Germination and establishment of bioenergy grasses outside cultivation: a multi-region seed addition experiment

Many invasive plants originate as cultivated species. The growing demand for renewable energy has stimulated agricultural production of native and non-native perennial grasses, but little is known about their potential to become invasive outside cultivation, particularly at the early establishment phase. We evaluated effects of propagule pressure and establishment limitations for early establishment of four potential bioenergy grasses in agricultural field margins and forest understory across a 6.3° latitudinal gradient (Ontario, Canada; Illinois and Virginia, USA). We used multiple seed introductions in different years and followed their fate for up to three growing seasons. High interannual variability in establishment indicates that the frequency of propagule introduction is important for invasion outside cultivation. Establishment limitations were stronger in forest than field margins; of 328,800 seeds added, only 1 of 505 persisting seedlings occurred in forest. Removal of competing vegetation had small and variable effects on establishment among sites and species. Unlike previous short-term experiments, our results indicate the potential for the persistence of these bioenergy grasses in both vegetation and seed bank, and highlight the importance of long-term experiments in evaluating invasion risk.