PORTER, Marianne/E; KEARSLEY, Mike: Near-shore vegetation responses to experimental flows in Grand Canyon

We examine the responses of four clonal herbaceous species and a dominating exotic to a three-month experimental low steady flow on the Colorado River through Grand Canyon. Plant density, soil moisture, soil texture, and soil temperature data were collected on transects from the low steady flow water’s edge at approximately 8,000 cfs to the top of power plant capacity, approximately 33,000 cfs. Equisetum species colonization of newly exposed beach area increased throughout the duration of this experiment. Similar patterns are seen in three other herbaceous riparian species (Pragmitis australis, Carex aquatlilus, and Juncus species). Early in the experimental flows we see significant mortality of extant Equisetum [P=0.0001]. In addition to increasing herbaceous riparian vegetation, we see significant increases in exotic Tamarisk seedling establishment [P=0.000]. After three months establishment time, we see a decrease of approximately 60% in Tamarisk seedlings following a spike flow of approximately 33,000 cfs for four days ending the low steady experimental flow. This experiment was designed to create habitat and increase the food base for native endangered fishes. By studying the responses of riparian vegetation to experimental flows managed for fishes, we show the inter-relational nature between the terrestrial and aquatic components of the system.