Piñon-juniper woodlands in southwestern United States have experienced two large-scale drought associated mortality events in the last century during the 1950's and 2000's. It has been suggested that many aspects of the recent 2000's drought, however, were novel. Changes in the quality of drought over time impose climate conditions beyond what most semi-arid tree species have evolved to tolerate. In this study we use annual tree rings and carbon stable isotope (δ13C) values from piñon pines (Pinus edulis) to assess legacy effects of the 1950's drought on survivor-ship during the 2000's drought in New Mexico. Our goal was to study the long-term and short-term variation among piñon pines along the drought-mortality continuum. Differences between trees’ responses in drought may determine the trajectory of post-drought recovery and or predispose trees to future mortality. Therefore, we sampled two groups of piñon pines during summer 2016. Cores were collected from remnant piñon pines that experienced the 1950's drought but did not survive the 2000's drought and from piñon pines that experienced and survived both droughts. Annual samples were taken from the late-wood and processed for carbon stable isotope analysis and compared with annual ring width and climate parameters.
Results/Conclusions
Mean ring widths between remnant and living trees did not differ pre-1940's. However, post 1940's the mean ring widths did significantly differ between the two groups with the remnant trees showing decreasing ring width over time. This finding suggests that after the extreme drought of the 1950's piñon pines growth diverged between the two groups. A similar difference between the piñon pines was also revealed in the δ13C values for annual bulk wood but only during years of high precipitation. Lower δ13C values were recorded for remnant trees that died and higher δ13C were recorded for alive trees in high resource years. Consequently, the piñon pines that supported higher levels of stomatal conductance in years of high precipitation experienced drought associated mortality in the future. This suggests that what drives individual level responses to multiple droughts is physiological performance in high resource years. Together these results highlight the importance of studying drought associated mortality as both a long-term and short term-process under timescales beyond experimental manipulation. Additionally, our results indicate that an individual’s response to previous events such as drought may underlie increased susceptibility to future droughts.