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Date Permissions Signed
Date of Award
Master of Science (MS)
Helfield, James M.
Homann, Peter S., 1953-
Hooper, David U., 1961-
The removal of Glines Canyon and Elwha dams from the Elwha River in Olympic National Park, Washington State is scheduled to begin in 2011. This undertaking is among the largest planned dam removals and ecosystem restoration projects in the world. One of the challenges associated with this restoration will be to understand processes influencing revegetation and invasive species colonization on the sediments exposed by dam removal. To help characterize post-dam vegetation succession within the Elwha River floodplain and dewatered reservoirs, we undertook field collections of reservoir sediments and seed rain during summer 2008. We then conducted two greenhouse experiments 1) to identify seed rain germinants upon fine reservoir sediments and 2) to explore effects of reservoir sediment texture on germination and growth of restoration candidate native species and potentially problematic invasive species. Measured summer seed rain was relatively low (/m2) at three sites in the Elwha Valley. This suggests that, in the initial years following dam removal, colonization by seed rain may be slow, although the observed low seed rain density may have been a function of sampling method and timing. In the second seed sowing experiment, nearly all tested species (Artemisia suksdorfii, Rubus parviflorus, Rubus spectabilis and Rubus discolor) exhibited reduced capacity for germination and growth upon post-dam reservoir surfaces, while the invasive species Cirsium arvense was unaffected when compared to present-day river substrate. These results indicate a potential colonization advantage for Cirsium arvense on reservoir sediments in the years following dam removal. Depending on additional factors such as source population sizes, seed production, seed dispersal rates, and competition during establishment, this could allow for a relative increase in Cirsium arvense populations on the new post-dam substrates. These findings have implications for revegetation efforts directed at maintaining biodiversity and ecosystem functioning on floodplain and exposed reservoir surfaces following dam removal.
Western Washington University
Elwha River (Wash.)
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Michel, James T., "Seed rain and selected species germination and growth trials: implications for natural and augmented revegetation of post-dam Elwha River floodplain and reservoir sediments" (2010). WWU Graduate School Collection. 60.