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Fifty-three ring-width chronologies have been developed from open-grown, low-elevation stands of Pseudotsuga menziesii (Douglas-fir) and Pinar ponderosa (ponderosa pine) in the southern Canadian Cordillera. These chronologies will be used to develop precipitation reconstructions for the region. The sites are unevenly distributed across the interior valleys from east of the Coast Ranges to the Canadian Rockies and from the Canada-U.S. border to the northern limits of both species. The chronologies range from 123-691 years (mean = 383 years) and, on average, have a strong within-chronology common signal (Expressed Population Signal > 0.85) with as few as eight trees. A Rotated Principal Components Analysis (RPCA) identified three regions within which annual ring-width chronologies covary similarly. A preliminary assessment of regional chronologies and patterns of extreme narrow and wide marker rings demonstrates that common growth variations exist in the chronology network that are probably precipitation related. Both the RPCA and marker ring analyses suggest distinctive regional patterns of growth on both interannual and longer timescales that vary through time and are possibly linked to persistent large scale climatic anomalies.

Atmospheric nuclear tests in the early 1960s introduced large amounts of radiocarbon into the atmosphere, which resulted in an increase of tropospheric ¹⁴CO₂ concentration by nearly 100% during the years 1964-1965. The bomb-produced ¹⁴C was then gradually incorporated within the global carbon cycle. The history of ¹⁴C concentration in the troposphere is preserved within annual growth layers of trees and can be reconstructed for those areas where direct measurements of 14C in the atmosphere were not performed. The paper presents results of ¹⁴C activity measurements in tree rings of tropical and subtropical species from Brazil, for the period 1945-1997. We investigated two species ( Araucaria angustifolia and Parkia sp.) growing at three sites covering the latitudinal band between 7 °S and 24 °S. The results indicate that the maximum ¹⁴C activity in the Southern Hemisphere occurred in 1965, with the Δ¹⁴C values reaching around 700%. Significant differences in Δ¹⁴C were recorded among the studied sites for the period of maximal ¹⁴C levels in the atmosphere, with the highest level observed at the tropical site and lowest in the subtropical zone. This reflects the dynamics of interhemispheric transport of ¹⁴C during the years of high spatial and temporal gradients of this isotope in the atmosphere.

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COFECHA is a computer program that assesses the quality of crossdating and measurement accuracy of tree-ring series. Written by Richard L. Holmes in 1982, the program has evolved into one of the most important and widely used in dendrochronology. It is important to note that COFECHA does not perform all the necessary steps in crossdating. Rather, the program is a tool that helps the dendrochronologist assess the quality of crossdating and measurement accuracy. The ultimate decision whether or not a tree-ring series is successfully crossdated must lie with the dendrochronologist and not with the software. Therefore, the program is most useful after initial crossdating is accomplished using visual or graphical techniques (such as skeleton plots), and the rings have been measured. The proper use of COFECHA adds a high degree of confidence that tree-ring samples have been crossdated correctly and measured accurately, ensuring that the environmental signal is maximized. In this paper, I describe the use of COFECHA through all necessary steps, and discuss the meaning of the initial questions posed at program start-up, the various options available in the main menu, the various sections of the output from COFECHA, and interpretation of the diagnostics of crossdating and measurement accuracy. I demonstrate methods used to help crossdate undated series, and offer tips on taking full advantage of the various options available in the program.

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