Many perennial bioenergy grasses have the potential to escape cultivation and invade natural areas. We quantify dispersal, a key component in invasion, for two bioenergy candidates:Miscanthus sinensis and M. × giganteus. For each species, approximately 1 × 106 caryopses dispersed anemochorously from a point source into traps placed in annuli near the source (0.5 to 5 m; 1.6 to 16.4 ft) and in arcs (10 to 400 m) in the prevailing wind direction. For both species, most caryopses (95% for M. sinensis and 77% for M. × giganteus) were captured within 50 m of the source, but a small percentage (0.2 to 3%) were captured at 300 m and 400 m. Using a maximum-likelihood approach, we evaluated the degree of support in our empirical dispersal data for competing functions to describe seed-dispersal kernels. Fat-tailed functions (lognormal, Weibull, and gamma (Γ)) fit dispersal patterns best for both species overall, but because M. sinensis dispersal distances were significantly affected by wind speed, curves were also fit separately for dispersal distances in low, moderate, and high wind events. Wind speeds shifted the M. sinensis dispersal curve from a thin-tailed exponential function at low speeds to fat-tailed lognormal functions at moderate and high wind speeds. M. sinensis caryopses traveled farther in higher wind speeds (low, 30 m; moderate, 150 m; high, 400 m). Our results demonstrate the ability of Miscanthus caryopses to travel long distances and raise important implications for potential escape and invasion of fertile Miscanthus varieties from bioenergy cultivation.
Nomenclature: Eulaliagrass, Miscanthus sinensis Anderss.; giant miscanthus, Miscanthus × giganteus Anderss
Interpretive Summary: Eulaliagrass (Miscanthus sinensis) has already escaped from ornamental plantings to form large naturalized populations hundreds of meters from original planting locations (Quinn et al. 2010). Our results suggest that these new populations could have established following long-distance seed dispersal. Because the potential for long-distance dispersal and subsequent establishment has been demonstrated, it is important to take preventive measures to avoid further propagule pressure and gene flow into naturalized populations. As has been pointed out, breeders of bioenergy and ornamental varieties can take steps to minimize the potential for escape by selecting for nonshattering seedheads, engineering glabrous seeds, and inducing sterility (Quinn et al. 2010). Our results indicate a strong effect of wind speed on dispersal distance in M. sinensis. Growers should be aware of the need to monitor for escaped plants, particularly if producing fertile varieties. Because we show that most giant miscanthus (Miscanthus × giganteus) and M. sinensis seeds were trapped near the source, exhaustive monitoring efforts should be conducted on a regular basis within 50 m of production fields. In addition, because we know that a small proportion of seeds can disperse several hundred meters from a source, growers should also coordinate efforts with local land managers to ensure early detection and control of escaped plants in nearby natural areas.
