Where does fertile Miscanthus × giganteus fall on the invasive spectrum: Performance, establishment, and spread

Background/Question/Methods

The 2007 Energy Independence and Security Act mandates tremendous production of transportation fuel from renewable sources by 2022, with 44% derived from cellulose. Feedstocks, many being non-native, have been selected specifically to produce large amounts of aboveground biomass, tolerate poor growing conditions while requiring minimal inputs. These ideal characters, for bioenergy production, have attracted concern for their potential to become invasive. Miscanthus × giganteus has emerged as one of the most promising bioenergy crops, but is economically limited due to sterility. Newly developed fertile varieties of M. × giganteus may streamline cultivation while reducing labor and establishment costs. Weed risk assessments suggest that this species poses ‘low risk’ for invasive potential. However, the addition of fertile seed must be evaluated for invasiveness.  

Results/Conclusions

In our effort to evaluate the invasive potential of seeded M. × giganteus in the Southeast, we compare it against ten grass species, comprising 22 cultivars, in four environments, in a head-to-head comparison of species introduced for agronomic purposes that are known invasives in the US (positive controls), and species that are known not to be invasive (negative controls). This design allows us to make relative comparisons of our candidate crops along the invasive continuum. Establishment year data indicate that under ideal agronomic conditions (weed-free) M. × giganteus densities were 215% lower than the negative controls and 96% lower than the positive weedy species. However, M. × giganteus produced 391% and 138% more culms than non-weedy and weedy controls, respectively, while the basal diameter was 288% and 102% greater than the negative and positive controls respectively. Established densities of the fertile and sterile M. × giganteus cultivars did not differ, but the seeded M. × giganteus was 57% taller and produced 23% more culms than the sterile M. × giganteus ‘Illinois’. Our data suggests that M. × giganteus may have superior biomass production, even at lower densities, compared to other grass species. However, stand establishment and growth rates were far lower than johnsongrass (a known invasive species) but much greater than big bluestem (a negative control), suggesting that seeded M. × giganteus does not present exceptional establishment year spread potential under our conditions. This establishment year data, is one component of a more comprehensive, long-term study to evaluate the invasive potential of M. × giganteus. Knowledge gained using these data help to prepare for widespread commercialization of these crops, while planning ahead for improved stewardship.