reordering of the individual steps commonly used in constructing standard tree-ring chronologies; consequently, it is computationally simple for researchers who already routinely construct standard tree-ring chronologies. The most important ramification of the approach is that each year of the chronology has a distribution of smoothed index values with which to estimate confidence intervals around the chronology of low-frequency variation. It can be argued that the approach constitutes multiple significance testing of means, which causes the α level for the confidence interval to be unknown. Nonetheless, the approach is still useful in that it provides a way to evaluate the probable importance of low-frequency trends expressed in tree-ring chronologies.