Correlations between climate variables and (a) the series of tree-ring carbon isotope discrimination (△<sup>13</sup>C), and (b) the first-order differenced △<sup>13</sup>C from the start of previous growing season (previous February) to the end of current growing season (current December) for the period of 1955–2013.
<p>SO represents the combination of data from September to October. The black (green) horizontal dash lines represent the 95% (99%) confidence level.</p
