Overyielding in experimental grassland communities - irrespective of species pool or spatial scale

In a large integrated biodiversity project ('The Jena Experiment' in Germany) we established two experiments, one with a pool of 60 plant species that ranged broadly from dominant to subordinate competitors on large 20 x 20 m and small 3.5 x 3.5 m plots (= main experiment), and one with a pool of nine potentially dominant species on small 3.5 x 3.5 m plots (= dominance experiment). We found identical positive species richness-aboveground productivity relationships in the main experiment at both scales. This result suggests that scaling up, at least over the short term, is appropriate in interpreting the implications of such experiments for larger-scale patterns. The species richness-productivity relationship was more pronounced in the experiment with dominant species (46.7 and 82.6% yield increase compared to mean monoculture, respectively). Additionally, transgressive overyielding occurred more frequently in the dominance experiment (67.7% of cases) than in the main experiment (23.4% of cases). Additive partitioning and relative yield total analyses showed that both complementarity and selection effects contributed to the positive net biodiversity effect.