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 decreas..., , , # Positive effects of tree species diversity on productivity switch to negative after severe drought mortality in a temperate forest experiment [https://doi.org/10.5061/dryad.vt4b8gv08](https://doi.org/10.5061/dryad.vt4b8gv08) The Kreinitz experiment site is located near the village of Kreinitz-Zeithain, Saxony, Germany (51°23’ 08” N, 13°15’41” E; 115 m a.s.l.). The local climate is characterized by a mean annual precipitation of 578 mm and mean annual temperature of 9.4 °C (30-year average 1981-2010, Oschatz station of German Weather Service DWD, ~15 km from the site). Maximum precipitation is normally observed during the growing season (Table S1), which usually starts in late March and ends in late October / early November (Scheuner, 2004). The soil is a humic cambisol on a bedrock of sand and gravel (93 % sand, 6 % silt, 1 % clay) with a pH of 5.5 (Schwarz et al., 2015). Kreinitz was planted in a field that was cultivated until 1990. In summer 2005, the site was plowed and harrow...综合多项野外实验的大量证据表明，植物群落多样性越高，其生产力越强，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证据较为匮乏，这一观点主要基于草地生态系统的研究数据。本研究针对2005年建立的野外实验站展开了长达十年的树木多样性与生产力关系分析，该实验站曾受2018年中欧特大干旱影响。 多年观测结果显示，树木物种多样性与生产力呈显著正相关，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不断增强，其中互补效应对净多样性效应的贡献大于选择效应。干旱发生前（2012-2016年），3种和5种树木的混交群落中，互补效应显著为正（95%可信区间），但研究发现其呈下降趋势…… # 温带森林实验中树木物种多样性对生产力的正向效应在严重干旱导致树木死亡后转为负向 [https://doi.org/10.5061/dryad.vt4b8gv08] 克莱尼茨（Kreinitz）实验样地位于德国萨克森州克莱尼茨-蔡泰恩（Kreinitz-Zeithain）村附近（北纬51°23′08″，东经13°15′41″；海拔115米）。当地气候以年均降水量578毫米、年均气温9.4℃为特征（1981-2010年30年平均值，数据来源于距样地约15公里的德国气象局（DWD）奥沙茨站点）。降水峰值通常出现在生长季（表S1），生长季一般始于3月下旬，止于10月下旬/11月初（Scheuner, 2004）。该样地土壤为砂和砾石母质上发育的腐殖质雏形土（humic cambisol），砂粒占比93%、粉粒6%、黏粒1%，pH值为5.5（Schwarz等, 2015）。 克莱尼茨实验样地所在地块此前一直被耕作至1990年。2005年夏季，该站点被翻耕并耙地……