Increasingly frequent severe drought events are pushing Mediterranean forests to unprecedented responses. Lack of management leads to dense forests that are highly susceptible to drought stress, potentially resulting in extensive dieback and increased vulnerability to other disturbances. Forest treatments like thinning and slash burning reduce competition for resources and have the potential to enhance tree growth and vigor and minimize tree vulnerability to drought. Here, we used tree rings to study the growth and physiological response of black pine (Pinus nigra) to drought in northeastern Spain under different treatments, including two thinning intensities (light and heavy, with 10% and 40% basal area reduction, respectively) followed by two understory treatments (clearing alone and in combination with slash burning), resulting in a research design of four treatments plus an untreated control with three replicates. Specifically, we studied basal area increment (BAI), resilience indices, and intrinsic water use efficiency (iWUE) using carbon and oxygen isotope composition (δ13C and δ18O in tree‐ring cellulose) before and after treatments. Our results showed that BAI and resistance to drought increased in the heavy‐thin (burned and unburned) and light‐thin burned units. Resilience increased in the burned units regardless of the thinning intensity, while recovery was not affected by treatment. Slash burning additionally increased BAI in the light‐thin and resistance and resilience in the heavy‐thin units compared with clearing alone. The stable isotope analysis revealed a minor effect of treatments on δ13C and δ18O. No change in iWUE among treatments was presumably linked to a proportional increase in both net CO2 assimilation and stomatal conductance, which particularly increased in the heavy‐thin (burned and unburned) and light‐thin burned units, indicating that these trees were the least affected by drought. This study shows that management approaches aimed at reducing wildfire hazard can also increase the vigor of dominant trees under drought stress. By reducing competition both from the overstory and the understory, thinning followed by clearing alone or in combination with slash burning promotes tree growth and vigor and increases its resistance and resilience to drought.

中文翻译：

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间伐和砍伐可以促进黑松的生长并降低其对干旱的脆弱性


日益频繁的严重干旱事件正促使地中海森林做出前所未有的反应。缺乏管理导致森林茂密，极易受到干旱胁迫，可能导致大面积枯死，并增加对其他干扰的脆弱性。间伐和砍伐等森林处理减少了对资源的竞争，并有可能增强树木的生长和活力，并最大限度地减少树木对干旱的脆弱性。在这里，我们利用树木年轮研究了西班牙东北部黑松 (Pinus nigra) 在不同处理下对干旱的生长和生理反应，包括两种间伐强度（轻度和重度，分别减少 10% 和 40% 的断面积减少）随后进行两次林下处理（单独清理和与砍伐结合），从而形成了四种处理的研究设计以及具有三个重复的未经处理的对照。具体来说，我们使用处理前后的碳和氧同位素组成（树轮纤维素中的δ13C和δ18O）研究了断面积增量（BAI）、恢复力指数和内在水分利用效率（iWUE）。我们的结果表明，重度薄度（燃烧和未燃烧）和轻度薄度燃烧单位的 BAI 和抗旱能力有所增强。无论间伐强度如何，烧伤单位的恢复力都会增加，而恢复则不受治疗的影响。与单独清理相比，砍伐燃烧还增加了轻薄单位的 BAI 以及重薄单位的抵抗力和弹性。稳定同位素分析显示处理对 δ13C 和 δ18O 的影响较小。 处理间 iWUE 没有变化可能与净二氧化碳同化和气孔导度的成比例增加有关，尤其是在重度稀疏（燃烧和未燃烧）和轻度稀疏燃烧单位中增加，表明这些树木受到的影响最小因干旱。这项研究表明，旨在减少野火危害的管理方法也可以增加干旱胁迫下优势树木的活力。通过减少林上和林下的竞争，间伐后单独清理或与砍伐结合起来，可以促进树木生长和活力，并提高其对干旱的抵抗力和恢复力。