Key message

Under severe drought, growth of Norway spruce suffered much more than European beech. Norway spruce benefited from growing in the environment of beech, and both species acclimated slightly to 5 years of experimentally extended drought.

Abstract

Recent studies show that the detrimental effects of drought on stand growth are mitigated when the stand contains mixed tree species. We analysed the growth responses of Norway spruce and European beech to episodic and experimentally extended drought in intra- and inter-specific mature stands. We used annual diameter growth records dating back to 1998 to determine the impact of the natural episodic drought in 2003 and 2015. To analyse extended drought, spruce and beech trees were exposed to extreme drought under automatic throughfall exclusion roofs from 2014 to 2018. The growth of spruce in an inter-specific environment with beech was 20–50% less affected by natural episodic drought compared with an intra-specific constellation. When beech grew in an inter-specific environment, it was by 23% more affected by drought compared to intra-specific conditions, but seemed to recover faster. The induced drought from 2014 to 2018 resulted in a strong growth reduction in the first year particularly for spruce, followed by a slight acclimation to the dry conditions. Beech acclimated and recovered faster than spruce across all growing conditions, while spruce only acclimatized faster in the environment of beech. Both species showed a higher mortality under induced drought compared with the controls; for spruce, the mortality rate was fivefold higher compared to the long-term mortality. The long-term moderate-growth stabilization and the growth increase after the 5-year exposure to drought suggest a gradual acclimation to drought by beech. The resistance and acclimation to drought of spruce when growing in mixture should be considered when designing resource efficient and productive mixed conifer-broadleaved stands for future climates.

中文翻译：

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挪威云杉和欧洲山毛榉在单物种和混合物种中的生长和死亡率都处于自然发作和实验性干旱的条件下。KROOF穿透瀑布排除实验的结果

关键信息

在严重干旱下，挪威云杉的生长遭受的危害要远远大于欧洲山毛榉。挪威云杉得益于山毛榉环境中的生长，并且两个物种在实验性干旱下均能适应5年的干旱。

抽象

最近的研究表明，当林分中混有树木时，干旱对林分生长的不利影响就会减轻。我们分析了挪威云杉和欧洲山毛榉对种内和种间成熟林分干旱和实验性干旱的生长响应。我们使用1998年以来的年度直径增长记录来确定2003年和2015年自然发作性干旱的影响。为了分析长期干旱，从2014年至2018年，云杉和山毛榉树在自动防穿透屋顶下遭受了极端干旱。与种内星座相比，在山毛榉种间环境中的云杉受自然突发干旱的影响要少20–50％。当山毛榉在特定环境中生长时，与种内条件相比，受干旱影响的比例要高23％，但恢复速度似乎更快。2014年至2018年的干旱导致第一年的生长大幅下降，尤其是云杉，其后略微适应干旱条件。在所有生长条件下，山毛榉的适应和恢复速度都比云杉快，而云杉仅在山毛榉的环境中适应得更快。与对照相比，这两种物种在诱导干旱下均表现出较高的死亡率；对于云杉，死亡率比长期死亡率高五倍。长期处于中等水平的稳定化以及在遭受干旱5年后的增长增加表明山毛榉逐渐适应了干旱。