Can the results of biodiversity-ecosystem productivity studies be translated to bioenergy production?
Biodiversity experiments have suggested that increases in plant diversity can lead to greater biomass production, and some researchers suggest high diversity plantings should be used for bioenergy production. However, the methods used in biodiversity experiments may limit their economic feasibility for bioenergy plantings. For example, intensive management such as hand weeding to maintain low diversity plantings and exclude unplanted species would not be done in production scale plantings. Also, biodiversity experiments generally use high seeding densities that would be cost prohibitive in commercial plantings (over $10,000 of seed per acre). We set out to create more economically realistic diverse plantings in two field studies in southern Michigan, USA. One study involved comparing production between switchgrass (Panicum virgatum) and prairie plantings on private farm fields that were managed similarly to bioenergy plantings and sown with representative seed mixes. The other study was an experiment in which switchgrass was sown in monoculture and in combination with native prairie species into increasingly species rich mixtures.
Our results show that bioenergy plantings with higher species richness did not produce greater biomass than switchgrass monocultures. The lack of a positive relationship between planted species richness and production in our studies may be due to invasion and establishment of non-planted species that were not removed. Alternately, we discovered during our analyses that low seeding density may have limited the establishment of potentially high productivity species. Production in high diversity bioenergy plantings may be increased by using a high density of switchgrass and other potentially highly productive species that have inexpensive seed, and future efforts to translate the results of biodiversity experiments to bioenergy plantings should especially consider the role of seeding density.