Desiccation time during drought is highly predictable across species of Eucalyptus from contrasting climates

Catastrophic failure of the water transport pathway in trees is a principal mechanism of mortality during extreme drought. To be able to predict the probability of mortality at an individual and landscape scale we need knowledge of the time for plants to reach critical levels of hydraulic failure. We grew plants of eight species of Eucalyptus originating from contrasting climates before allowing a subset to dehydrate. We tested whether a trait-based model of time to plant desiccation tcrit, from stomatal closure gs90 to a critical level of hydraulic dysfunction Ψcrit is consistent with observed dry-down times. Plant desiccation time varied among species, ranging from 96.2 to 332 h at a vapour-pressure deficit of 1 kPa, and was highly predictable using the tcrit model in conjunction with a leaf shedding function. Plant desiccation time was longest in species with high cavitation resistance, strong vulnerability segmentation, wide stomatal-hydraulic safety, and a high ratio of total plant water content to leaf area. Knowledge of tcrit in combination with water-use traits that influence stomatal closure could significantly increase our ability to predict the timing of drought-induced mortality at tree and forest scales.