The North American beaver (Castor canadensis) engineers ecosystems through both the creation of dams that favor flood-tolerant vegetation and the abandonment of dams that attract fast-growing and fast-dispersing species. This change in vegetative composition, while noted in other ecosystems, has yet to be studied in the NC Piedmont region of the United States. We investigated how the species composition of floodplain plant communities responds to dam construction and modification by measuring beta and gamma diversity and invasive species abundance. We utilized four sites for each of our two treatment levels and reference: current damming (DAM), abandoned or past damming (ABN), and reference or unmodified sites (REF). We found higher beta diversity based on a significant difference in species composition among the three treatments (p<0.001), likely due to a higher flood tolerance in DAM sites compared to REF sites (p=0.0012). Our estimation of gamma diversity only showed a slight increase from 49.2 ± 2.2 to 51.6 ± 4.4, possibly due to the already high plant diversity in the Piedmont. Additionally, the 60% invasive species abundance in ABN treatment was significantly higher than DAM and REF. Restoration efforts must be made not only to protect dams and therefore plant diversity, but also preserve dams to prevent the spread of invasive species.
