Investigating the effects of production-scale harvesting on pollination and biocontrol services in bioenergy grasslands
Conversion of marginal agricultural lands to perennial crops for bioenergy production in the Midwestern United States has the potential to help sustainably meet energy needs without sacrificing food production. It has become clear that perennial grasslands can contain a greater diversity of pollinator and natural enemy species than annual bioenergy crops, such as corn, and that this diversity translates to greater pollination and pest suppression services. However, we know very little about how the disturbance caused by the production-scale harvesting of grasslands for bioenergy will affect biodiversity and ecosystem services. We therefore conducted multi-year experiment to determine (1) how the production-scale harvest of perennial grasslands affects pollinator and natural enemy diversity and the ecosystem services they provide, and (2) whether harvesting effects vary with landscape context. We sampled pollinator and natural enemy diversity, pollinator visitation rates, and natural enemy predation rates in 18 Wisconsin grasslands (9 harvested and 9 left unharvested). We report some of our preliminary findings after the first year of our experiment.
After one year, we found that production-scale grassland harvesting had little effect on pollinator diversity or pollinator visitation rates. However, harvesting did have an effect on some natural enemy groups. For example, ant abundance was greater in harvested sites, which may explain the greater predation rates on sentinel arthropod eggs. Landscape context had effects on pollinators and natural enemies, but for some natural enemy groups, landscape context effects were stronger in harvested grasslands. Our results suggest that perennial grassland harvesting for bioenergy production can have some immediate positive effects on natural enemy diversity and biocontrol services but the longer-term effects after multiple years of harvest are yet to be determined.