Summary of mixed effects models for aboveground biomass in August 2009 and 2010 as well as for decomposed wheat litter.

For the analysis we used all plots of the Jena experiment, except for the 60-species mixtures. In Model A the treatment contrast was split into a contrast for roofed versus unroofed subplots (DRvsU), which aggregates the drought (D) and roofed control (R) treatments and tested it against the unroofed (U) treatment, and the residual contrast (DvsR), which considers the pure drought effect. In Model B the treatment contrast was split in a contrast of dry versus wet subplots (DvsRU), which aggregates the unroofed and roofed control treatments and tested it against the drought treatment, and the residual contrast (RvsU), which considers the roof artifact effects. Df = degrees of freedom; Num = numerator; Den = Denominator.