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Davis, CA, United States

Beller E.E.,San Francisco Estuary Institute | Downs P.W.,University of Plymouth | Grossinger R.M.,San Francisco Estuary Institute | Orr B.K.,Stillwater science | Salomon M.N.,San Francisco Estuary Institute
Landscape Ecology

Context: Effective river restoration requires understanding a system’s potential to support desired functions. This can be challenging to discern in the modern landscape, where natural complexity and heterogeneity are often heavily suppressed or modified. Historical analysis is therefore a valuable tool to provide the long-term perspective on riverine patterns, processes, and ecosystem change needed to set appropriate environmental management goals and strategies. Objective: In this study, we reconstructed historical (early 1800s) riparian conditions, river corridor extent, and dry-season flow on the lower Santa Clara River in southern California, with the goal of using this enhanced understanding to inform restoration and management activities. Method: Hundreds of cartographic, textual, and visual accounts were integrated into a GIS database of historical river characteristics. Results: We found that the river was characterized by an extremely broad river corridor and a diverse mosaic of riparian communities that varied by reach, from extensive (>100 ha) willow-cottonwood forests to xeric scrublands. Reach-scale ecological heterogeneity was linked to local variations in dry-season water availability, which was in turn underpinned by regional geophysical controls on groundwater and surface flow. Conclusions: Although human actions have greatly impacted the river’s extent, baseflow hydrology, and riparian habitats, many ecological attributes persist in more limited form, in large part facilitated by these fundamental hydrogeological controls. By drawing on a heretofore untapped dataset of spatially explicit and long-term environmental data, these findings improve our understanding of the river’s historical and current conditions and allow the derivation of reach-differentiated restoration and management opportunities that take advantage of local potential. © 2015, Springer Science+Business Media Dordrecht. Source

Keyes C.R.,University of Montana | Teraoka E.K.,Stillwater science

Restoration of second-growth riparian stands has become an important issue for managers of redwood (Sequoia sempervirens [D. Don] Endl.) forest reserves. Identifying differences between old-growth and second-growth forest vegetation is a necessary step in evaluating restoration needs and targets. The objective of this study was to characterize and contrast vegetation structure and composition in old-growth and unmanaged second-growth riparian forests in adjacent, geomorphologically similar watersheds at Redwood National Park. In the old-growth, redwood was the dominant overstory species in terms of stem density, basal area, and importance values. Second-growth was dominated by red alder (Alnus rubra Bong.), Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco), and redwood. Understory species were similar in both forests, with several key differences: Oxalis oregana Nutt. and Trillium ovatum Pursh had greater importance values in the old-growth, and Vaccinium parvifolium Sm., Dryopteris spp. and sedges Carex spp. had greater importance values in the second-growth. Notable differences in structure and composition suggest that restoration practices such as thinning could expedite the acquisition of old-growth characteristics in second-growth riparian forests. © 2014 by the authors. Source

Venditti J.G.,Simon Fraser University | Nelson P.A.,University of California at Berkeley | Nelson P.A.,University of Genoa | Minear J.T.,University of California at Berkeley | And 4 more authors.
Journal of Geophysical Research: Earth Surface

Sediment supply is widely held to be one of the primary controls on bar topography in alluvial channels, yet quantitative linkages between sediment supply and bar topography are not well developed. We explore the conditions under which alternate bars form and how they respond to the elimination of sediment supply in two linked laboratory experiments. The first set of experiments was conducted in a 28m long, 0.86m wide flume channel using a unimodal sand-gravel mix. The second set of experiments was conducted at field scale in a 55m long, 2.74m wide channel using a unimodal gravel mixture. In both experiments, alternate bars and patchy surface grain-size distributions developed under steady flow and sediment supply conditions. The cessation of the sediment supply induced a reduction in the surface grain-size heterogeneity and the bars were eliminated. In both flumes, mean boundary shear stress had declined, but were capable of moving sediments after the bars disappeared, albeit at relatively small rates compared to when the bars were present. In the smaller flume, the previously stationary bars migrated out of the flume and were not replaced with new bars. A nearly featureless bed formed with limited surface grain-size heterogeneity, a slightly coarsened surface and a slightly reduced slope. In the larger flume, the formation of alternate bars was induced by an imposed upstream flow constriction and as such, the bars did not migrate. Termination of sediment supply led to progressive erosion of bed topography and loss of the bars, coarsening of the bed surface, loss of bed texture patchiness and significant slope reduction. The original alternate bar topography redeveloped when the sediment supply was restored once sufficient deposition had occurred to reconstruct the original channel slope. This shows that the bar loss was reversible by establishing the previous conditions and highlights the importance of sediment supply for bar formation. The role of sediment supply in bar formation and stability is not often recognized in stream restoration. Our results suggest that the loss of sediment supply can significantly affect alternate bar topography and that considerable volumes of sediment may be needed restore channel bars. © 2012. American Geophysical Union. All Rights Reserved. Source

