Herbaceous Perennials: Placement, benefits and incorporation challenges in diversified landscapes

Herbaceous perennial feedstocks will fill numerous and critical roles in the bioenergy landscape. Our objective is to present the benefits and challenges of growing herbaceous perennials and provide regionally-specific scenarios for their use at the landscape scale. The primary herbaceous perennial feedstocks will vary by agro-ecoregion and will include switchgrass, Miscanthus, alfalfa, native polycultures, sugar cane, and energy cane. In the near term, optimizing sustainable yield will drive the economic feasibility of herbaceous perennials. However, within agro-ecoregions, feedstock selection will be site-specific based on landscape position, potential ecosystem services, and producer-driven acceptance such as economics, familiarity, and committing land to long-term feedstock production. For example, in the central and northern Great Plains, managed switchgrass monocultures produce three times more dry matter and provide fewer establishment and management challenges than extensively managed native polycultures. Since yield is of paramount importance, native polycultures may be suited only to situations where ecosystem restoration and increased plant species diversity are primary objectives. In the Midwest, Miscanthus x giganteus produces more biomass with fewer inputs than other herbaceous perennials, though the cost of establishment and time required to keep stands in production to offset the cost of establishment may limit producer acceptance on a large scale until non-invasive, seeded varieties can be developed. In the Gulf Coast states, sugar cane has been in production for more than 200 years, so expanding production for bioenergy provides fewer barriers. The Southeast has the most diverse selection of herbaceous biomass crops which will be determined by local growing conditions, available harvest technology, and environmental considerations. Challenges in the Southeast include reluctance to adopt novel crops and the predominance of degraded soils on sites available for cultivation. Balancing biomass production, ecosystem services and producer acceptance will be major challenges for a diversified landscape in the new bioeconomy.