Contrasting effects of bioenergy cropping systems on arthropod biodiversity

Bioenergy cropping could transform landscapes in coming decades and have sweeping impacts on biodiversity. The nature of these changes is uncertain and will depend on which crops are adopted, how they are managed, and which types of ecosystems they replace. We censused several arthropod groups in a long-term experimental array in southwest Michigan, US, containing ten replicated bioenergy cropping systems. The cropping systems spanned a gradient including intensive annual crops (corn, two sorghum systems), simple perennial systems (Miscanthus, two switchgrass systems, and a native grass mix), and complex perennial polycultures (reconstructed prairie, successional vegetation, and short-rotation poplar).

For most groups we censused, species richness was very low in annual systems, slightly higher in simple perennial systems (dominated by one or a few grass species), and dramatically higher in complex perennial systems (reconstructed prairie, successional vegetation, and poplar). This pattern was very strong for bees, butterflies, and ants, but not ground beetles. Cropping systems we censused formed a plant species richness gradient which was a strong positive predictor of richness for all arthropod groups except ground beetles. Our findings illustrate the widely contrasting biodiversity outcomes that bioenergy adoption could bring about. Responding to energy demands by expanding annual cropping systems or converting natural habitats to simple perennial systems will have strongly adverse effects for biodiversity; in contrast, replacing marginal annual crops with diverse perennial bioenergy systems could greatly enhance biodiversity in simplified agricultural landscapes.