Habitat invasibility, a major determinant of invasion success by non-native plant species, depends in part upon the ability of resident species to exclude or achieve competitive dominance over exotic species. In grasslands and savannas, bud banks (belowground meristems) may be the primary source of plant recruitment, and may confer invasion resistance by enabling resident plants to preempt resources needed by potential invasive plants following disturbance or resource enrichment. To evaluate the role of bud density in regulating exotic plant invasions, we established a greenhouse microcosm study using native tallgrass prairie soil and native warm-season grass meristems. We measured the emergence, establishment, survivorship, reproduction, and aboveground biomass of three exotic, invasive species sown at equal rates into microcosms with uniformly spaced native bud densities of 0, 800, 1600, and 2680 buds/m² (0, 30, 60, and 100% of field density in tallgrass prairie ecosystems, respectively). Because herbivory is an integral component of the ecology and management of grasslands, we also included three levels of simulated herbivore grazing (no clipping, moderate, and high).
Results/Conclusions
Exotic emergence, establishment, and survivorship did not exhibit any consistent relationship with either bud density or clipping intensity. Clipping, at either moderate or high intensity, significantly reduced the number of exotic plants reaching reproductive status, compared to non-clipped plants. In contrast, the proportion of exotic plants reaching the reproductive stage was not influenced by bud density, but the aboveground biomass of plants reaching reproductive status was negatively related to bud density. At the end of the 22 week study, in our non-clipped treatments, the aboveground biomass of exotic plants was significantly greater in microcosms that did not contain native bud banks, and we observed a significant negative relationship with bud density. However, the aboveground biomass was similar between moderate and high intensity clipping treatments across all levels of bud density. Exotic aboveground biomass of the non-clipped treatment was significantly higher than moderate and high clipping treatments. We conclude that bud density regulates invasion by exotic plant species in the absence of continuous defoliation by controlling individual plant biomass and reproductive potential of exotics.