Abstract Drought-induced dieback episodes are globally reported among forest ecosystems but they have been understudied in scrublands. Chronically-stressed individuals are supposed to be more vulnerable prior to drought which triggers death. We analyzed drought-triggered dieback and mortality events affecting Mediterranean Juniperus phoenicea scrublands in two sites with contrasting climate and soil conditions located in Spain. We characterized the radial growth patterns of coexisting living and dead junipers, including the calculation of growth statistics used as early-warning signals, quantified growth response to climate, and analyzed the wood C and O isotope discrimination. In the inland, continental site with rocky substrates (Yaso), dead junipers grew less than living junipers about three decades prior to the dieback started in 2016. However, in the coastal, mild site with sandy soils (Donana), dead junipers were smaller but grew more than living junipers about two decades before the dieback onset in 2005. The only common patterns between sites were the higher growth coherence in both living and dead junipers prior to the dieback, and the decrease in growth persistence of dead junipers. Cool and wet conditions in the prior winter and current spring, and cool summer conditions enhanced juniper growth. In Donana, growth of living individuals was more reduced by warm July conditions than in the case of dead individuals. Higher δ13C values in Yaso indicate also more pronounced drought stress. In Yaso, dead junipers presented lower δ18O values, but the opposite occurred in Donana suggesting different changes in stomatal conductance prior to death. Warm summer conditions enhance evapotranspiration rates and trigger dieback in this shallow-rooted species, particularly in sites with a poor water-holding capacity. Chronic, slow growth is not always a reliable predictor of drought-triggered mortality.

中文翻译：

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干旱引起的杜松枯死和死亡：灌木死亡前的不同生长和木材同位素模式

摘要 干旱引起的枯死事件在全球森林生态系统中都有报道，但在灌木丛中却没有得到充分研究。在引发死亡的干旱之前，长期承受压力的人应该更容易受到伤害。我们分析了在西班牙气候和土壤条件截然不同的两个地点影响地中海杜松灌木丛的干旱引发的枯死和死亡事件。我们描述了共存的活杜松和死杜松的径向生长模式，包括计算用作预警信号的生长统计数据、量化生长对气候的响应，并分析了木材 C 和 O 同位素的鉴别。在 2016 年开始枯死前大约 30 年，在内陆、具有岩石基质的大陆站点 (Yaso)，死桧树的生长速度低于活桧树。 然而，在沿海、沙质土壤的温和地点 (Donana)，在 2005 年枯萎开始前大约 20 年，死的杜松较小，但比活的杜松长得更多。 地点之间唯一的共同模式是活杜松和死杜松的生长一致性更高在枯死之前，以及死亡杜松的生长持久性下降。前冬和今春凉爽潮湿的条件以及凉爽的夏季条件促进了杜松的生长。在多纳纳，与死亡个体相比，7 月温暖的气候条件对活体个体的生长抑制得更多。Yaso 较高的 δ13C 值也表明干旱胁迫更为明显。在 Yaso，死亡的杜松呈现较低的 δ18O 值，但在 Donana 发生相反的情况，表明死亡前气孔导度发生了不同的变化。温暖的夏季条件会提高蒸发蒸腾率并引发这种浅根物种的枯死，特别是在持水能力差的地方。慢性、缓慢的增长并不总是干旱引发的死亡率的可靠预测指标。