Portland State University. Department of Geography
Date of Award
Master of Science (M.S.) in Geography
1 online resource (v, 65 pages)
Dam retirement -- Washington (State) -- Skamania County -- Case studies, Revegetation -- Washington (State) -- Skamania County -- Case studies, Dam retirement -- Environmental aspects -- Washington (State) -- Skamania County -- Case studies
Dam removals are becoming increasingly common as dams reach their life expectancy and face costly upgrades associated with relicensing. Though removal is often viewed as a success in terms of ecological restoration, it also represents a major disturbance to an area. Previous research has shown that native species do not survive as well at these disturbed sites, and invasive species often dominate. This study examines the vegetation response in the drained reservoir area after the removal of Hemlock Dam on Trout Creek, a tributary to the Wind River in southern Washington. Transects were established and quadrats were sampled to determine the plant classifications and cover of vegetation and to examine possible correlations between environmental variables and the spatial distribution of plant classification groups. Sampling took place in the third and fourth years following dam removal, and the data was analyzed to determine significant changes and relationships.
The results of this study showed that the site was dominated by a volunteer native forb Lotus purshianus (Spanish clover) and a planted native tree Alnus rubra (red alder). Most of the other species found were native volunteer forbs and grasses characteristic of early succession in this region. Both invasive species and planted species, with the exception of Alnus rubra, had low canopy covers. There was a significant increase in native plant canopy cover, as well as total canopy cover, from 2012 to 2013. There were also significant relationships between plant classification groups and environmental variables, including soil infiltration, elevation, and distance from stream. This study will help inform resource managers about the kinds of plants that will volunteer after dam removals and the possible success of re-vegetation projects.
Ramsey, Greer Stewart, "An Analysis of Vegetation Recovery following Dam Removal at Hemlock Recreation Site, Washington" (2014). Dissertations and Theses. Paper 2003.