Is intrinsic water-use efficiency an early predictor of adult growth in sessile oak (Quercus petraea Matt. Liebl) high forest stands?

Context : In a context of increasing droughts, identifying the causes of variations in individual growth performance is crucial. Aims : We investigated whether early-life intrinsic water-use efficiency (iWUE), and its plasticity to drought, estimated from tree-ring δ 13 C, can predict long-term growth performance in sessile oak trees. Methods: Two mature stands with contrasting ecological and management contexts were studied: (i) a fertile, high-density stand without thinning since a century, and (ii) a low-density stand, undergoing chronic drought-related dieback. All trees in both plots (n ~ 100 per plot) were cored, enabling reconstruction of the whole within-population variability of iWUE and radial growth trajectories. Results : Although the sampled trees represent only survivors, inter-individual variability in iWUE was remarkably conserved over a century, suggesting that such a diversity may persist naturally within stands, even under environmental filtering. Early-life iWUE and diameter were both moderate predictors of cumulative adult growth in the low-density stand. No relationship was observed between early-life iWUE and cumulative adult growth in the high-density stand. In both sites, iWUE plasticity to drought was uninformative for explaining inter-individual differences in growth performance. Conclusion At best, early-life iWUE appeared a modest predictor of adult growth. However, this effect did not extend to tree survival or health.