What do you picture when you think of how drought kills trees? Many picture dying conifers, which have also been at the heart of recently quantified drought legacies in forested ecosystems across the globe. Mortality and drought legacies (slow recovery from drought) are often studied at very different scales, but linking information from regional tree-ring networks and tree-level physiological measurements is essential to understand responses to future drought. Piñon pine (Pinus edulis) is an ideal species to investigate this, being well-represented in the International Tree Ring Data Bank (ITRDB), and the focus of a new precipitation manipulation experiment at the Sevilleta LTER. Here, we use ITRDB data to quantify how climatic memory—the temporal signature of tree growth responses to antecedent climate, encompassing legacy effects—has changed over the past century. We also are using radiocarbon (14C) to quantify the age of NSC within, and respired by, different tissues in piñon pine trees experiencing a range of drought stress (0%, existing 45%, 90%). A decade of 45% precipitation exclusion at the Sevilleta presents a rare opportunity to study the impacts of long-term drought stress on whole-tree carbon status and links to growth.
Results/Conclusions
Over the past century, pinyon pine’s memory of antecedent precipitation has lengthened, and its memory of temperature has shortened. Predicted growth responses of trees to extreme drought appear unchanged across this instrumental record (1900-2016), but contemporary trees are less severely impacted by repeated (compounded) droughts. We suggest growth is increasingly supported by reliance on old NSC reserves under more frequent drought in the southwestern US, corroborated by early results from the rainfall manipulation experiment. Trees exposed to 10 years of 45% precipitation exclusion contain younger NSC compared to control trees. Δ14C indicates NSC of deep sapwood in control trees is on average 16 years old, while deep sapwood NSC in droughted trees is on average < 10 years old, and in one tree is < 5 years old. Δ14C of carbon respired from branches and boles in droughted trees reflect younger NSC sources compared to control trees. Root NSC average age is similar in both droughted and control trees. Trees under long-term drought have thus already drawn upon old NSC in deep sapwood, but not belowground carbon pools. Remobilization of old NSC may thus provide resilience to drought, leading to changes in the memory of tree growth to antecedent climate.