| dc.description.abstract | Tallgrass prairie was once widespread in North America prior to European settlement, but now is almost entirely gone from the landscape. As a result, there has been a diligent effort to restore portions of land back to tallgrass prairie. However, these restorations often fall short of restoring the plant diversity and plant community composition seen in undisturbed prairies. In this dissertation, I use ideas in ecological theory to overcome two practical challenges practitioners face that diminish plant diversity in prairie restorations. One potential reason that restored prairies often have lower diversity than undisturbed prairies is that undisturbed prairies exhibit an aggregated spatial structure that may enhance coexistence, while tallgrass prairie restorations have a uniform spatial structure that may encourage competitive exclusion. In chapter 1, I explore how the initial spatial structure of sown species affects the diversity and composition of the sown plant community, as well as the establishment of weeds in tallgrass prairie restorations. In this experiment, we manipulated the level of aggregation in experimental restorations and the functional similarity of aggregates. We found that the initial spatial arrangement of sown species substantially affects the outcome of restorations by altering the establishment of sown and non-sown species. Invasive species are economically problematic and are suspected to be a leading cause of species extinction. Sericea, an invasive legume, is a particularly important invasive species in the Midwestern U.S. because of its potential to reduce to quality of grasslands. In chapter 2, I examine a large-scale data set from Fort Riley Military Reserve (FRMR) to determine if tallgrass prairie is intrinsically more resistant to Sericea invasion than disturbed grasslands, and to what degree human activity and propagule pressure affect the spread of Sericea across the landscape. Results showed that tallgrass prairie is more resistant to Sericea than disturbed grasslands. We also found that human activities likely aid in Sericea’s invasion by disturbing the plant community and facilitating seed dispersal. Our findings enhance understanding of invasion ecology and the factors driving Sericea invasion. In chapter 3, we sought to further refine our understanding of which characteristics of tallgrass prairies confer invasion resistance: the abundance of dominant, competitive species or their relatively high plant diversity. We also sought to explore the efficacy of adding tallgrass prairie restoration to existing Sericea management methods in controlling Sericea abundance on previously invaded land. In our restorations, we varied the methods used for site preparation, the density and diversity of seed mixes used, and the use of follow-up herbicide. We found that the site preparation used for restoration, the density of the seed mix, and the use of follow-up herbicide all affect the re-invasion of Sericea, but the diversity of the seed mix does not. Our results support the idea that dominant species are primarily responsible for conferring invasion resistance and demonstrate that incorporating tallgrass prairie restoration may be beneficial for Sericea management. Overall, the results in the dissertation show that incorporating ecological theory into restoration practice is worthwhile. It not only advances our understanding of what regulates ecosystems, but can also improve the methods used in restoration practice, and ultimately improve our ability to restore degraded ecosystems. | |
