The National Park Service is planning to start the restoration of the Elwha River ecosystem in Olympic National Park by removing two high head dams beginning in 2011. The potential for dispersal of exotic plants into dewatered reservoirs following dam removal, which would inhibit restoration of native vegetation, is of great concern. We focused on predicting long-distance dispersal of invasive exotic plants rather than diffusive spread because local sources of invasive species have been surveyed. We included the long-distance dispersal vectors: wind, water, birds, beavers, ungulates, and users of roads and trails. Using information about the current distribution of invasive species from two surveys, various geographic information system techniques and models, and statistical methods, we identified high-priority areas for Park staff to treat prior to dam removal, and areas of the dewatered reservoirs at risk after dam removal.
Rivers are vital ecosystems that support aquatic and terrestrial biodiversity and several ecosystem services, including food, water, culture, and recreation. After centuries of building dams on rivers across the world, dam removal projects are now on the rise due to obsolescence, reservoir sedimentation, insufficient return on investment, or river restoration and conservation priorities. Most dam removal projects have focused on smaller structures (< 10 m in structural height), but larger structures have also started to be removed in increasing numbers as practitioners, river managers, conservationists, and the public have gained more experience with the practice. Recent estimates suggest that only a small fraction of dam removals have been scientifically studied, and include mostly small dams and short time scales. Documenting the long-term ecological outcomes of large dam removal (i.e. >10 m tall) represents a new frontier in dam removal research: projects are more recent and provide an opportunity to understand the complex ecological changes that occur with these transformative restoration projects. Here, we aim to collate a diverse array of papers on long-term dam removal research projects involving larger dams (>10 m) to synthesize the issues, outcomes, tools, and experimental designs used to study large dam removal projects from physical, biological, and ecological perspectives. With this collection, we aim to showcase diverse global projects on ecosystem responses to large dam removal; collect perspectives from different disciplines, fields, and geographies; and synthesize the current state of knowledge in this area. We expect that this Research Topic will be informative to ongoing, long-term ecological restoration and monitoring projects related to dam removal as well as to upcoming large dam removal projects. We welcome contributions from all disciplines addressing the physical, ecological, and ecosystem responses to large-scale dam removal. Contributions could include original research in a specific discipline or area, case studies, or synthesis papers that address one or more of these topics in a transdisciplinary approach. Contributors could address any of the following major topics as related to outcomes of large dam removal, alone or in combination: Freshwater, estuarine, and marine aquatic biota; River and reservoir geomorphology; Terrestrial and riparian vegetation; Wildlife; Sedimentation; and Modelling. We would like contributors to highlight key results in their area of study, cross-disciplinary insights, and lessons learned that could inform ongoing monitoring and research efforts in current projects as well as upcoming large dam removals.
"Riparian ecosystems are important for ecological functioning of rivers, and are significantly impacted by dams. With over 50% of large dams in the U.S. beyond their life expectancy, dam removal is increasingly being considered to eliminate aging infrastructure and restore ecosystems. There have been few large dam removals to date, so studies assessing vegetation succession on exposed reservoir sediments are limited. My research aims to assess how environmental factors within exposed reservoirs affect vegetation succession following removal of two dams on the Elwha River, Washington. In addition, I compared patterns of vegetation among the two reservoirs and their landforms. To do this, I sampled 67 100m2 plots in 2013 and 60 100m2 plots in 2014 along 10 transects within Mills and Aldwell Reservoirs. In each plot , I recorded vascular plant species composition and woody species height. I collected and pooled 8 soil samples (20 cm) / plot to assess percent organic matter, nutrients, and percent sand, silt, clay, and conducted a Wolman Pebble Count. I used a structural equation models to show how environmental factors related to hydrology, soil nutrients, and dispersal distance affect species diversity and cover. I compared environmental factors and vegetation responses among the two reservoirs using general linear models. Structural equation models showed that soil nutrient levels, sediment texture, ground cover, and landform were the environmental factors most related to reservoir revegetation patterns. Native species richness and cover, and exotic species cover were highest on valley walls and were positively related to high percent organic matter and % silt, but negatively related to % litter, D50, Mg, and P. In contrast, exotic richness was highest on terrace and riparian landforms with low % litter, Mg, and P and high % organic matter that were furthest away from established forest communities. Sediment nutrient indicator variables organic matter, Mg, and P were co-correlated with other sediment variables and act only as a surrogate for those variables in these models. In total, 147 vascular plant species were sampled in the two reservoirs of which 47 (31%) were exotic. Aldwell reservoir contained higher native and exotic species richness, cover, and woody species growth, and had finer textured sediments, deeper sediment depth to refusal, and higher % litter ground cover than Mills reservoir in 2013, while Mills reservoir had higher % gravel ground cover. By 2014, the only significant difference between reservoirs was woody species height, which was higher in Aldwell reservoir. Native species richness and cover were higher than that of exotic species in both reservoirs; however, exotic species are increasing, particularly along riparian zones within both reservoirs and on the most fertile sites along Aldwell valley walls and terraces. The increase in exotic species occurred despite active management to control them, and should be a concern to Olympic National Park because the reservoirs could become a gateway of exotic species invasion into a relatively protected landscape. Over time, I expect multiple vegetation communities to form within each reservoir associated with landform. Valley walls will likely return to the composition and structure of surrounding upland forests, while riparian zones will likely come to resemble the upstream Elwha River reaches not affected by damming. Terraces, on the other hand, will likely form novel vegetation communities dependent on environmental factors that will differ between the two reservoirs. The results of my study highlight the effect of varying environmental conditions on vegetation recovery rates and can help inform the Elwha River restoration project as well as any future dam removal projects"--Leaves iv-v.
Invasive exotic plants pose a serious threat to the natural resources of many national parks. Invasive species can displace native plant species, inhibit the regeneration of native forest trees, degrade habitats for rare species, and alter vegetation community structure and composition. Due to these potentially serious impacts; the status, trends, and early detection of invasive species is currently considered a Tier 1 vital sign for terrestrial ecosystems in the Eastern Rivers and Mountains Inventory and Monitoring Network.
Exotic plant invasion is a major environmental and ecological concern and is a particular issue for wetland ecosystems. I present statistical models that predict the locations of three exotic invasive plants (Arundo donax, Eucalyptus species (Eucalyptus globulus, Eucalyptus calmodulensis), and Tamarix ramosissima) that invade wetland areas throughout San Diego County based on their spectral signatures. I used three images that differed in their spectral resolutions and spectral coverage: Color-infrared (1m pixel size, infrared, blue and green bands), high resolution true color imagery (lm pixel size, red, blue and green bands), and hyperspectral Landsat imagery (30m pixel size, blue, green, red, near infrared, (2), mid infrared, and thermal infrared bands). For each invasive plant, three well-known multivariate statistical analyses, Discriminant Function Analysis (D.F.A.), Quadratic Discriminant Function Analysis (Q.D.F.A.), and CART, were used to identifY the models that best separated invasive plants from surrounding vegetation. A predictive accuracy analysis was preformed for each model by predicting which points should contain the invasive species based on their spectral values, then comparing these predictions to the actual presence or absence of the species. The best model for both Arundo and Eucalyptus species was obtained from the Q.D.F.A. using spectral values calculated from a combination ofNAIP and Landsat wavebands. CART using spectral values obtained from Landsat imagery produced the best results for Tamarix. Past studies show that plant species do in fact have distinct spectral signatures however; further investigation of classification techniques for this study is needed in order to create a more successful predictive model for each invasive plant species. Key-words: Discriminant Function Analysis, CART Model, hyperspectral imagery, invasive plants, predictive model, spectral signatures.
