Rapid and surprising dieback of Utah juniper in the southwestern USA due to acute drought stress

For nearly two decades, the American Southwest has been in grips of a long-term ‘megadrought’, punctuated by number short and severe ‘global change type droughts’ (i.e., negative precipitation anomalies co-occurring with high temperature). These events have caused widespread mortality drought-sensitive piñon pine (Pinus edulis) while co-dominant Juniperus spp. historically much more drought tolerant thus rarely died. However, occurred 2018 that rapidly (<1 year) canopy dieback osteosperma across vast area southeastern Utah. In order to uncover etiology behind this surprising event, we set up series survey plots captured gradients microclimate, topography, severity. We also quantified xylem hydraulic damage assessed presence various biotic agents declining junipers identify primary causes dieback. observed juniper was most (>60% dieback) at hot, dry, low elevation sites, associated drought-induced damage. There no evidence could be drivers dieback, implicating acute effects as main causal agent. The speed scale seems unprecedented region foreshadows an uncertain future for piñon-juniper woodlands continues get warmer drier.