Retrospective analysis of wood anatomical traits and tree?ring isotopes suggests site?specific mechanisms triggering <i>Araucaria araucana</i> drought?induced dieback

In 2010–2018, Northern Patagonia featured the longest severe drought of last millennium. This extreme dry spell triggered widespread growth decline and forest dieback. Nonetheless, roles played by two major mechanisms driving dieback, hydraulic failure carbon starvation, are still not clear understudied in this seasonally region. Here, for 1800–2017 period, we apply a retrospective analysis radial growth, wood anatomical traits (lumen area, cell-wall thickness) ?13C ?18O stable isotopes to assess dieback causes iconic conifer Araucaria araucana. We selected three stands where declining (defoliated) nondeclining (not defoliated) trees coexisted along precipitation gradient from warm-dry Coastal Range cool-wet Andes. At all sites showed lower theoretical conductivity, suggesting long-lasting process deterioration their water transport system compared nondeclining, coexisting trees. Wood evidenced that divergence between started at least seven decades before canopy drier stands, higher water-use efficiency (WUE) throughout whole which attributed early stomatal closure, greater starvation risk consistent with thinner cell walls. wettest stand, found opposite pattern. reduction WUE coupled thicker walls suggested increased assimilation rates exposure drought-induced failure. The values indicated different strategies gas exchange sites, likely consequence microsite conditions sources. Multiproxy, quantifications xylem tree-ring provide robust tool identify forecast, or will show or, on contrary, withstand be more resilient future hotter droughts.