Data from: Positive effects of tree species diversity on productivity switch to negative after severe drought mortality in a temperate forest experiment

Synthesis of a large body of evidence from field experiments suggests more
diverse plant communities are both more productive as well as more
resistant to the effects of climatic extremes like drought. However, this
view is strongly based on data from grasslands due to limited empirical
evidence from tree diversity experiments. Here we report on the
relationship between tree diversity and productivity over ten years in a
field experiment established in 2005 that was then affected by the 2018
megadrought in central Europe. Across a number of years, tree species
diversity and productivity were significantly positively related, however,
the slope switched to negative in the year of the drought. Net diversity
effects increased through time, with complementarity making greater
continuations to the net diversity effect than selection effects.
Complementarity was clearly positive (95 % credible interval) in three and
five species mixtures before the drought (2012-2016) but was found to
decrease in the year of the drought. Selection effects were clearly
positive in 2016, and remained positive in 2018, the drought year in two,
three, and five species mixtures. Survival of the Norway spruce (Picea
abies) plummeted during drought and a negative relationship between
species diversity and spruce survival was found. Our findings suggest that
tree diversity per se may not buffer communities against the impacts of
extreme drought and that tree species composition and the drought
tolerance of tree species (i.e., species identity) will be important
determinants of community productivity as the prevalence of drought
increases.

基于野外实验获取的大量证据表明，物种更丰富的植物群落不仅生产力更高，同时对干旱等气候极端事件的抗性也更强。然而，由于树木多样性实验的实证数据较为匮乏，这一观点主要基于草原生态系统的观测结果。本研究针对2005年建立的野外实验样地展开了长达十年的追踪，该样地曾受2018年欧洲中部特大干旱影响。研究期内多数年份中，树木物种多样性与生产力呈显著正相关关系，但在干旱发生当年，二者的相关斜率转为负值。净多样性效应随时间推移逐渐增强，其中互补效应对净多样性效应的贡献大于选择效应。在干旱发生前的2012-2016年，3种和5种树木混播群落的互补效应显著为正（95%可信区间），但在干旱当年，互补效应出现下降。2016年选择效应显著为正，在干旱发生的2018年，2种、3种及5种混播群落的选择效应仍保持正值。欧洲云杉（Picea abies）的存活率在干旱期间骤降，且物种多样性与云杉存活率呈负相关关系。本研究结果显示，树木物种多样性本身或许无法缓冲群落面临的极端干旱冲击，而随着干旱事件频发，树木物种组成以及树种的耐旱性（即物种特性）将成为决定群落生产力的关键因素。