Plant community composition and dominant species drive stability in aboveground production of biofuel agroecosystems

Abstract

The relationship between diversity and stability remains a key question in ecology and has important consequences for understanding the sustainability (and profitability) of bioenergy cropping systems; yet to date, little work has been done to examine these relationships in agricultural systems directly. In this study, we evaluated the relationship between biodiversity (in number of planted species) and the stability of biomass production in four experimental bioenergy cropping systems established in Wisconsin and Michigan. Species composition and aboveground production were monitored at all sites for 8–10 years (2010–2019) allowing us to evaluate the temporal stability of biomass yield (defined as the temporal mean divided by the temporal SD) in these cropping systems. A major regional drought in 2012 also allowed us to evaluate resistance and resilience. Although three of the cropping systems were established with the same seed mixtures and were managed in the same way, species composition differed markedly between sites. This limited our ability to attribute differences within cropping systems across sites to the abundance of specific species. Overall, there was no clear relationship between planted species richness and yield stability in biomass production at these sites. At both sites, the lowest diversity system (switchgrass monoculture) had the highest interannual stability in production and was equivalent to that of the highest diversity treatment (prairie). Resilience to the drought was high in all treatments and did not differ among the four cropping systems; however, resistance to drought differed among systems and was highest in the switchgrass monocultures at both sites. The abundance of perennial C4 grasses increased over time in all cropping systems, except for the successional plots. The persistence of annual species in the successional treatments at both sites likely contributed to low stability and high interannual turnover in this system. We found no evidence that increasing the diversity of planted species in bioenergy cropping systems enhances stability in aboveground biomass production; nor was there any difference in resistance or resilience to drought. The higher costs of establishing more diverse bioenergy cropping systems may be warranted if other ecosystem services, such as supporting diverse pollinator and predator insect species at the landscape scale, are desired from bioenergy crops in addition to biomass production.