Stella J.C.,New York University | Battles J.J.,University of California at Berkeley | McBride J.R.,University of California at Berkeley | Orr B.K.,Stillwater science
Restoration Ecology

Seasonal water limitation exerts a strong ecological filter on stream communities in semiarid regions. For first-year riparian willow and poplar tree seedlings, desiccation from rapidly declining river flows can limit reproduction, especially on rivers in which flow regulation and land conversion have limited the amount of area available for recruitment. We investigated survivorship of first-year riparian seedlings to simulated river stage declines, focusing on the three dominant species in California's heavily regulated San Joaquin Basin: Fremont cottonwood, Goodding's black willow, and sandbar willow. Seedlings grown in mesocosms were subjected to water table decline rates typical in spring on unregulated and regulated rivers. We compared species' differences in survival time and fit the empirical data to accelerated failure time models that predicted time until death as a function of drawdown rate, initial seedling size, and maternal line. We used Akaike information criteria to select the best model for each species. Water table decline rates ≥ 6 cm/day were lethal to all species. At an intermediate rate (3 cm/day) survival varied most among species (12-38%) and was highest for Goodding's black willow. Failure time models indicated no maternal effects on survival but that initial seedling size was important for cottonwood. Using these models, we simulated survivable flow scenarios on the Tuolumne River (CA) and assessed the survivability of actual flow releases in two representative years. This modeling approach shows promise for optimizing flow releases to restore pioneer riparian habitat on regulated rivers in some of the world's most water-limited regions. © 2010 Society for Ecological Restoration International. Source

Downs P.W.,University of Plymouth | Singer M.S.,Stillwater science | Orr B.K.,Stillwater science | Diggory Z.E.,Stillwater science | Church T.C.,University of California at Berkeley
Environmental Management

The goal of restoring ecological integrity in rivers is frequently accompanied by an assumption that a comparative reference reach can be identified to represent minimally impaired conditions. However, in many regulated rivers, no credible historical, morphological or process-based reference reach exists. Resilient restoration designs should instead be framed around naturalization, using multiple analytical references derived from empirically-calibrated field- and model-based techniques to develop an integrated ecological reference condition. This requires baseline data which are rarely collected despite increasing evidence for systematic deficiencies in restoration practice. We illustrate the utility of baseline data collection in restoration planning for the highly fragmented and regulated lower Merced River, California, USA. The restoration design was developed using various baseline data surveys, monitoring, and modeling within an adaptive management framework. Baseline data assisted in transforming conceptual models of ecosystem function into specific restoration challenges, defining analytical references of the expected relationships among ecological parameters required for restoration, and specifying performance criteria for post-project monitoring and evaluation. In this way the study is an example of process-based morphological restoration designed to prompt recovery of ecosystem processes and resilience. For the Merced River, we illustrate that project-specific baseline data collection is a necessary precursor in developing performance-based restoration designs and addressing scale-related uncertainties, such as whether periodic gravel augmentation will sustain bed recovery and whether piecemeal efforts will improve ecological integrity. Given the numerous impediments to full, historical, restoration in many river systems, it seems apparent that projects of naturalization are a critical step in reducing the deleterious impacts of fragmented rivers worldwide. © 2011 Springer Science+Business Media, LLC. Source

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