1. Potential Invasive Plant Establishment After Dam Removal: A Case Study of the Elwha River Dams Trevor Sheffels November 25, 2009

2. Outline Background –Dam removal in the United States –Invasive plant establishment Research on invasions after dam removal Case Study –History of the Elwha River –Potential invasive plant establishment

3. Outline BackgroundBackground –Dam removal in the United States –Invasive plant establishment Research on invasions after dam removal Case Study –History of the Elwha River –Potential invasive plant establishment

4. Dam Removal in the United States Majority of dams are nearing end of licensing agreements Approximately 500 dams have been removed in the last decade Pacific Northwest is prominent in dam removal discussions due to salmon migration issues

5. Importance to Limnology Conversion from manmade lentic reservoirs to natural lotic rivers Dam removal completely alters watershed biogeochemical processes Large-scale disturbance that results in variety of ecosystem impacts

6. Invasive Plant Establishment Invasive species are often found in disturbed habitats (Elton 1958) Invasive plants are often pioneer species Life history strategies allow invasive plants to outcompete native species

7. Outline Background –Dam removal in the United States –Invasive plant establishment Research on invasions after dam removalResearch on invasions after dam removal Case Study –History of the Elwha River –Potential invasive plant establishment

8. Invasions After Dam Removal Resident seed bank can contain viable invasive species seeds (Nishihiro and Washitani 2007) Natural revegetation of exposed reservoir can be prone to invasive species (Auble et al. 2007) Natural hydrology results in new source of invasive species introduction downstream (Gurnell et al. 2006) Exposed seed bank DAM REMOVAL Downstream transport Lake bed colonization

10. Outline Background –Dam removal in the United States –Invasive plant establishment Research on invasions after dam removal Case StudyCase Study –History of the Elwha River –Potential invasive plant establishment

11. Elwha River Dams Watershed covers 20% of Olympic National Park Two hydroelectric dams constructed in early 1900s Native salmon habitat has been severely restricted

12. Glines Canyon and Elwha Dams Glines Canyon Dam –210 feet tall –Lake Mills reservoir covers 415 acres Elwha Dam –108 feet tall –Lake Aldwell reservoir covers 267 acres

13. Reservoir Bed Seed Banks Seed bank is trapped mostly in fine sediment 50% of Lake Mills seed bank is viable (Brown and Chenoweth 2008) 15% of these seeds are invasive species (Brown and Chenoweth 2008)

14. Exposed Sediment 18 million cubic yards of accumulated sediment in two reservoirs (Mussman et al. 2008) 13 invasive species are present and likely to establish (Brown unpublished) Initial establishment could result in long-term problems (Orr and Stanley 2006)

15. Invasive Species Downstream Large quantity of sediment will move downstream over short period of time (Mussman et al. 2008) Natural levels of hydrochory will be restored (Brown and Chenoweth 2008) Establishment of natural stream banks may be an issue

16. Conclusions Invasive species establishment should be considered when considering tradeoffs of dam removal Processes are not well-understood and further research is needed Elwha project provides a unique opportunity to study invasive species establishment following a large dam removal

17. References Auble, G.T., P.B. Shafroth, M. Scott, and J.E. Roelle. 2007. Early vegetation development on an exposed reservoir: implications for dam removal. Journal of Environmental Management 39: 806-818. Brown, R.L. and J. Chenoweth. 2008. The effect of Glines Canyon Dam on hydrochorous seed dispersal in the Elwha River. Northwest Science 82: 197-209. Elton, Charles. 1958. The ecology of invasions by animals and plants. Methuen, London, England. Gurnell, A.M., A.J. Boitsidis, K. Thompson, and N.J. Clifford. 2006. Seed bank, seed dispersal and vegetation cover: colonization along a newly-created river channel. Journal of Vegetation Science 17: 665–674. Mussman, E.K., D. Zabowski, and S.A. Acker. 2008. Predicting secondary reservoir sediment erosion and stabilization following dam removal. Northwest Science 82: 236-246. Nishihiro J. and I. Washitani. 2007. Restoration of lakeshore vegetation using sediment seed banks: studies and practices in Lake Kasumigaura, Japan. Global Environmental Research 11: 171-177. Orr, C.H. and E.H. Stanley. 2006. Vegetation development and restoration potential of drained reservoirs following dam removal in Wisconsin. River Research and Applications 22:281-295.