|One of our experimental sites with a clear checkerboard pattern illustrating the different plant communities that varied in richness (monocultures, 4-species mixtures) and evenness (relative abundance of the four species).|
In principle, there are competing processes that result in the answer to this question being not so clear. The best of the component monocultures is obviously best-suited to the prevailing conditions. The mixture of different species offers the possibility of synergistic (and antagonistic) interspecific interactions that may positively (or negatively) affect yield. However, any synergistic effects have to be sufficiently advantageous to overcome the effect of diluting the yield of the highest-yielding monoculture species with that from lower-yielding species.
As part of EU COST Action 852 ‘Quality legume-based forage systems for contrasting environments’, we established a common diversity experiment that involved monocultures of four agronomic species (two grasses and two legumes) and a range of 4-species agronomic communities at each of 30 European sites and a Canadian site. A common field experiment of 30 plots was established at each site with two seed density levels of a design with four monocultures (single species) and 11 mixtures (with systematically varying proportions of four species).
Answer: Definitely! Overyielding occurs when a mixture (open circles in Fig. 1 represent each of the 11 mixture communities at a site) performs better than the average monoculture performance (shaded square in Fig. 1). Note that each data point averages across years, and across the two seeding densities.
|Fig. 1. Mixtures generally yielded better than the best-performing monoculture across the 31 international field sites. Average annual yield (includes weed biomass) of 11 mixture communities that varied in their sown relative abundances (○), the maximum-yielding monoculture (▬) and mean monoculture yield (■) at each site. Sites arranged in order of biomass production. Symbols above sites indicate where mixtures significantly outyielded the best-performing monoculture. From Finn et al. (2013).|
Kirwan, L., Lüscher, A., Sebastià, M.T., Finn, J.A., Collins, R., Porqueddu, C., Helgadóttir, A., Brophy, C., Bélanger, G., Fothergill, M., Frankow-Lindberg, B., Garcia-Sarrion, R., Ghesquiere, A., Golinski, P., Jørgensen, M., Kadžiuliene, Z., Nyfeler, D., Nykänen-Kurki, P., Parente, G., Vasileva V. and Connolly, J. 2007. Evenness drives consistent diversity effects in intensive grassland systems across 28 European sites. Journal of Ecology 95: 530-539. See related post.