Evaluating the influence of wind speed on caryopsis dispersal of Miscanthus sinensis and Miscanthus x. giganteus

Authors: QUINN, L - University Of Illinois; Matlaga, David; STEWART, R - University Of Illinois; Davis, Adam

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2010
Publication Date: 1/1/2011
Citation: Quinn, L.D., Matlaga, D.P., Stewart, R., Davis, A.S. 2011. Evaluating the influence of wind speed on caryopsis dispersal of Miscanthus sinensis and Miscanthus x. giganteus. Journal of Invasive Plant Science and Management. 4(1):142-150.

Interpretive Summary: The search for renewable energy sources has focused intense interest on perennial grasses capable of producing huge amounts of biomass for co-firing or conversion to ethanol. There is concern that some candidate species may be able to escape cultivation and form invasive populations in parks and along roadsides. Therefore, it is important that dispersal ability be considered prior to large-scale planting of such species. In the Midwest U.S., two perennial grasses in the genus Miscanthus, Chinese Silver grass (M. sinensis) and Giant miscanthus (M. x giganteus) are being considered as biofuel crops. Chinese silver grass, which makes fertile wind-borne seeds, has a long history of ornamental use in the U.S. and is known to escape and form self-sustaining populations outside of cultivation. Giant miscanthus is thought to produce only sterile seeds due to its genetic makeup. As part of our efforts to assess the invasive potential of Miscanthus bioenergy feedstocks, we measured seed dispersal distances for both Chinese silver grass and Giant miscanthus within post-harvest agricultural fields in Urbana, IL. For both grasses the majority of seeds (95% for Chinese silver grass and 77% for Giant miscanthus) were captured within 50 m of the source, but a small percentage (less than 3%) were captured at 300 m and 400 m. Most of the long distance seed dispersal was associated with periods of greater wind speed (greater than 10 m/sec). Our results help explain the rapid spread of naturalized Chinese silver grass populations in the eastern U.S. Looking forward, these results will be used as components of quantitative models of invasion risk for Miscanthus bioenergy feedstock crops.

Technical Abstract: With the increasing demand for alternative energy sources, perennial grasses are being evaluated for biomass production on large scales. Yet there is concern that some candidate species have the potential to escape cultivation and invade natural areas. Therefore, it is important that components of the invasion process (e.g. dispersal ability and demographic performance) be assessed prior to full scale deployment. In the Midwest U.S. two species in the genus Miscanthus, M. sinensis and M. x giganteus are being considered as potential biofeedstocks. Miscanthus sinensis produces fertile, wind dispersed seeds and has a long history of ornamental use in the U.S. and is known to escape cultivation and form naturalized populations. Miscanthus x giganteus is a triploid hybrid and is thought to only produce sterile caryopses. To estimate the distance caryopses of both Miscanthus species can disperse and to quantify the shape of the dispersal kernel we performed a field experiment in Urbana, IL. For each species, a point source of over one million caryopses was placed in a harvested agricultural field and allowed to disperse anemochorously for approximately 6 weeks. A single trial was run for each species, separated in time to avoid confusing caryopses. Sticky traps were placed in annuli near the seed source (0.5 to 5 m) and in arcs (10 to 400 m) radiating out from the seed source in the prevailing wind direction and were censused biweekly for captured seeds. Daily wind speeds were recorded during the trials and average speeds were calculated biweekly. During the trials the number of caryopses captured differed considerably between species, 75 for M. x giganteus and 455 for M. sinensis. For both species the majority of caryopses (95% for M. sinensis and 77% for M. x giganteus) were captured within 50 m of the source, but a small percentage (0.2% - 3%) were captured at 300 m and 400 m. The distance that M. sinensis caryopses traveled was strongly influenced by wind speed, with higher wind speeds (e.g. > 10 m/s) resulting in greater likelihood for seed capture in distant traps (e.g. 400 m). Our results help in explaining the rapid speed at which M. sinensis populations have spread in the eastern U.S. and provide a key component in understanding the spatial scale at which these candidate biofeedstocks could deposit propagules outside of production fields.