Riparian vegetation response to the March 2008 short-duration, High-Flow Experiment— Implications of timing and frequency of flood disturbance on nonnative plant establishment along the Colorado River below Glen Canyon Dam

Abstract

Riparian plant communities exhibit various levels of diversity and richness. These communities are affected by flooding and are vulnerable to colonization by nonnative species. Since 1996, a series of three high-flow experiments (HFE), or water releases designed to mimic natural seasonal flooding, have been conducted at Glen Canyon Dam, Ariz., primarily to determine the effectiveness of using high flows to conserve sediment, a limited resource. These experiments also provide opportunities to examine the susceptibility of riparian plant communities to nonnative species invasions. The third and most recent HFE was conducted from March 5 to 9, 2008, and scientists with the U.S. Geological Survey's Grand Canyon Monitoring and Research Center examined the effects of high flows on riparian vegetation as part of the overall experiment. Total plant species richness, nonnative species richness, percent plant cover, percent organic matter, and total carbon measured from sediment samples were compared for Grand Canyon riparian vegetation zones immediately following the HFE and 6 months later. These comparisons were used to determine if susceptibility to nonnative species establishment varied among riparian vegetation zones and if the timing of the HFE affected nonnative plant establishment success. The 2008 HFE primarily buried vegetation rather than scouring it. Percent nonnative cover did not differ among riparian vegetation zones; however, in the river corridor affected by Glen Canyon Dam operations, nonnative species richness showed significant variation. For example, species richness was significantly greater immediately after and 6 months following the HFE in the hydrologic zone farthest away from the shoreline, the area that represents the oldest riparian zone within the post-dam riparian area. In areas closer to the river channel, tamarisk (Tamarix ramosissima X chinensis) seedling establishment occurred (<2 percent cover) in 2008 but not to the extent reported in either 2000, a year when experimental summer flows coincided with tamarisk seed production, or in 1986, a year following several years of sustained flooding. The results from the 2008 HFE suggest that riparian vegetation zones subject to intermittent disturbance and near the river under normal dam operations are more susceptible to nonnative species introductions following a disturbance. This study also finds that the timing of an HFE affects the types of species that can become established. For example, HFEs conducted in March are associated with reduced tamarisk seedling establishment compared to disturbances later in the season. Additionally, early season, short-duration flooding that results in vegetation burial may favor clonal species. Along the Colorado River many of

Taxonomic and Compositional Differences of Ground-Dwelling Arthropods in Riparian Habitats in Glen Canyon, Arizona, USA

“…The magnitude and duration of both the 1996 and 2008 HFEs were insufficient to remove woody riparian plants, but some wetland plants close to the shoreline were removed (Kearsley and Ayers, 1999;Stevens and others, 2001;Ralston, 2010). Sediment deposition completely or partially buried plants, including coyote willow, seepwillow (Baccharis spp.…”

“…The 1996 HFE caused a 20-percent reduction in the total areal cover of woody and herbaceous plants on sandbars but this reduction was short lived, lasting less than 12 months (Kearsley and Ayers, 1999;Stevens and others, 2001). Herbaceous plant cover on sandbars doubled within 6 months of the 2008 HFE (Ralston, 2010).…”

“…Plants that recovered quickly following the 2008 HFE were ones that are well adapted to burial, such as coyote willow (Ralston, 2010). Clonal wetland plants, such as common reed, also quickly occupied (Kearsley and Ayers, 1999;Ralston 2010).…”

“…Plants that recovered quickly following the 2008 HFE were ones that are well adapted to burial, such as coyote willow (Ralston, 2010). Clonal wetland plants, such as common reed, also quickly occupied (Kearsley and Ayers, 1999;Ralston 2010). Seed banks were immediately depleted during the 1996 HFE, which resulted in a localized reduction in sources of seeds for germination (Kearsley and Ayers, 1999).…”

Transient simulation of groundwater levels within a sandbar of the Colorado River, Marble Canyon, Arizona, 2004

“…Emergent bars create terrestrial habitats for riparian vegetation and low-velocity aquatic habitats for fish and other benthos, act as a source of fine sediment for aeolian processes that may be integral in the preservation of archeological resources, and are used by boaters and other visitors for recreation (Rubin and others, 2002;Draut and others, 2005;Kaplinski and others, 2005;Topping and others;Behn and others, 2010;Ralston, 2010). Given the current decline in sediment storage of the post-dam Colorado River in both Marble and Grand Canyons, and the importance of eddy sandbars within the downstream ecosystem, efforts have been made to understand both the long-term stability of the eddy deposits upon emergence and the efficacy of high-flow experiments to rebuild and maintain the eddy deposits (Hazel and others, 2010;Schmidt and Grams, 2011a;Alvarez and Schmeeckle, 2012).…”