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Does a Natural Flood Regime Effectively Control Tamarisk?

By Greg Larson


Tamarisk (tamarix romosissima) is an invasive riparian shrub that can replace native riparian vegetation, reduce physical and biological habitat complexity, and transpire large amounts of water. Thus, tamarisk is a major concern of western land and river managers. Managed reservoir releases have been suggested as a control method in some regulated river systems where encroachment by tamarisk has been concomitant with channel narrowing. We investigated the distribution of tamarisk under a natural flood regime and a dam-regulated regime on the comparably-sized Yampa and upper Green Rivers in Dinosaur National Monument. On both rivers, tamarisk germinates between the stage of base flow and the flood of record. On the regulated upper Green River, this is a narrow elevation range, but the range is much larger on the unregulated Yampa River. Approximately 60% of all tamarisk-covered area is on deposits that are inundated less frequently than every two years. Although most low-elevation deposits within the active channel of both rivers are scoured too frequently to be colonized by tamarisk, 40% of all tamarisk areas are inundated more frequently than once in 2 years. Large magnitude, infrequent floods scour tamarisk at low elevation but distribute seeds and water at high elevation, where dense groves of shrubs subsequently develop. Over one third of the tamarisk on the Yampa are established on deposits that were only inundated by the flood of record. On the upper Green River, more than 70% of all tamarisk are on deposits which formed since flow regulation began in 1962 and have only been inundated 5 times since then. Of 37 tamarisk plants that were excavated and aged in Yampa Canyon, 84% germinated in years with peak discharges greater than the 2-year flood. Of these samples, 87% germinated in years that were followed by floods of between 46% and 53% smaller. Only 5 tamarisk sampled on the Yampa River germinated prior to the 1984 flood of record, indicating that many older shrubs were scoured. Pre-1984 individuals all germinated at least 2 m above base flow stage, and there are no old individuals at lower elevations

Topics: Life Sciences, Physical Sciences and Mathematics, Social and Behavioral Sciences
Publisher: DigitalCommons@USU
Year: 2004
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Provided by: DigitalCommons@USU
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