Data from: Interactions between beech and oak seedlings can modify the effects of hotter droughts and the onset of hydraulic failure

Mixing species with contrasting resource use strategies could reduce
forest vulnerability to extreme events. Yet, how species diversity affects
seedling hydraulic responses to heat and drought, including mortality
risk, is largely unknown. Using open-top chambers, we assessed how, over
several years, species interactions (monocultures vs. mixtures) modulate
heat and drought impacts on the hydraulic traits of juvenile European
beech and pubescent oak. Using modelling, we estimated species interaction
effects on timing to drought-induced mortality and the underlying
mechanisms driving these impacts. We show that mixtures mitigate adverse
heat and drought impacts for oak (less negative leaf water potential,
higher stomatal conductance, and delayed stomatal closure) but enhance
them for beech (lower water potential and stomatal conductance, narrower
leaf safety margins, faster tree mortality). Potential underlying
mechanisms include oak’s larger canopy and higher transpiration, allowing
for quicker exhaustion of soil water in mixtures. Our findings highlight
that diversity has the potential to alter the effects of extreme events,
which would ensure that some species persist even if others remain
sensitive. Among the many processes driving diversity effects, differences
in canopy size and transpiration associated to the stomatal regulation
strategy seem the primary mechanisms driving mortality vulnerability in
mixed seedling plantations.