Dead Again: Predictions of repeat tree die-off under hotter droughts confirm mortality thresholds for a dryland conifer species

Tree die-off, driven by extreme drought and exacerbated by a warming climate, is occurring rapidly across every wooded continent - threatening carbon sinks and other ecosystem services provided by forests and woodlands. Forecasting the spatial patterns of tree die-off in response to drought is a priority for the management and conservation of forested ecosystems under projected future hotter and drier climates. Several drought-related metrics have recently been proposed to predict the mortality threshold (i.e., tipping point) for Pinus edulis, a model tree species in many studies of drought-induced tree die-off. To improve future capacity to forecast tree mortality, we used a severe drought in 2018 across the southwestern United States as a natural experiment. We compared the ability of published mortality thresholds derived from four drought metrics (the Forest Drought Severity Index, the Standardized Precipitation Evapotranspiration Index, and raw values of precipitation and vapor pre...