Fig. 4

Annual ring-width variations per tree (grey lines) with the mean (black line, upper graph) and the standard tree-ring chronology (middle graph) from Aspidosperma tomentosum collected at San Julian, Santa Cruz, Bolivia. To emphasize the long-term variations, the chronology is shown with a cubic smoothing spline (red line) that highlights low-frequency variations over 15 years (Cook and Peters 1981). The variation in sample size over time is also shown in light grey. Finally, variations in the R-bar and EPS estimated over 50-year intervals are also shown for the interval 1900–2010 (lower graph)