Understanding the impact of management upon post-drought tree growth recovery and drought legacy effects is among the fundamental challenges hindering the improvement of forest conservation strategies in the face of increasingly frequent, longer, and intensified extreme droughts under ongoing climate change. Yet surprisingly little is known to date about how management practices can influence drought legacy effects; and previous studies of management impacts on forest resilience to drought have reached inconsistent and contentious conclusions. This study sought to tackle these pressing questions and gain insight by analyzing tree-ring datasets from non-managed and managed Qinghai spruce forests in northwestern China. The results show improved growth resilience to drought of those trees under management practices. Moreover, Qinghai spruce radial growth in non-managed forest exhibited significant legacy effects of extreme drought, whereas such legacy effects were mitigated in managed forest. Nevertheless, both the resilience augmentation and the mitigation of drought legacy effects by management were much weaker in the face of a three-year persistent drought than a single-year event. Hence, we may conclude that current management practices are advantageous and necessary for forest conservation under exacerbated drought conditions, for which strategies and measures should be better thought out and tailored to specific situations, rather than being one-size-fits-all, to better serve the goals of forest managers and conservationists.

Understanding varying climate responses in tree-ring data across tree ages is important, but little is known about tree-age effects on climate responses in tree-ring stable isotopes. To detect whether age differences in tree-ring delta C-13 and delta O-18 could lead to differing climate responses, we measured tree-ring cellulose delta C-13 and delta O-18 (1901-2010) from Schrenk spruce (Picea schrenkiana) trees in northwestern China with ages ranging from 110 to 470 years, which we binned into three age groups. Tree-ring delta C-13 (pin-corrected) and delta O-18 exhibited similar year-to-year variability between age groups and did not feature age-related trends. delta C-13 series from old trees (270-470 years) showed stronger legacy effects, reflecting influences from the antecedent period (due to carbohydrate reserves and climate), compared to young trees (110-125 years). Both tree-ring delta C-13 and delta O-18 values decreased with increasing relative humidity (RH) and precipitation and with decreasing mean and maximum temperatures during the main growing season (May-August). delta C-13 and delta O-18 exhibited age-dependent climate responses: Young trees had a stronger climate response in delta C-13 but a weaker or similar climate response in delta O-18 compared to old trees. We developed multiple growing-season RH reconstructions based on composite chronologies using delta C-13 and delta O-18 series from different age groups. In particular, we found that including delta C-13 from young trees improved the skill of RH reconstructions because of the age-specific mechanisms driving the delta C-13-climate relationship, but that caution is warranted with regard to extreme values. We therefore suggest that young trees should be considered when using stable isotopes, particularly in delta C-13, for climate reconstruction.