Agronomy Department, University of Florida, Gainesville, FL 32611, USA
Introduction of species to non-native ranges worldwide shows no sign of decline and many ecosystems are now subject to multiple plant invaders. Meanwhile, funding for management of conservation areas often is inadequate to address even a subset of the problematic invasive species. A better understanding of the long-term dynamics and impacts of plant invasions is needed to distinguish between species that will persist and affect native ecosystems and those that may naturally decline over time. However, most research projects on invasive plant impacts are conducted for only a few years, greatly limiting our ability to measure longer-term changes in populations or their effects. Using examples from studies of Microstegium vimineum in Indiana and Imperata cylindrica in Florida, I explore the biotic and abiotic drivers underlying the persistence or decline of invaders. For example, Microstegium can have profound impacts on native species in eastern deciduous forests, but the results from an eight-year experimental invasion study show that the invader and its effects can decline over successional time and allow native species to return. In other cases, however, Microstegium, Imperata, and other invaders persist over the long-term and negatively impact native species and alter ecosystem processes. In addition, fire, the accumulation of pathogens, interactions among multiple invaders, and other factors may determine if, and under what conditions, species may persist or decline. Improving our understanding of how invasions and their effects change over time will require additional monitoring and experiments over multiple years and will help prioritize the efficient and effective use of limited management funds.