Age-Dependent Demographic Rates of the Bioenergy Crop Miscanthus × giganteus in Illinois

Abstract Some plants being considered as bioenergy crops share traits with invasive species and have histories of spreading outside of their native ranges, highlighting the importance of evaluating the invasive potential before the establishment of large-scale plantings. The Asian grass Miscanthus × giganteus is currently being planted as a bioenergy crop in the north central region of the United States. Our goal was to understand the demographic rates and vegetative spread of this species in unmanaged arable lands in Illinois to compare with those of large-statured invasive grasses (LSIGs). We collected data from 13 M. × giganteus plantings in Illinois, ranging in age from 1 to 7 yr, recording tiller number, plant spatial extent, spikelet production, and plant survival over 4 yr. Additionally, to understand recruitment potential, we conducted a greenhouse germination experiment, and, to estimate establishment from rhizome fragments, field trials were performed. Miscanthus × giganteus demographic rates were age dependent. Spikelet production was high, with 1- and 4-yr plants producing an annual average of more than 10,000 and 180,000 spikelets plant−1, respectively; however, data from our germination trial suggested that none of these spikelets had the potential to yield seedlings. On average, plants expanded vegetatively 0.15 m yr−1. Tiller density within the center of a clone decreased with age, possibly leading to a “dead center” found among some LSIGs. Rhizome establishment increased with weight, ranging from 0 to 42%. Survival was low, 24%, for first-year plants but quickly climbed to an asymptote of 98% survival for 4-yr-old plants. Our results suggest that efforts should be made to eradicate plants that escape biomass production fields within a year of establishment, before the onset of high survival. Future work is needed to determine what types of natural and anthropogenic disturbances can fragment rhizomes, leading to regeneration. Nomenclature: Miscanthus × giganteus Greef et Deu ex Hodkinson et Renvoize, Giant miscanthus. Management Implications: As demand for alternative fuels continues to grow, biofuels from herbaceous perennial biomass crops will be an important component of the U.S. energy portfolio. Before growing such crops across wide areas, it is important to understand both the risks and benefits of such an action. Because of similarities between many bioenergy crops and plant invaders, and the onset of new projects to scale-up biomass production rapidly in the Midwest, it is important to understand the potential behavior of candidate species for bioenergy production outside of cultivation. We quantified the age-specific demographic rates of the Illinois clone variety of Miscanthus × giganteus, a leading bioenergy crop in the Midwest. All M. × giganteus demographic rates were strongly dependent on plant age. Spikelet production was low in first-year plants and rose to more than 180,000 spikelets per plant by the fourth year, but none yielded seedlings. Vegetative expansion of M. × giganteus was moderate compared with other large grasses; 4-yr-old plants were observed to have an average vegetative creep radius of 0.15 m yr−1. Survival of first-year plants was low, 24%, but quickly rose to 97% by the fourth year. The lack of viable seed production and slow vegetative expansion in M. × giganteus observed in this study suggest that the sterile clonal cultivar for this bioenergy crop has low invasive potential in Illinois, assuming that the tough rhizomes are not fragmented by disturbance. However, several similarities between M. × giganteus and other large-statured invasive grasses suggest that caution must be taken when introducing this species, and the potential for rhizome establishment and dispersal must be explored in greater detail.