Promoting tree species diversity is commonly advocated in the anticipation of predicted increases in drought frequency and severity. However, mixing effects on drought responses vary substantially with site conditions and species identity. We combined annually resolved tree-ring data and repeated forest inventory data spanning the last 90 years to examine the effect of species-specific neighbourhood competition on the drought response (resistance, recovery and resilience) of European beech (Fagus sylvatica), silver fir (Abies alba) and Norway spruce (Picea abies) for six drought events that occurred since the 1970s at three sites in Switzerland. We found predominantly weak neighbourhood competition and tree species diversity effects, with significant interspecific influences only for resistance and recovery of beech. These minor neighbourhood effects were outweighed by tree age and size effects. Although age effects depended on species identity and components of resilience, tree size consistently negatively affected all species. Our results emphasize that diversity effects may vary for each given species combination which makes broader conclusions challenging. This is because species interact through their specific set of traits and interactions vary in space and time. Adaptive management strategies are likely to be more effective when they promote more drought-tolerant species and reductions in stand density. Despite the absence of an unequivocal advantage of tree diversity on drought resilience, striving towards species-rich forests nonetheless allows for a risk spreading among multiple species and the reinforced provision of numerous ecosystem services.

在预期干旱频率和严重程度将增加的预测中，通常提倡树种多样性。但是，对干旱反应的混合影响随地点条件和物种身份的不同而有很大差异。我们结合了过去90年的年分解树木年轮数据和重复的森林清单数据，以研究特定物种的邻域竞争对欧洲山毛榉（Fagus sylvatica），银杉（冷杉（Abies alba）和挪威云杉（Picea abies）），这是自1970年代以来在瑞士三个地点发生的六次干旱事件。我们发现主要是弱的邻里竞争和树木物种多样性效应，仅对山毛榉的抗性和恢复具有重要的种间影响。这些较小的邻里效应被树木年龄和大小效应所抵消。尽管年龄的影响取决于物种的身份和复原力的组成部分，但树木的大小始终对所有物种产生负面影响。我们的结果强调，对于每种给定的物种组合，多样性效应可能会有所不同，这使得更广泛的结论具有挑战性。这是因为物种通过其特定的特征集相互作用，并且相互作用在空间和时间上有所不同。当适应性管理策略促进更多的耐旱物种和降低林分密度时，它们可能会更有效。尽管缺乏树木多样性在抗旱性方面的明确优势，但努力发展物种丰富的森林仍使风险分散在多种物种之间，并加强了提供多种生态系统服务的风险。