At two sites (Zürich, Switzerland and Wexford, Ireland) we evaluated the efects of experimentally imposed summer drought on intensively managed grassland communities (3×5 m plots) of varying richness (1 and 4 species), and comprising four species (Lolium perenne L., Cichorium intybus L., Trifolium repens L., Trifolium pratense L.). he short-term drought efects in the individual growth period resulted in strong yield reductions of -39 and -85% in the average across monocultures at Zürich and Wexford, respectively. However, during the same period, the yield advantage from mixing species could compensate for this drought impairment at Zürich. In the three combined harvests across the drought and post-drought period and under control and drought conditions, mean yields were higher (P<0.05), and yield variance was lower (P<0.05) in four-species communities than in monocultures, indicating that yield stability was enhanced in four-species mixtures. he total annual yield (across all harvests) of mixtures under drought exceeded the average annual yield of the rain-fed monocultures. he beneit due to mixtures (~33% increase in annual yield, P<0.05, across sites) was substantially greater than the weak impact of drought (-5% reduction in annual yield, across sites). hese results illustrate the high potential for multi-species mixtures to compensate for drought-induced yield losses from the scale of individual harvests to the whole year.
