Background/Question/Methods   Biofuel crops are being selected to require minimal inputs, tolerate marginal growing conditions, and exhibit rapid growth rates—agronomically desirable traits that also characterize many of our worst invasive species. Many of the candidate biofuel crops are known invasive or noxious species in portions of their non-native range. Switchgrass (Panicum virgatum) and miscanthus (Miscanthus x giganteus) are leading biofuel candidates, and are non-native to California. Niche modeling has demonstrated that riparian areas are the ecosystems most susceptible to a potential invasion in California due to having an available water supply all year. Therefore, we conducted a controlled introduction of switchgrass and miscanthus in a riparian area to evaluate survival, establishment, and competitive ability. Seedlings of switchgrass and miscanthus were transplanted along a soil moisture gradient in a local stream channel (hereafter lowland), and in an adjacent upland site both with and without resident vegetation as a competition treatment. Survival, establishment, and performance were measured for two years. A second experiment was conducted to evaluate the establishment potential of seeds and rhizomes (as opposed to the transplants used in the first experiment).

Results/Conclusions   Nearly all miscanthus plants died in the upland plots (with and without competition), while between 30 and 45% survived in the lowland site. However, switchgrass had 40 to 70% survival in the upland and lowland sites, with more surviving under a competition-free environment. Tiller production and plant height were greatest in the lowland environment with no competition. In the lowland site, switchgrass survival was unaffected by the soil moisture gradient in the competition-free environment. However, despite the preference for wetter sites, switchgrass was only able to survive in the mid to dry sites in the competitive environment due to the presence of the highly competitive native perennial grass Leersia oryzoides. The propagule introduction study is ongoing, but is showing that neither species will germinate/emerge under water, which much of the lowland is during the winter months. However, in the upland site both species are beginning to emerge in late winter after the night temperatures are above 50 C. In conclusion, both species demonstrate an ability to establish with or without competition, especially under conditions where soil moisture is not limiting. Upland environments are too harsh for miscanthus, and only support weakly performing switchgrass.