| Scope and Method of Study: Grasslands and savannas, which cover as much as 30-50% of the earth's ice-free land area, are affected by global environmental changes including biological invasions. To test the role of bud banks, an important feature of native prairie communities, in regulating invasion by exotic plants under three levels of simulated grazing (no clipping, 28 day clipping interval, and 14 day clipping interval) I conducted a greenhouse microcosm study. Using native rhizomes planted into native prairie soil, I established bud bank densities of 0, 30, 60, and 100% of mean tallgrass prairie bud bank density. Seeds of three exotic species were sown into each microcosm. The number of emerging and established exotic plants in each microcosm was counted every 14 days. I measured the aboveground biomass of each species at the end of the growing season (22 weeks). Assessments of exotic plant emergence, establishment, survivorship, reproduction, and biomass based on these measurements were compared using analysis of variance.;Findings and Conclusions: The effects of the bud bank on exotic plant emergence, establishment, and survivorship were inconsistent and relatively weak. However, reproduction and biomass of exotic species were strongly influenced by bud bank density. In the absence of clipping, the biomass of exotic species was 675% higher at the lowest bud bank density than at the highest density. Furthermore, I found evidence for an invasibility threshold between 0-30% of mean field bud bank density in tallgrass prairie. These findings improve our understanding of plant invasion and suggest that restoring and maintaining bud banks should be a priority for land managers seeking to prevent and limit plant invasions. |
