Recent evidence has revealed the emergence of a megadrought in southwestern North America since 2000. Megadroughts extend for at least 2 decades, making it challenging to identify such events until they are well established. Here, we examined tree-ring growth and stable isotope ratios in Pinus ponderosa at its driest niche edge to investigate whether trees growing near their aridity limit were sensitive to the megadrought climatic pre-conditions, and were capable of informing predictive efforts. During the decade before the megadrought, trees in four populations revealed increases in the cellulose δ¹³C content of earlywood, latewood, and false latewood, which, based on past studies are correlated with increased intrinsic water-use efficiency. However, radial growth and cellulose δ¹⁸O were not sensitive to pre-megadrought conditions. During the 2 decades preceding the megadrought, at all four sites, the changes in δ¹³C were caused by the high sensitivity of needle carbon and water exchange to drought trends in key winter months, and for three of the four sites during crucial summer months. Such pre-megadrought physiological sensitivity appears to be unique for trees near their arid range limit, as similar patterns were not observed in trees in ten reference sites located along a latitudinal gradient in the same megadrought domain, despite similar drying trends. Our results reveal the utility of tree-ring δ¹³C to reconstruct spatiotemporal patterns during the organizational phase of a megadrought, demonstrating that trees near the arid boundaries of a species’ distribution might be useful in the early detection of long-lasting droughts.

最近的证据表明，自 2000 年以来，北美西南部出现了特大干旱。特大干旱至少持续了 20 年，这使得在此类事件完全确定之前确定此类事件具有挑战性。在这里，我们检查了黄松最干燥生态位边缘的树轮生长和稳定同位素比率，以研究在干旱极限附近生长的树木是否对特大干旱气候先决条件敏感，并能够为预测工作提供信息。在大旱前的十年里，四个种群的树木显示出早材、晚材和假晚材的纤维素 δ ¹³ C 含量增加，根据过去的研究，这与固有水分利用效率的增加有关。然而，径向生长和纤维素δ¹⁸ O 对大旱前的条件不敏感。在大旱前的 20 年里，在所有四个地点，δ ¹³ C 的变化是由针状碳和水交换对关键冬季月份干旱趋势的高度敏感性引起的，而四个地点中的三个地点则是在关键的夏季月份. 这种大旱前生理敏感性对于接近干旱范围限制的树木来说似乎是独一无二的，因为在位于同一大旱域中沿纬度梯度的十个参考地点的树木中没有观察到类似的模式，尽管干燥趋势相似。我们的结果揭示了树木年轮 δ ¹³的效用C 重建特大干旱组织阶段的时空模式，证明靠近物种分布干旱边界的树木可能有助于早期发现长期干旱。