Drought sensitivity is climate-adapted and consistently influenced by wood density and maximum height in eucalypts

Rising drought frequency and intensity are placing many tree species at increasing risk of mortality. Identifying which trees are most sensitive to drought is critical for biodiversity conservation and forest carbon storage; however, this is challenging in natural and forestry systems because impacts are highly site-specific. Here we examine drought sensitivity in eucalypts, leveraging a common garden arboretum where 4733 trees from 1407 provenances and 821 taxa were exposed to an extreme drought. This allowed us to focus on the genetic constraints of drought sensitivity and trait variation, which is influenced by biotic and abiotic conditions in natural conditions. We addressed the following questions: (1) Is drought sensitivity associated with climate-origin? (2) Does climate-origin determine functional trait variability? (3) Which functional traits are better predictors of drought sensitivity? Additionally, we explored the effects of tree age and resprouting abilities on drought sensitivity. We found that drought sensitivity in eucalypts is climate-adapted, showing a strong association with Moisture Index (MI) of the source location (provenance). Species maximum height (H_max), wood density (WD) and leaf mass per area (LMA) were also associated with provenance aridity, demonstrating eucalypt climate adaptation. WD was the strongest functional trait associated with sensitivity, followed by H_max, while the effect of leaf traits was resprouting ability and age-dependant. The effect of leaf traits showed relevance when combined with other traits, as water use efficiency only decreased sensitivity for light wood, short-stature tree species. Adult trees showed higher sensitivity than young trees, while the sensitivity of different resprouting abilities was climate-origin-dependant. Our results provide unique insights into the genetic determinants of drought sensitivity in eucalypts. This forms a basis for the prioritization of species and areas for conservation and forest management. Read the free Plain Language Summary for this article on the Journal blog.