Can the Results of Biodiversity-Ecosystem Productivity Studies Be Translated to Bioenergy Production?

Abstract

Biodiversity experiments show that increases in plant diversity can lead to greater biomass production, and some researchers suggest that high diversity plantings should be used for bioenergy production. However, many methods used in past biodiversity experiments are impractical for bioenergy plantings. For example, biodiversity experiments often use intensive management such as hand weeding to maintain low diversity plantings and exclude unplanted species, but this would not be done for bioenergy plantings. Also, biodiversity experiments generally use high seeding densities that would be too expensive for bioenergy plantings. Here we report the effects of biodiversity on biomass production from two studies of more realistic bioenergy crop plantings in southern Michigan, USA. One study involved comparing production between switchgrass (Panicum virgatum) monocultures and species-rich prairie plantings on private farm fields that were managed similarly to bioenergy plantings. The other study was an experiment where switchgrass was planted in monoculture and in combination with increasingly species-rich native prairie mixtures. Overall, we found that bioenergy plantings with higher species richness did not produce more biomass than switchgrass monocultures. The lack of a positive relationship between planted species richness and production in our studies may be due to several factors. Non-planted species (weeds) were not removed from our studies and these non-planted species may have competed with planted species and also prevented realized species richness from equaling planted species richness. Also, we found that low seeding density of individual species limited the biomass production of these individual species. Production in future bioenergy plantings with high species richness may be increased by using a high density of inexpensive seed from switchgrass and other highly productive species, and future efforts to translate the results of biodiversity experiments to bioenergy plantings should consider the role of seeding density.

Perennial biomass crop establishment, community characteristics, and productivity in the upper US Midwest: Effects of cropping systems seed mixtures and biochar applications

“…In contrast to some plant research (Hector et al, 1999;Tilman et al, 2001), the HD cropping system plots in the current experiment did not outperform the less diverse cropping systems (SG and LD). As discussed by Dickson and Gross (2015) and Von Cossel and Lewandowski (2016), realistic seeding rates and challenges in weed control can obscure the purported benefits of diverse plantings, especially during the establishment period. In our experiment, while the switchgrass (SG) monocultures experienced a poor initial establishment year, resown plots exceeded sown biomass production in LD and HD plots within three seasons of the initial planting date.…”

“…Increasing seeded plant diversity may help alleviate weed pressure and reduce erosion during the establishment period through rapid ground cover by desirable species (Tilman, 1997;Fargione and Tilman, 2005;Bonin et al, 2014). Others point out that higher plant diversity may reduce ethanol yields (Adler et al, 2009), that plant diversity may decline over time and yields remain unstable (Von Cossel and Lewandowski, 2016), and that ecosystem benefits observed in smallplot diversity experiments may not hold true in large-scale biomass crop plantations (Dickson and Gross, 2015). One potential solution to address these concerns is establishment of a moderately diverse mixture of high-yielding plant species that balances the benefits and challenges of both monocultures and highly diverse plant mixtures (DeHaan et al, 2010;Bonin and Tracy, 2012).…”

Cellulosic biofuel contributions to a sustainable energy future: Choices and outcomes

“…However, many years may be required to fully realize any productivity benefits resulting from diversity. Tilman et al (34) documented increased productivity after 10 years, and Gelfand et al (24) recorded a 50% jump in the productivity of their mixed-species successional community after an initial 10-year establishment period because of the delayed dominance of high-productivity species (37). Two exceptions to the disadvantage of annual biofuel crops prove instructive.…”

Transferring biodiversity-ecosystem function research to the management of ‘real-world’ ecosystems

“…Studies have also shown that diverse grassland mixtures produce greater bioenergy yields (Khalsa et al, 2014;Tilman et al, 2006). However, another study of bioenergy production in grass mixtures showed that diverse mixtures were not more productive than currently used monocultures, thus showing that diversification might not always promote bioenergy production (Dickson and Gross, 2015). Even in the absence of positive impacts of diversity on productivity, other benefits may be realized; diverse bioenergy landscapes can promote the supply of other ecosystem services including greenhouse gas mitigation, pest suppression, pollination, and bird watching potential (Werling et al, 2014).…”