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...