Forests worldwide face increasingly frequent, prolonged, and severe droughts driven by climate change, causing widespread tree dieback and productivity losses. Yet predicting how trees recover water-carbon balance and growth after non-lethal drought remains challenging. To address this, we subjected juvenile Pinus radiata D. Don - a drought-tolerant, strongly isohydric conifer - to moderate (14 weeks) and extended (20 weeks) dry-down periods. We continuously monitored stem radial growth and water reserves for over six months with high-resolution dendrometers, alongside weekly measurements of leaf gas exchange, capturing fine-scale dynamics of water-carbon balance and growth during stress and recovery. We recorded a complete recovery of leaf function and stem growth in all plants after drought release, but recovery rate depended on drought duration: plants under prolonged stress recovered more slowly. Stomatal conductance returned to control levels after c. 1. 5 and 2. 5 weeks following moderate and extended drought, respectively, whereas net CO₂ assimilation recovered within c. 1. 5 weeks regardless of drought duration. In contrast, cambial activity resumed rapidly, within a few days up to a week, as soon as stem water reserves were refilled. Growth recovery was rapid even in plants that experienced very low water potentials and nearly two months in a neutral or negative carbon balance state. Wood formation resumed ahead of photosynthesis recovery, reflecting a decoupling between carbon source and sink processes. Although drought reduced total radial growth, aboveground biomass gain in stressed plants remained comparable to that of well-watered controls, even for those with a growing period halved because of drought. This high degree of growth resilience arose through compensatory growth, with post-stress growth rates 1. 4-2. 4 times higher than pre-stress rates. These findings provide new insights into drought response and recovery in a conifer with conservative water regulation and will improve model predictions of juvenile-tree resilience under future climates.
Firm et al. (Thu,) studied this question.