Stable isotopes of tree rings reveal seasonal-to-decadal patterns during the emergence of a megadrought in the Southwestern US

Recent evidence has revealed the emergence of a megadrought in southwestern North America since 2000. In this occasion I will talk about how 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 conditions during or before the establishment of the current megadrought. 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. Our results reveal the utility of tree ring δ¹³C to understand 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.