Flower-power in the bioenergy sector – A review on second generation biofuel from perennial wild plant mixtures

The cultivation of perennial wild plant mixtures (WPMs) for biogas production promises to be a good complement to monotonous biogas cropping systems dominated by maize (Zea mays L.). WPMs offer not only biomass for power, heat, and second generation biofuel, but also a wide variety of wild plant species, a diverse range of food and habitats for wildlife, erosion mitigation and much more. This makes WPM cultivation more social-ecologically promising than conventional, mostly annual biogas cropping systems. Here, the scientific background of the suitability of WPM cultivation is examined in a literature review and through interviews with experts. It was found that WPM cultivation can only be considered a useful new cultivation system under certain conditions. Marginal agricultural lands and strip cultivation on favorable land appear to be promising approaches. However, there are considerable risks associated with WPM cultivation such as weed infestation or poor establishment of the plant species, both of which would be unacceptable on a larger scale. Low methane yield level could aggravate land use conflicts in the future. It thus makes sense to integrate WPM cultivation into existing agricultural systems with a special focus on enhanced ecosystem services, other than biomass supply, such as habitat functioning, soil protection and landscape improvement. Key research topics for WPM-related projects would therefore include not only the optimization of the establishment procedure and the improvement of the species composition for different types of marginal agricultural land but also the assessment of optimal strategies for integrating WPM cultivation into existing agroecosystems.